Most techs won't even take in a solid state amp. The repair cost exceeds it's value so good on you for doing it for a nominal fee. I'd pay your price for the simple fact that if I like the amp I'll pay to keep it alive.
Good video tutorial. I have fixed loads of Valvestate amps myself. Most of the issues are caused by broken solder joints on the jack sockets, oxidised contacts on the send/return loop, oxidation/dirt on the first gain control and of course that first TL072 chip which is the fault you found here. The chip is knocked-out by static from guitar leads and stray voltages from guitar pedals. It gets noisier as time goes by and eventually dies. Later Valvestate amps have better protection circuitry on the input jack. It doesn't help the way the first gain stage is wired-up on some of these amps. Instead of using a fixed resistor in the feedback loop on that opamp, Marshall have worked the variable resistor in there instead. Dirty contacts on that control sound terrible!
Excellent and informative video Stuart . I fully understand your work ethics being a retired (71) electrician. I:m more than happy to do small works for small,ish rewards. Still enjoy the buzz... Cheers and keep up the good work.
Stuart, I enjoy it when you do the live thing when troubleshooting. The talking through the process is valuable to someone with my level of knowledge. Learning how to think is a wonderful activity and is exacty why i began this journey. I truly appreciate your ability to make it understandable. Mike
I really appreciate your videos. They are both informative for specific problems, but also show an effective approach to problem-solving. I have learned a lot of practical techniques from you in a short time indicating to me at least, the effectiveness of your videos. Thanks very much!
Nice to have the thinking behind the troubleshooting process explained clearly. I have a small Marshall amp where the sound suddenly cuts out when in use and it's given me ideas of where to look for problems that are within my ability.
Fine job and I appreciate your diagnostic methods. As an auto technician now retired I was taught the same way. Positive test everything you can to make a determination.
Years ago, I had a 100w valvestate head and a 4x12 cab which served me for a 1000 gigs and never let me down. The sound was superb. Then I became a pro guitarist and thought I needed expensive gear so I bought many various amps including Mesa, soldano etc but they never could produce that sound I got from a £300 rig! I really miss that amp!
Very nice. I've bought many amps for cheap that were heading for the bin. In 95% of cases all the amps needed was a good jack cleaning (sometimes the finger switches are bent) and one or more cold solder joints. On the one hand I hate that people have such a disposable mindset that they would throw away an amp instead of fixing it, but on the other hand, if they fixed them then I wouldn't get perfectly good amps for pennies on the dollar. I just bought today this same amp, the VS580 for $35. Nothing wrong with it except a broken fuse holder.
I think they simply don't know how to fix, or know anyoine who can. The amp's been in the loft for 15 years and they just want rid. Your gain, as you say!
Lovely repair. I bought a vs100 for 100€ which the seller said it had a strange noise. The thing was oscilating because of cracked solder joints. Got that fixed. It still has a bit of a hum, mostly when its heating up the valve. Thanks for the video.
Hi Stuart, I enjoyed this fix. It might be worth keeping a small journal with model names and what the issue was. Easy to flick through when you receive more work. I'm aware yes it is already on film, just thought it might be easier to get the data you need.
Thanks Otto. As you might guess I already have a substantial spreadshet containing full details of the several thousand amps I have repaired. Suprisignly, it rarely comes into play to help diagnose a new issue. Stuart
Excellent work Stew. Many thanks for posting. Took me back forty-odd years and my training in fault-finding when an apprentice electrician. We actually trained on valve amps etc. Sadly I never stuck at it. If only I knew then what I know now.
Don't know how I missed this one. I have worked on this same breed several times, and every time so far, the same culprit. I think we may need to stock up on ic sockets, or design a conversion to a ecc/12ax7 :) Keep them coming always Stu. And always enjoy going on the ride with you. If you are interested in old rotten cars being resurrected, hope you will pop into my new series of videos. I could use as many subscribers as I can get to get off the ground.
Thanks. No, old cars aren;t my thing at all. It's quite a slow burn building up subscribers from scratch but if the content is good, you'll steadily add people. Forget about monetising the channel though - almost impossible these days.
Hi Mark. One way to rest for loose connection or dry joint is to play some music through it (e.g. from your phone) then give the amp a couple of sharp bangs on the top with your fist. If you hear loud crack when you do this, or sound comes/goes it's defo a dry joint etc. Other than that, an amp tech should be able to sort it for you.
Nice fix Stuart, like the walk thru and your clever tricks and methods to find the problems..Great learning experience for us newbies..Thanks again for sharing..Ed..uk..😀
I have the Marshall stereo valvestate vs265 and it has the chorus 3-channel stereo, clean, overdrive one, overdrive 2 & overdrive EQ as far as any name goes with this it just says valve state Vs265. Anyway I have saved this video and I'm not really an electric technician but I love electronics, I can troubleshoot a little bit but I'm going to fix my amp, its been my favorite amp, & thanks to you I'm going to have it back up and running again thank you so very much, a very instructional video, I loved it & watching you do it as well.
@@stuartukguitarampguy5830 yes, thx I'll need it I don't have any kind of equipment to work with except the soldering gun if I did I still don't know how to read the meters and stuff I'm not Savvy at all but I know how to solder and I know how to replace Parts just which one is wrong which is the bad part I don't know how to do that but from this video I think I'll try that just go to that one and replace it but no Radio Shack anymore so where do I get these parts
Hi Lenn start watching some basic electronics TH-cam vids and you'll quickly learn. I've done a good one on Ohms Law for begginers, that's a good place to start.
I have a VS100 that makes a loud popping noise when I switch it on or switch channels, but doesn't play anything it should. Speaker works. Somebody said it is likely the tube. Any other ideas?
Wouldn’t it have been possible to place a chip socket in there so that if there’s a next time you/us won’t have to do so much disassembly and soldering work replacing the chip should it go faulty again ? If so I’m wondering why the OM didn’t do that at the outset. Any ideas why it failed ? I had someone point out that here are different shapes of Jacks plugs and the jack sockets. Jack plugs that’s come on some leads are slightly different in shape where they mate up with the socket spring and that at the mutual point of contact between the two aren’t making a completely effective contact and as they can not make contact properly after a little use, they stop working after a little wear, it’s hard to spot unless you know to look out for it and unlucky to come across it and don’t look hard at them. Nice viewing, an educational, practical and worthwhile and clearly presented video, thanks very much. It’s great of you to open it up for us and guide us around. Nice tips about the lead labelling for the reverb unit and the signal through a capacitor used as a probe too. I’n guessing a transistor radio or tuner with an output could be used as a sound source for the probe . Any recommendations for an alternative valve, TL072 chip swap, or any other mods ? Maybe a cheap attenuater device for it ? I’ve got an 8080 one that had a nasty bit of noise on turning on mine, but it went away after I’d jiggled about a bit with my lead and knobs. It is Very loud amp for my flat, and I don’t know why the old lady downstairs has to watch so much day time tv, especially there’s so may other things to do. I thought they had signing and sub-titles so why’s she banging on her ceiling with a broom handle, just because she can’ t hear it because of my guitar.
Great job Stu! It's always interesting watching the detective work of electronics fault finding. I just acquired a free but broken 10W 8010 amp which is clockwork in comparison to its big brother Valvestate. When I looked at the circuit diagram I laughed, wondering where all the components had gone. 😂 Edit: I'm a betting man too and my guess without even plugging it in is the MC1458 chip on the input stage. The giveaway is the 3.5mm audio adapter left in the back of the cab, suggesting that it has been thrashed to within an inch of its life. Hopefully it's not the power amp chip... which is RIVETTED in place. Seriously. Why??
Hi Michael Two possibles. If the amp has FX send/return jacks or a headphone jack (I can't remember if it does) then squirt some switch cleaner in and work a jack plug in and out a few times to clean the contacts. If it doesn't have those it could be a power resistor on the main board, these come unsoldered with the heat. Maybe one for an amp tech in that case? If you're comfortable taing the chassis out then power it up and try tapping, wiggling some of the larger components to see if the sound comes and goes. Good luck. Stuart
All the valvestate line of amps have issues with bad soldering and poor design schematics. I had to have a circuit board repaired and he said it was not built well...getting hot, and something to do with the tubes I can't remember but my tech said that was also an issue that was common, might be the one you mentioned? It's all good now. New tubes and some soldering fixed. I had power and sound, but on the acoustic simulator channel(that's channel 1 on these) if I wanted to turn the volume up it would hum and it was a wavy kind of hum that would go up and down and loud and quiet and it was really annoying. I really wanted to use that channel. I have the Big one 2x75 valvestate 2000. It's a heavy beast, but not bad for a 2x12 considering. Problem is it doesn't sound very good turned up to the second slash mark on the master volume. I don't think they put very good speakers in them maybe? Just kinda farts out. I added a big rack mount EQ to the efx loop and that tamed it a bit and helped with the fizz, which was weird because I added more highs. Man it screams. I don't normally turn it up to that second dash mark on the master because that's ear bleedingly loud. Halfway to the first dash mark is plenty loud for practice and up to that mark is great for jamming with a band. I've been told it's too loud a couple times...eh what can you do? lol
@@stuartukguitarampguy5830 I'm no tech, but I've read they are susceptible to low levels of static discharge coming from the input jack. Does that seem plausible to you?
Hi Stuart, I'll be receiving next week a Marshall Valvestate 8080 with a similar symptom, the clean channel is not supposed to work but the overdrive channel allegedly works. I hope it is something similar to the issue you addressed here. I will be using the same "signal injecting" technique (thanks for that), also I found very helpful the explanation about the operational amplifiers, thanks again and greetings from Colombia.
Big surprise. I watched this video last night. I just got an 8280 that I tested today. EXACTLY the same issue. No sound what so ever plugging it in normally. Send/return worked fine. So next step for me, is to swap that chip.
Very nice logic reduction ... reducing or cancelling everything... to the opamp. In real time no less. I like your makes shift signal probe. What was the value of the orange cap. ? Regardless. Very nice job... A magic trick right in front of the audience... for everyone to see. HAH !
Great job stuart. Like your channel just found it and subbed. Quick question? I have a marshall valvestate 40v and was giving a super super loud hum and after diagnosing i found the problem with the ic1 chip tl072 replaces and was fine. Now after about a week of playing it it developed a different problem. After playing gor oh sometime 20 minutes to 45 minutes it starts cutting out and gets worse till i have to shut it off and wait for it to cool down to be ok again. Any ideas for me?? Thanks so much and again like the channel and I hope to see more amp repairs as i have so many vintage classic amps and newer ones as well but some vintage need some restoring and some just maintain clean and freshen up. I believe your never done learning and will click on notifications.Thanks and wish you well. Sincerely, michael
Great Video. Thanks! I´m trying to fix an 80s Fender MIJ Stage Lead II amp. I changed a pot to sort out the reverb, Now there´s a loud POP through speaker when i turn amp on or off - even with master volume turned down. Maybe i disturbed a ground/earth connection when i removed the mother board?? I usually consult Uncle Doug. but he is more a fan of Valves & Horsepower. Hard to find repair videos of Tranny amps! 😁THANKS
@@stuartukguitarampguy5830 Hi Stuart, My mate was happy enough that i fixed the reverb. He mostly uses this amp at home because to the master Volume. POP is reduced if i turn off the power at the long plugboard first. , Mind you an 80s Fender was easier to work on than that BassBreaker you tackled. Thanks for the advise & follow up. Cheers from Madrid
Brilliant! Great to watch on live what is going through your mind and how you make different hypotheses. I have one question: that "tone generator" you use to test the power stage first and every component (with the capacitor) afterwards, is a normal signal generator, am I right? So what voltage level do you set up on the generator? Wouldn't it be risky to plug in a signal with a considerably higher voltage level than what a guitar does? Thank you! And sorry for my english level
Hi Manu Yes it's just a normal signal generator.. If I'm plugging in to the guitar input I usually select about 50mV - 100mV or so. As long as the volume wasn't on max, you could put a much larger signal in and it would just distort, no damage, With all volumes on max and HUGE inout signal, I guess you could just possibly blow the speaker if sustained for too long as it would be very loud, but even that is unlikely.
@@stuartukguitarampguy5830 OK thanks! And in the test where you are using the capacitor do you actually unify the GND of the signal generator with the ampllifier's one?
@@manuaizpuruabakedano Yes the ground of the signal generator is grounded to the amp chassis. Actually most times I don't need to do this as they share a common ground anyway.
Hi Stuart- fantastic video! Thanks! So do you know where to find a COMPLETE manual online for this series? I have an 8280 and it has 4 speaker outputs. The manuals I find online don't have the rear panel illustration so the text references are hard to figure out for that section. The writing on the amp below the output jacks says 100W/4 ohms per channel 80W/ 8 ohms per channel So does that mean its serving up 80 watts with all 4 jacks in use?? and 100 watts with only 2 in use? Does it matter if you use the inside and outside jacks in various combinations or do you have to use inside R and inside L or outside R outside L only for instance? Thanks again!
Hi. Unfortunately there are LOTS of valvestate models. I have a fair few diagrams but if I get one in I haven't seen before I just go online and find it. Most of the scheamtics are out there. I think the 8280 is the 'stero chorus' model isn't it? If so, from memory, it efectovely has two separate power amps (like a Hi Fi stereo amp left and right). So the rating of EACH channel is 100W into 4 ohms or 80W into 8 ohms. So in TOTAL you'll get 200W out of the amp of 160W. You'll need to know your speaker impedance. There are two jacks per channel and the two jacks are wired in parallel. So you ciuld put, say, 2 x 8 ohm speakers in the LEFT and 2 x 8 ohm speajers in the RIGHT and that would give you 4 ohms per channel and yield 100W per channel. Or you could put jut one 8 ohm speaker in one of the LEFT sockets and another 8 ohm speaker in one of the RIGHT sockets and you'd get 2 x 80W. Does that make sense?
Beautiful work sir , I still have my Marshall Valvestate VS100 laying around , abandoned it years ago after it wasn't giving any guitar output , all it does when you turn it on is crackle & pop , loud as hell , the Power Module board is 100% fine , I'm pretty sure its the preAmp , but I had "amp technicians" reject it , and I bet you would be able to easily fix it
Good job! I like that signal bypass thingy you used to help you diagnose the problem. Would using a surge protector help the operational amplifiers to last longer?
Hi Zak, no a surge protector would not give any additional protection to the op amps. They come from their own smoothed supply. Nice thought though! It's just an age thing, after many years some of them fail. When you think what's inside them....
Hi Stuart, an update on my 40 watt Hiwatt amp. Used your technique of poking board with a stick, looked for signal using tone generator app on my phone
@@stuartukguitarampguy5830 Happy to report amp is working fine. I had to replace 2 op amp chips. Couldn't find exact ones but found alternatives. I'm no electronic wizard, but following your methodology worked a treat. Many thanks!
That was fun to watch and informative. I have a VS100 I got in 1994 that's giving me issues. A few years ago the valve was blown but now it's intermittently working. I did notice that if I whack the top of the amp it'll come alive for a moment and then go out. I don't think it's a bad op-amp like yours was. From what you said, it sounds like dry joints might be the culprit? I'm a hobbyist with electronics so I am familiar with soldering but I really wanted to avoid removing the board. I might have a go at it. These amps are cheap now but it's got a lot of sentimental value for me plus I think it sounds nice. :)
Having the same issue as you. Also a beginner hobbyist and have been building my own pedals (kits with ready made PCBs), so I can definitely solder/reflow cold joints. I’d have no idea where to look though... tempted to just give it to a pro, on the other hand also tempted to fix it myself...
@@jonathanonguitar The most common problem with valvestates is dry joints, particularly around power resistors. If you are interested in repairing amps etc I'd encourage you to have a go because this is exactly how you learn. All amp techs have their 'first amp' they ever worked on. It's a learning curve and the only way is experience built one amp at a time. I've repaired thousands (literally) of amps and hardly a day goes by when I don't come across some new problem which challenges me. So it never stops! Have a go. Get started. Get a schematic and start trying to understand it. Also, there are some awesome resources out there these days. My videos, Uncle Doug, The Guitarologist etc. Experts walking you through amp after amp. Didn't exist 20 years ago. Heck you couldn't easily get schenatics 20 years ago!! Good luck!
@@stuartukguitarampguy5830 My son's amp was cutting out recently. It's a 20 year old Crate amp. I finally pulled the board after ruling everything else out. Armed with some knowledge gained here, I found a couple of cracked joints. I resoldered them and _so_ far, so good. I had retired my Marshall a while back before I could repair it. Now that I've gotten my feet wet with pulling a board out, I'll take the plunge. Great resources of knowledge here! :)
Nice video, Stuart. I’m forced to try this for myself, but have no knowledge of this kind of thing. Mostly I’m abit worried about getting electricuted. Any tips on what to stay away from? Greetings from Denmark
thanks for this video. I had a question for you. I have a Rocktek RK20R. The amp is very loud but the sound is muddy and too saturated. The tones are not clear and can't hear the characteristic sounds of my strat and tele. I plugged it into a stereo and the speaker is perfectly clear in playing radio music. All the cords are good. I think the issue is the sound processing in the pre amp part. Can circuit problems make the sound muddy and overstaturated? or is it just a poor amp. I wanted to see if it's worth going through all the circuit board looking for problems. I've played with all the setting for several hours to no avail. Thanks sir
Hi Stuart. I've raelly enjoyed your videos on fixing up old Marshall Valvestate amps. I just bought an old Marshall Valvestate 8100 head that is in dire need of some maintenance (I only payed the equivalent of 50£!). I'm fairly sure it's just the pots that need a good cleaning. I am however in doubt if there are any high voltage filter caps in the amp that I have to look out for? Or are these only used in "true" valve amps with valves in the power section? I'm still very much a novice when it comes to electric circuits and the likes, but I'd love to learn how to maintain, repair, and perhaps even mod guitar amps when my knowledge and skills allow.
Hi There are HV caps in this amp but they are not very large and will quickly discharge. Ideally get the board into a position where you can see the underside. They suffer badly from dry joints particularly around the larger caps and power resistors. reflow all these. Clean the pots. Might be good to go?
Hello Stuart, do you know where to get a transformer for the Valvestate amps? I have an 8040 from the USA which has the 120v volt PT. It seems there are no other taps on the transformer to use for 230v. Any ideas? Thank you for an interesting video.
@@stuartukguitarampguy5830 literally since 3h I’m watching yours videos, the simplicity and engagement and honesty that you convey.. awesome!!! Surely it started as I’m having some work to do on my amp Marshall vs 8240 but I know now much more. Thank you Sir! And I know how much time it gets to document things… as a content creator I know. It would be so much easier just to make things done, but record it, explain, put it together… takes sooo much rime and additional effort. But you teach us, we appreciate it.
I gave my dad a Boss Katana amp that he's been very happy with, and he gave me his very poorly Valvestate S80, because I've always quite loved the Valvestate clean tones. It sounds very different than any of the famous classic tube amps, yet I don't think it sounds sterile at all. I hope some of this will help me getting it in shape. The main problem though, is that the beautiful spring reverb jumps in and out whether it's turned on or off. Any suspicion what it might be?
I have a Valvestate 8040 that I bought new in 1992. It’s had a few minor repairs including bypassing the Pre-amp jack around 10 years ago which fixed a faulty jack socket (I didn’t use this facility anyway so was easier to delete it). I also replaced some of the scratchy pots (although cleaning them would have been easier!) My amp was unused for 4 weeks whilst I was holiday and on return, there is almost no sound. The spring reverb works (you can hear when tapping on the tank) and when I plug into Power-amp IN, I get sound. I replaced the 12AX7 with a new one (I assume the new one works) and no change. I’ve checked for dry solder joints and have refreshed a few joints. There is some sound on full volume on the clean and boost channels but not close to normal. There is also a noticeable hum at high volumes. Any advice? I suspect an Op amp chip but I don’t have equipment to check them.
Hi It's SO difficcult to diagnose these things over the Internet. They are very prone to dry joints on the larger caps and power resistors, so maybe check that (waggling the component can cause the sound to suddenly come back). I can;t recall if this has FX send and return jaccks. If it does, clean those. Good luck!
Thanks Stuart. There is no FX loop in this amp. I’ve been over all the solders looking for dry joints but I will specifically check the power resistors and caps.
Hi Stuart I’m fairly certain that it’s not a dry joint. I am getting sound on the boost channel but it’s noisy (lots of hum). On the clean, there’s almost nothing except at full volume. I definitely think that it’s a component in the pre amp stage. Can I test the op amps with a signal from my guitar similar to your technique in this video? I’m based in the Middle East so limited for options with repair. I think that I will be able to find replacement TL072s though.
@@darcycuttlefish3981 Hi Darcy Ok you've tripped my memory. I have changed MANY TL072s on these amps. It won;t be easy for you to diagnose without a scope. You could just swap out the first two chips and hope that cures it.
@@stuartukguitarampguy5830 I think that’s what I’ll do. Op amps do seem to be cheap so little to be lost. If that doesn’t work then I’ll think that I’ll get a new amp as the alternative is to transport amp back to UK to repair and that’s not worth the trouble.
Hello. I have the same model at home. I have some problems with it. The two speakers work separately if put the jackstick in from the back. I cant make the other ports work(i have only tried with jacstick from my phone, not a guitar) and if i turn the volume up and down it makes a lot of loud noices. To me it sounds like a loose connection, but i would like to get an other opinion and ofcourse know if it's worth the time and money it will take to fix it. I really hope you will answer. Regards Mark
Watching this because I have an 8080 valvestate and the normal channel volume is low and reverb does not work. Boost channel is fine. Tested reverb leads and tank, both test out ok.
Hi Hard to diagnose over the internet. 90% of time with reverb it's the tank or leads. VERY rare for it to be something else. If you have a meter you can test both sockets on the tank. Open circuit means it's bad. Low ohms means it's good. On the low volume it MAY be one of the op amp chips but honestly it's so hard to say. Good luck!
Hi William. Well this one isn't easy to fix if you have NO knowledge of electronics, plus those darn 8 pin chips are a little tricky to get out. This is probably one for an experienced amp tech. I you do have a go yourself unplug the amp leave it for an hour or so before working on it.
I often wonder, when an amp has two channels, and is rated at 100 RMS (I have a 2 channel 100 RMS Hartke GT 100), is it two discrete channels all the way through to the power stage, which would mean it’s really only 50 RMS when you plug into one or the other channel, or is it two preamps fed into one 100 RMS power amp? Thinking back to a Sears Sivertone two channel tube amp I once had (unfortunately lost track of), that used four 6L6 power tubes. Rated at 100 watts (not sure if that’s RMS), driving six 10 inch Jensen speakers. Too late to look now, but of course I could have answered the question by looking to see if there were two audio output transformers. I see two channels on the amp you just gave a second lease on life. Is that two preamps, fed into one power amp? Curious what is the RMS if you happen to know it as well. Thanks!
Hi. The power amp is rated at, say, 100W so the amp will give out 100W. Two channels are separate preamp channels feeding into the same power amp. Does that help? Bottom line, 100W no matter which preamp you use.
@@stuartukguitarampguy5830 Got it! I was so used to thinking of 2 channels as stereo, left and right, from input to power output. Though I still don’t understand why a guitar amp would have 2 separate preamp channels, feeding the same power amp, especially when you can only use one or the other, not together at the same time.
Hi. The usual reason to have 2 or even 3 completely separate preamp sections is so that you can dial in completely dfferent sounds on each and then just kick a footswitch to change between them. The most common setup is to have a 'claen' channel' and a 'drive' channel. One click and you ggo from country and western to full on metal!@@user-qm7nw7vd5s
@@stuartukguitarampguy5830 I see! So that’s what that foot-switch is for (that I kept rolled up and tucked inside the cabinet, so as not to lose ). THANKS!
Hi Stuart, I have Marshall AS80R which gives crackling noises when powered on. I have looked a the circuit boards and I found no bad solders or burnt components. What is common problem with this amps? Mine is about 15 years old and it was working until it was stored away a couple of years. Appreciate your advice at what I should to fix the problem.
Hi Jay I can;t recall if this model has FX and/return jacks. If so try cleaning those. Also turn all the controls back and forwards full range about 10x each to clean the tracks a bit. Other than that you'll need a tech. All the best.
Would you have an idea why the effects might have stopped working on my amp ? It is a Marshall AVT150X. It has multi effects - delay, chorus, flanger etc that were all going fine until yesterday. The amp itself seems ok , problem seems to be from the presence right through the effects mix, selector etc.
Hi Stuart, I have a Marshall DSL20CR ( a year old), and I flipped the stand-by switch from 20 to 10 amp. while it was in play mode.Now I only get very faint sound when I try to play it. I've ordered new tubes.Do you think the tubes are the problem? Thank You.
I;m not familiar with that amp as it is quite new. When yousay 10 amp do you mean 10 watts? It's unlikely the tubes have gone after a year but since you have ordered them anyway you may as well try.
Yes I did mean Watt.There's a switch right beside the " Power " switch.' Up " is 10 watt, middle is " stand-by, and down is 20 watt.I flipped the switch from 20 to 10 while the power was on.@@stuartukguitarampguy5830
Hey Stuart, I came across your awesome video because I'm trying to fix the amp (Marshall Valvestate 40V Model 8040) my brother gave me. I made a reddit Post with a video showing what I think is wrong with this amp. Sadly my comment gets deleted when I write out the link. Is there a way I can send you the link? Here is the text I wrote: Hey, my brother gave me his old amp, since I recently started playing guitar. He said I can try to fix it and that the gain and volume knobs are the problem. But I guess there are more problems, since the crackling sound and this periodically appearing knocking sound are always present. In the video you can hear what happens when I'm turning the volume knob of the boost channel. The volume knob doesn't work smooth at all and sometimes there is this low cut happening. The other knobs do something but this is my first amp so I don't really know what sounds to expect. Moreover, sometimes there is this reverb coming through without it being turned on. I am an electrical engineering student and I want to learn a thing or two, since my studies are mostly theoretical. Best Regards Finn
Hi Finne. Yes it's annoying, TH-cam delete any comments which have a URL in them. Maybe it's to stop spam or something. If you go to the very end of any of my videos you''' see an end screen and on there is my website address, you can contact me via that. You amp seems to have a large number of different problems. The first thing I would do is remove the board and check for dry joints as these amps are VERY prone to them. In fact I've never seen one which didn;t have a load of dry joints. Stuart
Clean all pots and switches with DeOxit D5. If that doesn;t cure it you'll need to remove the board, it will almost certainly have dry joints on it. Good luck.
Hi Stuart, I have a fender 15g frontman and the volume level is at a level 2/3 no matter how high or low you turn the knob. Whether you raise the volume knob to 10 or to 0 it stays at the same volume which I would say is about a 2/3.. the drive volume works but not the normal volume. What do you suggest?
@@stuartukguitarampguy5830 No - mine is on the top bolted to the amp (horizontally - yours was vertical. As you said, there were many variations of this model.)
It's always a difficult choice to repair these amps. I have an 80 watt Valvestate which cuts in an out and the cost to repair it would outweigh its value but then you have an emotional connection with these old things.
Hi Mark That will probably be a dry joint. If it was me I'd the chassis and have a gentle wiggle of some of the power resistors etc. see if you I find it. I canlt recall if this has FX sned/return jacks. If so, try cleaning those also.
Nice video, BUT.... ALWAYS.... ALWAYS pull the board out to look for cold solder joints/broken joints. I just repaired a VS232 that had no visible anomolies until I realized the input has an open connection at the input, so it took a new input jack, and good as new.
Please, how much watts each speaker have? I got that they are phisically same as g12t-75, but this is stock version...without numbers :)..only "g12t"....so are they 2x75 watt or?? THX
Hi Stuart. I was just wondering if you offer any valve testing services? I have a box of old Soviet EL84s and I simply want to know which ones are ok and which ones to bin. Thanks!
Hi Stuart, I hope you're doing great, Do you have an advice about an amp I have, this is a Marshall Valvestate AVT20, the thing is that it doesnt bring any sound, I thought that the bulb was the problem but I just got a new one but is still mute, I noticed that the clean\od button light doesn't respond when I turn on the amp, maybe there is the problem, do you know what might be the problem with this amp? Thank You in avance :)
If the clean/od button does nothing then I suspect it's a problem with the low voltage (+/- 15V from mempry) power supply. You'll ned to find a tech to look at it.
Hi Stuart, awesome work, glad you got it sorted. I have a similar problem with my VS100, turn it on, almost no sound, you hear the guitar pretty low almost inaudible. Do you have any ideas what could it be? Thank you
Hi. Always hard to diagnose such things at a distance, but if you have an FX SEND/RETURN jacks then try cleaning those with contact cleaner (just spray it in through the hole, no need to take the amp a[art) and work a jack plug in and out a few times. That is a common problem on all amps with these jacks.
I have the 8280 bi chorus and only can use the left output speaker but the right output is death and i dont know how to fix it 😓 both speakers are ok but i feel bad for not find a way to fix without help from a tech.
Hi. From memory the bi-chorus uses two audio amplifier power chips, one for each channel. So I expect one of those chips may have gone down in your amp. Not an easy replacement I'm afraid. The chips aren;t that expensive though.
@@stuartukguitarampguy5830 Thanks for the reply. I understand that I will not be able to do the repair on my own but I have already contacted a tech to help me repair it. I have the kinematics and I hope with that it will be easier to identify the piece to change. Greetings!
Stuart, I just picked up a Valvestate 8040 40 watt with 1 x 12” Celestion. The symptoms were the same as the Valvestate in your video, power up but no sound. The previous owner said he took it to Guitar Center here in Texas, and they told him there was a problem with the board, so he bought a new amp from them. I just got the amp home, plugged it in and moved the amp, and what did I hear - loud reverb spring noise. There is no sound when I plug in the guitar into input. But when I plug the signal out from my Tascam portable guitar trainer into the preamp in, I get a strong signal, when I plug it into the guitar input I get a lower volume signal, and the sound gets louder when I increase the gain, so it’s not the jack. Do you think it could be the valve? Or would it be an op amp, What are your thoughts ?
Tricky to diagnose over the Internet. The valve is dead easy to change so start with that just to eliminate it. The power amp is working fine so it's a preamp problem. Could be an op amp 50/50. I would have thought any halfway decent amp tech could sort this for you fairly easily.
I pulled the chassis and changed the tube for a new one, no change in the symptoms. I then tried something I had read somewhere, I plugged a patch cable into the pre amp out and the other end into the power amp in, I plugged in my guitar, and to my surprise I had a nice clean and loud signal from both channels. I tried cleaning the input jacks with Deoxit and strips of paper. I ordered some replacement jacks, so next step I will remove the PCB and check the solder joints or replace the jacks.
Yes those jacks are a constant source of trouble on ALL amps whuich have that arrangement. I'm surpirsed that cleaning them didn;t do the trick though, as it sorts it in 99% of cases.
@@stuartukguitarampguy5830 i had a faulty connection on the power amp in jack, I replaced the jack, and it cured the initial problem. Now I have another issue it’s making some strange sounds with no cables plugged into it, I turn it on and turn the controls up on the clean channel and can hear what sounds like a rain shower. When I turn the boost channel on I start to hear a squeal when the gain gets close to 5 and it gets louder from there. I have attached a link to a TH-cam video: th-cam.com/video/4o3sqppYhy0/w-d-xo.html&feature=share
@@cliveblowers709 Hard to diagnose these things over the net. You have a VERY high level of gain dialled in there so you will get some hiss. It could be one of the op amps going noisy. The high-pitched squeal you are hearing is the amp going into oscillation. Sorry I can't really help more than that without seeing it.
I'm not familiar with those Integrated power amplifier SIPs. Does anyone know enough about them ? Who makes this type of IC: They certainly take some massive heat sinks, don't they !
Hi Stuart. I am very interested in the signal generator testing method. I could also give in an audio signal out of my phone (played song, signal generator app) right? Also: what are the specs for the capacitor you´re using if you don´t mind me asking?
@@stuartukguitarampguy5830 Thank you for your fast reply! I might have read 0.1 on the capacitor one moment in the video but it was hard to read really. Does the type of capacitor or it´s value matter too much?
@@el_micha Value not critical. You do need something with a decent voltage rating though (400V or more) as you will be sticking one end of it on various places which might have a few hundred volts floating around!
I have a question if you could please help me out on this. I have a 1972 U-400G Univox 35 watt guitar amplifier that I believe has the same problem but I cannot find a replacement chip. The op amp chip number is 8022A and it seems to be not in production anymore. Do you know of a replacement number I could try? Thank you, Charlie
Hi Charles. Hmm, I see what you mean, that's quite a rare op amp and quite a fancy one from Analog Devices. I wonder why they used that chip. Is it surface mount or regular through hole? I Guess all you can do is do what I'm doing - Google searches etc. I don't have any inside info.
@@stuartukguitarampguy5830 Hi Stuart thanks for your reply. The chip is an 8 pin through hole chip. I wasn't sure if you knew of a replacement? I found some that have the same number (8022) but have a different prefix (AP8022). They are surface mount but I could make it work by soldering it to the legs (that I would leave on the board) of the old chip but was not sure if it would work or not, what do you think? Thanks again!, Charlie
@@stuartukguitarampguy5830 Thanks again Stuart, do you know of a supplier that I could buy one or two of them? I've only found suppliers that sell them in quantity (1000 + etc.). I live in the U.S. Thanks again, Charlie
I have a single speaker AVT 50 w valvestate. Same issue as the one in this video, I have a small dc voltage on the amp chassis when switched on. Any thoughts? Also wher do you buy the replacement op amps please?
Hi Cary EBay for the op amps. Loads of people sell them. From what reference point are you measuring the DC voltage on the chassis? Also, what is that voltage?
@@stuartukguitarampguy5830 thanks. I am getting 2 to 3 volts. I do use a multi meter at work but no expert, I was using an earth separate from the chassis and by touching the chassis with the live probe I get the reading. I may be doing something wrong?
@@gashead2 Hi Cary. Can you check with one probe on the earth of the mains plug and one on chassis and also make doubly sure you're reading volts not millivoilts. If you still get 2-3 volts you need to check the ground connectiomn from the mains lead to the chassis. I'm not 'wrried' by the 2-3V but the chassis should defo be at ground.
@@stuartukguitarampguy5830 I haven’t checked the voltage yet but I thought I would do earth continuity first. I am getting continuity between the earth on the plug and the black and red wiring on the 24v side of the transformer? Also the amp has a jack plug to connect the speaker, all of the other jack sockets show continuity to earth on one side of the jack but the speaker jack socket does not show any. I have looked at the pcb where the speaker jack is and there are no signs of distress. The amp chassis shows good earth continuity of less than 1 ohm. Any help appreciated, the amp belongs to my grandsons school and I was hoping it was dirty pots! I have tried a new valve too, thanks.
@@gashead2 Hi Cary TWo things. Forstly you won;t have any earth continuity on the speaker jack. Both contacts go to the output transformer secondary, which is not earthed, so your test on that is ok. Nothing more to do. I was unclear what you meant by the '24V side of the transformer' Do you mean a 24v AC winding? I don;t think you should be getting a reading to earth on that side of things but it's so hard to know and there's a limit to what we can do by email.
Hi John I'd love to help but it's almost impossible to diagnose something from a distance. It could be many things. Obviously check fuses and speaker connection. Sorry I can;t do more.
@@stuartukguitarampguy5830 thankyou Stuart for the reply and video,I am glad to say I have found the cause today simply the speaker was not working,should have realised this as there was no sound or hum,wish I had checked this before striping it all down,you video was very helpfull
It’s awesome that people like you Sir are still around, helping people enjoy their old amps. They are certainly worth it. Have a great day
Thanks!
Most techs won't even take in a solid state amp. The repair cost exceeds it's value so good on you for doing it for a nominal fee. I'd pay your price for the simple fact that if I like the amp I'll pay to keep it alive.
Yes I'm not super keen on solid state stuff I'll admit.
You should make instructional videos for everything. Clear, concise and doesn't get you confused with needless conversation. Excellent video!
Thanks Mike!
Good video tutorial. I have fixed loads of Valvestate amps myself. Most of the issues are caused by broken solder joints on the jack sockets, oxidised contacts on the send/return loop, oxidation/dirt on the first gain control and of course that first TL072 chip which is the fault you found here. The chip is knocked-out by static from guitar leads and stray voltages from guitar pedals. It gets noisier as time goes by and eventually dies. Later Valvestate amps have better protection circuitry on the input jack. It doesn't help the way the first gain stage is wired-up on some of these amps. Instead of using a fixed resistor in the feedback loop on that opamp, Marshall have worked the variable resistor in there instead. Dirty contacts on that control sound terrible!
Excellent and informative video Stuart . I fully understand your work ethics being a
retired (71) electrician. I:m more than happy to do small works for small,ish
rewards. Still enjoy the buzz... Cheers and keep up the good work.
Thanks Graham.
Stuart, I enjoy it when you do the live thing when troubleshooting. The talking through the process is valuable to someone with my level of knowledge. Learning how to think is a wonderful activity and is exacty why i began this journey. I truly appreciate your ability to make it understandable.
Mike
Thanks Mike.
29:01 The ubiquitous cup of tea. Fuel for every mechanic, techie and engineer in the UK. Bravo sir!
i love the way you did this. Doing it live. It's a ""who dun it" for people like me who love this sort of thing. Fascinating. Thank you.
I really appreciate your videos. They are both informative for specific problems, but also show an effective approach to problem-solving. I have learned a lot of practical techniques from you in a short time indicating to me at least, the effectiveness of your videos. Thanks very much!
Excellent thanks Jim.
Nice to have the thinking behind the troubleshooting process explained clearly. I have a small Marshall amp where the sound suddenly cuts out when in use and it's given me ideas of where to look for problems that are within my ability.
Excellent. Good luck!
Fine job and I appreciate your diagnostic methods. As an auto technician now retired I was taught the same way. Positive test everything you can to make a determination.
Thanks Larry.
Years ago, I had a 100w valvestate head and a 4x12 cab which served me for a 1000 gigs and never let me down. The sound was superb. Then I became a pro guitarist and thought I needed expensive gear so I bought many various amps including Mesa, soldano etc but they never could produce that sound I got from a £300 rig! I really miss that amp!
Hi Paul YEs those amps have a really great sound but they are not very well made and are prone to (easily fixed) problems.
Very nice. I've bought many amps for cheap that were heading for the bin. In 95% of cases all the amps needed was a good jack cleaning (sometimes the finger switches are bent) and one or more cold solder joints.
On the one hand I hate that people have such a disposable mindset that they would throw away an amp instead of fixing it, but on the other hand, if they fixed them then I wouldn't get perfectly good amps for pennies on the dollar. I just bought today this same amp, the VS580 for $35. Nothing wrong with it except a broken fuse holder.
I think they simply don't know how to fix, or know anyoine who can. The amp's been in the loft for 15 years
and they just want rid. Your gain, as you say!
Lovely repair. I bought a vs100 for 100€ which the seller said it had a strange noise. The thing was oscilating because of cracked solder joints. Got that fixed. It still has a bit of a hum, mostly when its heating up the valve. Thanks for the video.
Nice one. You got a bargain there!
Wow! You’re certainly thorough! My 65r valvestate had the same issue so I gave it away. Loved that amp as well!
Hi Stuart, I enjoyed this fix. It might be worth keeping a small journal with model names and what the issue was. Easy to flick through when you receive more work. I'm aware yes it is already on film, just thought it might be easier to get the data you need.
Thanks Otto. As you might guess I already have a substantial spreadshet containing full details of the several thousand amps I have repaired. Suprisignly, it rarely comes into play to help diagnose a new issue. Stuart
Excellent work Stew. Many thanks for posting. Took me back forty-odd years and my training in fault-finding when an apprentice electrician. We actually trained on valve amps etc. Sadly I never stuck at it. If only I knew then what I know now.
Thanks for the heads-up on the Duratool de-soldering station Stuart, just bought one for my hobby workshop.
Great piece of kit and there's nothing else out there even remotely similar in price.
Don't know how I missed this one. I have worked on this same breed several times, and every time so far, the same culprit. I think we may need to stock up on ic sockets, or design a conversion to a ecc/12ax7 :) Keep them coming always Stu. And always enjoy going on the ride with you.
If you are interested in old rotten cars being resurrected, hope you will pop into my new series of videos. I could use as many subscribers as I can get to get off the ground.
Thanks. No, old cars aren;t my thing at all. It's quite a slow burn building up subscribers from scratch but if the content is good, you'll steadily add people. Forget about monetising the channel though - almost impossible these days.
Hi Mark. One way to rest for loose connection or dry joint is to play some music through it (e.g. from your phone) then give the amp a couple of sharp bangs on the top with your fist. If you hear loud crack when you do this, or sound comes/goes it's defo a dry joint etc. Other than that, an amp tech should be able to sort it for you.
thanks for the answer
Nice fix Stuart, like the walk thru and your clever tricks and methods to find the problems..Great learning experience for us newbies..Thanks again for sharing..Ed..uk..😀
Thanks for your positive comments as always Ed. Stuart
Thanks Stuart. You've inspired me to fix my old Valvestate 8040 which has scratchy pots. The bass control doesn't work either - Yet!
Go for it!
I have the Marshall stereo valvestate vs265 and it has the chorus 3-channel stereo, clean, overdrive one, overdrive 2 & overdrive EQ as far as any name goes with this it just says valve state Vs265.
Anyway I have saved this video and I'm not really an electric technician but I love electronics, I can troubleshoot a little bit but I'm going to fix my amp, its been my favorite amp, & thanks to you I'm going to have it back up and running again thank you so very much, a very instructional video, I loved it & watching you do it as well.
Hi Lenn. Glad you enjoyed the vid. Good luck fixing your amp!
@@stuartukguitarampguy5830 yes, thx I'll need it I don't have any kind of equipment to work with except the soldering gun if I did I still don't know how to read the meters and stuff I'm not Savvy at all but I know how to solder and I know how to replace Parts just which one is wrong which is the bad part I don't know how to do that but from this video I think I'll try that just go to that one and replace it but no Radio Shack anymore so where do I get these parts
Hi Lenn start watching some basic electronics TH-cam vids and you'll quickly learn. I've done a good one on Ohms Law for begginers, that's a good place to start.
@@stuartukguitarampguy5830 thx stuart
I have a VS100 that makes a loud popping noise when I switch it on or switch channels, but doesn't play anything it should. Speaker works. Somebody said it is likely the tube. Any other ideas?
Hi It won;t be the tube. However it could be many, many other things so you'll need a tech I'm afraid.
@@stuartukguitarampguy5830 Nah, lots of other things I can check myself before paying someone more than the whole amp is worth.
Excellent video. Those amps are fantastic. I've a loan of a AVT 150. it is a monster.
Thanks glad you enjoyed it
Wouldn’t it have been possible to place a chip socket in there so that if there’s a next time you/us won’t have to do so much disassembly and soldering work replacing the chip should it go faulty again ?
If so I’m wondering why the OM didn’t do that at the outset. Any ideas why it failed ?
I had someone point out that here are different shapes of Jacks plugs and the jack sockets. Jack plugs that’s come on some leads are slightly different in shape where they mate up with the socket spring and that at the mutual point of contact between the two aren’t making a completely effective contact and as they can not make contact properly after a little use, they stop working after a little wear, it’s hard to spot unless you know to look out for it and unlucky to come across it and don’t look hard at them.
Nice viewing, an educational, practical and worthwhile and clearly presented video, thanks very much.
It’s great of you to open it up for us and guide us around. Nice tips about the lead labelling for the reverb unit and the signal through a capacitor used as a probe too. I’n guessing a transistor radio or tuner with an output could be used as a sound source for the probe .
Any recommendations for an alternative valve, TL072 chip swap, or any other mods ? Maybe a cheap attenuater device for it ?
I’ve got an 8080 one that had a nasty bit of noise on turning on mine, but it went away after I’d jiggled about a bit with my lead and knobs.
It is Very loud amp for my flat, and I don’t know why the old lady downstairs has to watch so much day time tv, especially there’s so may other things to do.
I thought they had signing and sub-titles so why’s she banging on her ceiling with a broom handle, just because she can’ t hear it because of my guitar.
Great job Stu! It's always interesting watching the detective work of electronics fault finding.
I just acquired a free but broken 10W 8010 amp which is clockwork in comparison to its big brother Valvestate. When I looked at the circuit diagram I laughed, wondering where all the components had gone. 😂
Edit: I'm a betting man too and my guess without even plugging it in is the MC1458 chip on the input stage. The giveaway is the 3.5mm audio adapter left in the back of the cab, suggesting that it has been thrashed to within an inch of its life.
Hopefully it's not the power amp chip... which is RIVETTED in place. Seriously. Why??
OMG. Good luck with that!
Nice troubleshooting, Stu. Very nice.
Hi Michael Two possibles. If the amp has FX send/return jacks or a headphone jack (I can't remember if it does) then squirt some switch cleaner in and work a jack plug in and out a few times to clean the contacts. If it doesn't have those it could be a power resistor on the main board, these come unsoldered with the heat. Maybe one for an amp tech in that case? If you're comfortable taing the chassis out then power it up and try tapping, wiggling some of the larger components to see if the sound comes and goes. Good luck. Stuart
All the valvestate line of amps have issues with bad soldering and poor design schematics. I had to have a circuit board repaired and he said it was not built well...getting hot, and something to do with the tubes I can't remember but my tech said that was also an issue that was common, might be the one you mentioned? It's all good now. New tubes and some soldering fixed. I had power and sound, but on the acoustic simulator channel(that's channel 1 on these) if I wanted to turn the volume up it would hum and it was a wavy kind of hum that would go up and down and loud and quiet and it was really annoying. I really wanted to use that channel. I have the Big one 2x75 valvestate 2000. It's a heavy beast, but not bad for a 2x12 considering. Problem is it doesn't sound very good turned up to the second slash mark on the master volume. I don't think they put very good speakers in them maybe? Just kinda farts out. I added a big rack mount EQ to the efx loop and that tamed it a bit and helped with the fizz, which was weird because I added more highs. Man it screams. I don't normally turn it up to that second dash mark on the master because that's ear bleedingly loud. Halfway to the first dash mark is plenty loud for practice and up to that mark is great for jamming with a band. I've been told it's too loud a couple times...eh what can you do? lol
Hi Neil yes you're right they ALL have this bad soldering etc issue. Interestihng about your 2 x 12!
Excellent! Thank you for filming. That particular op amp seems to be famous for giving up the ghost on these Valvestates.
Yes I have changed many. It would be fascinating to know EXACTLY what goes wrong at the micro level to cause them to fail.
@@stuartukguitarampguy5830 I'm no tech, but I've read they are susceptible to low levels of static discharge coming from the input jack. Does that seem plausible to you?
@@divebomb99 Interesting. I'm wondering though as I'm pretty sure I've replaced these in various positions in the chain, not just the first one.
Hi Stuart, I'll be receiving next week a Marshall Valvestate 8080 with a similar symptom, the clean channel is not supposed to work but the overdrive channel allegedly works. I hope it is something similar to the issue you addressed here. I will be using the same "signal injecting" technique (thanks for that), also I found very helpful the explanation about the operational amplifiers, thanks again and greetings from Colombia.
Hi Santiago. kay let's hope you find it fairly easily.
Looks like there would be be a way too modify the chassis for future service,, too access the circuit board.. Great video content.
Thanks Jean
I bought a vox vt30 for £30 all it needed was a new valve and a volume pot amazing sounding amp for not much money :)
Wow that's a bargain!
Big surprise. I watched this video last night. I just got an 8280 that I tested today. EXACTLY the same issue. No sound what so ever plugging it in normally. Send/return worked fine. So next step for me, is to swap that chip.
Wow let's hope it sorts the issue. Good luck.
That signal injection trick is genious. What capacitor should be used there?
Not super critical. 100nF at 500V would be fine.
excellent dig mate!
Cheers!
Great job Stuart. I enjoyed it very much 👍👍
Very nice logic reduction ... reducing or cancelling everything... to the opamp. In real time no less. I like your makes shift signal probe.
What was the value of the orange cap. ?
Regardless.
Very nice job... A magic trick right in front of the audience... for everyone to see. HAH !
Thanks Williajm/ I think it was a 0.1uF cap. Almost anything will do thought, not too critical.
Really good video, nicely taliked through. Well done.
Many thanks
Great job stuart. Like your channel just found it and subbed. Quick question? I have a marshall valvestate 40v and was giving a super super loud hum and after diagnosing i found the problem with the ic1 chip tl072 replaces and was fine. Now after about a week of playing it it developed a different problem. After playing gor oh sometime 20 minutes to 45 minutes it starts cutting out and gets worse till i have to shut it off and wait for it to cool down to be ok again. Any ideas for me?? Thanks so much and again like the channel and I hope to see more amp repairs as i have so many vintage classic amps and newer ones as well but some vintage need some restoring and some just maintain clean and freshen up. I believe your never done learning and will click on notifications.Thanks and wish you well. Sincerely, michael
Super troubleshooting job. Great video my friend.
Thanks Monty!
Great Video. Thanks! I´m trying to fix an 80s Fender MIJ Stage Lead II amp. I changed a pot to sort out the reverb, Now there´s a loud POP through speaker when i turn amp on or off - even with master volume turned down. Maybe i disturbed a ground/earth connection when i removed the mother board?? I usually consult Uncle Doug. but he is more a fan of Valves & Horsepower. Hard to find repair videos of Tranny amps! 😁THANKS
Hi Dan It's very hard to diagnose faults without seeing the amp I'm afraid. Did you make any progress?
@@stuartukguitarampguy5830 Hi Stuart, My mate was happy enough that i fixed the reverb. He mostly uses this amp at home because to the master Volume. POP is reduced if i turn off the power at the long plugboard first. , Mind you an 80s Fender was easier to work on than that BassBreaker you tackled. Thanks for the advise & follow up. Cheers from Madrid
Thoroughly enjoyed that, thank you 😊.
Thanks Hugh
I'd be tempted to socket that TL072, as long as I was in there.
That was fun Stuart. Thank you.
Glad you enjoyed it.
Brilliant! Great to watch on live what is going through your mind and how you make different hypotheses.
I have one question: that "tone generator" you use to test the power stage first and every component (with the capacitor) afterwards, is a normal signal generator, am I right? So what voltage level do you set up on the generator? Wouldn't it be risky to plug in a signal with a considerably higher voltage level than what a guitar does?
Thank you! And sorry for my english level
Hi Manu Yes it's just a normal signal generator.. If I'm plugging in to the guitar input I usually select about 50mV - 100mV or so. As long as the volume wasn't on max, you could put a much larger signal in and it would just distort, no damage, With all volumes on max and HUGE inout signal, I guess you could just possibly blow the speaker if sustained for too long as it would be very loud, but even that is unlikely.
@@stuartukguitarampguy5830 OK thanks! And in the test where you are using the capacitor do you actually unify the GND of the signal generator with the ampllifier's one?
@@manuaizpuruabakedano Yes the ground of the signal generator is grounded to the amp chassis. Actually most times I don't need to do this as they share a common ground anyway.
Wow! That was quite interesting! Many thanks for sharing!
Thanks Martin
Hi Stuart- fantastic video! Thanks! So do you know where to find a COMPLETE manual online for this series? I have an 8280 and it has 4 speaker outputs. The manuals I find online don't have the rear panel illustration so the text references are hard to figure out for that section. The writing on the amp below the output jacks says 100W/4 ohms per channel
80W/ 8 ohms per channel
So does that mean its serving up 80 watts with all 4 jacks in use?? and 100 watts with only 2 in use?
Does it matter if you use the inside and outside jacks in various combinations or do you have to use inside R and inside L or outside R outside L only for instance?
Thanks again!
Hi. Unfortunately there are LOTS of valvestate models. I have a fair few diagrams but if I get one in I haven't seen before I just go online and find it. Most of the scheamtics are out there.
I think the 8280 is the 'stero chorus' model isn't it? If so, from memory, it efectovely has two separate power amps (like a Hi Fi stereo amp left and right). So the rating of EACH channel is 100W into 4 ohms or 80W into 8 ohms. So in TOTAL you'll get 200W out of the amp of 160W. You'll need to know your speaker impedance. There are two jacks per channel and the two jacks are wired in parallel. So you ciuld put, say, 2 x 8 ohm speakers in the LEFT and 2 x 8 ohm speajers in the RIGHT and that would give you 4 ohms per channel and yield 100W per channel. Or you could put jut one 8 ohm speaker in one of the LEFT sockets and another 8 ohm speaker in one of the RIGHT sockets and you'd get 2 x 80W. Does that make sense?
@@stuartukguitarampguy5830 Makes perfect sense and you wrote it so wonderfully!! Thank you!!!🏆🏆🏆
Any Opamp circuit, I check the DC on power pins AND inputs/outputs straight away. Almost everyone I've seen fail has the rail voltage at the ins/outs
Yes that's good advice.
Beautiful work sir , I still have my Marshall Valvestate VS100 laying around , abandoned it years ago after it wasn't giving any guitar output , all it does when you turn it on is crackle & pop , loud as hell , the Power Module board is 100% fine , I'm pretty sure its the preAmp , but I had "amp technicians" reject it , and I bet you would be able to easily fix it
The first thing I would do would be to clean all the pots!
Good job! I like that signal bypass thingy you used to help you diagnose the problem. Would using a surge protector help the operational amplifiers to last longer?
Hi Zak, no a surge protector would not give any additional protection to the op amps. They come from their own smoothed supply. Nice thought though! It's just an age thing, after many years some of them fail. When you think what's inside them....
Hi Stuart, an update on my 40 watt Hiwatt amp. Used your technique of poking board with a stick, looked for signal using tone generator app on my phone
Replaced 2 op amp chips and now amp is working fine. Thanks!
Any luck?
@@stuartukguitarampguy5830 Happy to report amp is working fine. I had to replace 2 op amp chips. Couldn't find exact ones but found alternatives. I'm no electronic wizard, but following your methodology worked a treat. Many thanks!
@@alastairmacintosh7149 Wow, Impressed. Well done!
That was fun to watch and informative. I have a VS100 I got in 1994 that's giving me issues. A few years ago the valve was blown but now it's intermittently working. I did notice that if I whack the top of the amp it'll come alive for a moment and then go out. I don't think it's a bad op-amp like yours was. From what you said, it sounds like dry joints might be the culprit? I'm a hobbyist with electronics so I am familiar with soldering but I really wanted to avoid removing the board. I might have a go at it. These amps are cheap now but it's got a lot of sentimental value for me plus I think it sounds nice. :)
Yes dry joints are a big problem on these amps. Quite often its the power resistors.
Having the same issue as you. Also a beginner hobbyist and have been building my own pedals (kits with ready made PCBs), so I can definitely solder/reflow cold joints. I’d have no idea where to look though... tempted to just give it to a pro, on the other hand also tempted to fix it myself...
@@jonathanonguitar The most common problem with valvestates is dry joints, particularly around power resistors. If you are interested in repairing amps etc I'd encourage you to have a go because this is exactly how you learn. All amp techs have their 'first amp' they ever worked on. It's a learning curve and the only
way is experience built one amp at a time. I've repaired thousands (literally) of amps and hardly a day goes by when I don't come across some new problem which challenges me. So it never stops! Have a go. Get started. Get a schematic and start trying to understand it. Also, there are some awesome resources out there these days. My videos, Uncle Doug, The Guitarologist etc. Experts walking you through amp after amp. Didn't exist 20 years ago. Heck you couldn't easily get schenatics 20 years ago!! Good luck!
@@stuartukguitarampguy5830 My son's amp was cutting out recently. It's a 20 year old Crate amp. I finally pulled the board after ruling everything else out. Armed with some knowledge gained here, I found a couple of cracked joints. I resoldered them and _so_ far, so good. I had retired my Marshall a while back before I could repair it. Now that I've gotten my feet wet with pulling a board out, I'll take the plunge. Great resources of knowledge here! :)
@@laserfloyd Great that's exactly why I make these vids, to help out buding amp techs!
Nice video, Stuart.
I’m forced to try this for myself, but have no knowledge of this kind of thing.
Mostly I’m abit worried about getting electricuted.
Any tips on what to stay away from?
Greetings from Denmark
Great video. Gives me hope of saving a bricked Hiwatt amp.....
Excellent. Go for it!
thanks for this video. I had a question for you. I have a Rocktek RK20R. The amp is very loud but the sound is muddy and too saturated. The tones are not clear and can't hear the characteristic sounds of my strat and tele. I plugged it into a stereo and the speaker is perfectly clear in playing radio music. All the cords are good. I think the issue is the sound processing in the pre amp part. Can circuit problems make the sound muddy and overstaturated? or is it just a poor amp. I wanted to see if it's worth going through all the circuit board looking for problems. I've played with all the setting for several hours to no avail. Thanks sir
My guess is that the amp is working as designed but you just don;t like the sound of it.
Hi Stuart. I've raelly enjoyed your videos on fixing up old Marshall Valvestate amps. I just bought an old Marshall Valvestate 8100 head that is in dire need of some maintenance (I only payed the equivalent of 50£!). I'm fairly sure it's just the pots that need a good cleaning. I am however in doubt if there are any high voltage filter caps in the amp that I have to look out for? Or are these only used in "true" valve amps with valves in the power section? I'm still very much a novice when it comes to electric circuits and the likes, but I'd love to learn how to maintain, repair, and perhaps even mod guitar amps when my knowledge and skills allow.
Hi There are HV caps in this amp but they are not very large and will quickly discharge. Ideally get the board into a position where you can see the underside. They suffer badly from dry joints particularly around the larger caps and power resistors. reflow all these. Clean the pots. Might be good to go?
Hi MrPink. Have a look at the answer blow I gave to Michael. Is it possible your FX send/return jacks (if tyhe amp has them) need a clean?
Hello Stuart, do you know where to get a transformer for the Valvestate amps? I have an 8040 from the USA which has the 120v volt PT. It seems there are no other taps on the transformer to use for 230v. Any ideas? Thank you for an interesting video.
I think I would have put a DIP8 socket in as you know who will fixing it next time...YOU...lol cheers mate great videos. Im deffo learning.
True!
Very nice video, nicely explained, all in place, cool :) Thank you
Thanks!
@@stuartukguitarampguy5830 literally since 3h I’m watching yours videos, the simplicity and engagement and honesty that you convey.. awesome!!! Surely it started as I’m having some work to do on my amp Marshall vs 8240 but I know now much more. Thank you Sir! And I know how much time it gets to document things… as a content creator I know. It would be so much easier just to make things done, but record it, explain, put it together… takes sooo much rime and additional effort. But you teach us, we appreciate it.
Thanks for the great feedback!
DUDE! WTF! YOU'RE AMAZING!
Aww shucks. Thanks Luke.
I gave my dad a Boss Katana amp that he's been very happy with, and he gave me his very poorly Valvestate S80, because I've always quite loved the Valvestate clean tones. It sounds very different than any of the famous classic tube amps, yet I don't think it sounds sterile at all. I hope some of this will help me getting it in shape. The main problem though, is that the beautiful spring reverb jumps in and out whether it's turned on or off. Any suspicion what it might be?
What do you mean 'jumps in and out'?
I have a Valvestate 8040 that I bought new in 1992. It’s had a few minor repairs including bypassing the Pre-amp jack around 10 years ago which fixed a faulty jack socket (I didn’t use this facility anyway so was easier to delete it).
I also replaced some of the scratchy pots (although cleaning them would have been easier!)
My amp was unused for 4 weeks whilst I was holiday and on return, there is almost no sound. The spring reverb works (you can hear when tapping on the tank) and when I plug into Power-amp IN, I get sound.
I replaced the 12AX7 with a new one (I assume the new one works) and no change. I’ve checked for dry solder joints and have refreshed a few joints.
There is some sound on full volume on the clean and boost channels but not close to normal. There is also a noticeable hum at high volumes.
Any advice?
I suspect an Op amp chip but I don’t have equipment to check them.
Hi It's SO difficcult to diagnose these things over the Internet. They are very prone to dry joints on the larger caps and power resistors, so maybe check that (waggling the component can cause the sound to suddenly come back). I can;t recall if this has FX send and return jaccks. If it does, clean those. Good luck!
Thanks Stuart.
There is no FX loop in this amp. I’ve been over all the solders looking for dry joints but I will specifically check the power resistors and caps.
Hi Stuart
I’m fairly certain that it’s not a dry joint. I am getting sound on the boost channel but it’s noisy (lots of hum). On the clean, there’s almost nothing except at full volume. I definitely think that it’s a component in the pre amp stage.
Can I test the op amps with a signal from my guitar similar to your technique in this video? I’m based in the Middle East so limited for options with repair. I think that I will be able to find replacement TL072s though.
@@darcycuttlefish3981 Hi Darcy Ok you've tripped my memory. I have changed MANY TL072s on these amps. It won;t be easy for you to diagnose without a scope. You could just swap out the first two chips and hope that cures it.
@@stuartukguitarampguy5830
I think that’s what I’ll do. Op amps do seem to be cheap so little to be lost. If that doesn’t work then I’ll think that I’ll get a new amp as the alternative is to transport amp back to UK to repair and that’s not worth the trouble.
Hello. I have the same model at home. I have some problems with it. The two speakers work separately if put the jackstick in from the back. I cant make the other ports work(i have only tried with jacstick from my phone, not a guitar) and if i turn the volume up and down it makes a lot of loud noices. To me it sounds like a loose connection, but i would like to get an other opinion and ofcourse know if it's worth the time and money it will take to fix it. I really hope you will answer. Regards Mark
Watching this because I have an 8080 valvestate and the normal channel volume is low and reverb does not work. Boost channel is fine. Tested reverb leads and tank, both test out ok.
Hi Hard to diagnose over the internet. 90% of time with reverb it's the tank or leads. VERY rare for it to be something else. If you have a meter you can test both sockets on the tank. Open circuit means it's bad. Low ohms means it's good. On the low volume it MAY be one of the op amp chips but honestly it's so hard to say. Good luck!
@@stuartukguitarampguy5830 Thanks for replying. Checked all that in the reverb.
Hi William. Well this one isn't easy to fix if you have NO knowledge of electronics, plus those darn 8 pin chips are a little tricky to get out.
This is probably one for an experienced amp tech. I you do have a go yourself unplug the amp leave it for an hour or so before working on it.
I often wonder, when an amp has two channels, and is rated at 100 RMS (I have a 2 channel 100 RMS Hartke GT 100), is it two discrete channels all the way through to the power stage, which would mean it’s really only 50 RMS when you plug into one or the other channel, or is it two preamps fed into one 100 RMS power amp?
Thinking back to a Sears Sivertone two channel tube amp I once had (unfortunately lost track of), that used four 6L6 power tubes. Rated at 100 watts (not sure if that’s RMS), driving six 10 inch Jensen speakers. Too late to look now, but of course I could have answered the question by looking to see if there were two audio output transformers.
I see two channels on the amp you just gave a second lease on life. Is that two preamps, fed into one power amp? Curious what is the RMS if you happen to know it as well. Thanks!
Hi. The power amp is rated at, say, 100W so the amp will give out 100W. Two channels are separate preamp channels feeding into the same power amp. Does that help?
Bottom line, 100W no matter which preamp you use.
@@stuartukguitarampguy5830 Got it! I was so used to thinking of 2 channels as stereo, left and right, from input to power output.
Though I still don’t understand why a guitar amp would have 2 separate preamp channels, feeding the same power amp, especially when you can only use one or the other, not together at the same time.
Hi. The usual reason to have 2 or even 3 completely separate preamp sections is so that you can dial in completely dfferent sounds on each and then just kick a footswitch to change between them. The most common setup is to have a 'claen' channel' and a 'drive' channel. One click and you ggo from country and western to full on metal!@@user-qm7nw7vd5s
@@stuartukguitarampguy5830 I see! So that’s what that foot-switch is for (that I kept rolled up and tucked inside the cabinet, so as not to lose ). THANKS!
Hi Stuart, I have Marshall AS80R which gives crackling noises when powered on. I have looked a the circuit boards and I found no bad solders or burnt components. What is common problem with this amps? Mine is about 15 years old and it was working until it was stored away a couple of years. Appreciate your advice at what I should to fix the problem.
Hi Jay I can;t recall if this model has FX and/return jacks. If so try cleaning those. Also turn all the controls back and forwards full range about 10x each to clean the tracks a bit. Other than that you'll need a tech. All the best.
Would you have an idea why the effects might have stopped working on my amp ? It is a Marshall AVT150X. It has multi effects - delay, chorus, flanger etc that were all going fine until yesterday. The amp itself seems ok , problem seems to be from the presence right through the effects mix, selector etc.
Hi Eric
From memory those FX are all on a little sub board inside. Might be worth checking the conections to that board.
@@stuartukguitarampguy5830 thanks Stuart, will have a look.
@@stuartukguitarampguy5830 Yeah opened it up, but really dont know what Im looking for. May have to bite the bullet and pay someone
Hi Stuart, I have a Marshall DSL20CR ( a year old), and I flipped the stand-by switch from 20 to 10 amp. while it was in play mode.Now I only get very faint sound when I try to play it. I've ordered new tubes.Do you think the tubes are the problem? Thank You.
I;m not familiar with that amp as it is quite new. When yousay 10 amp do you mean 10 watts? It's unlikely the tubes have gone after a year but since you have ordered them anyway you may as well try.
Yes I did mean Watt.There's a switch right beside the " Power " switch.' Up " is 10 watt, middle is " stand-by, and down is 20 watt.I flipped the switch from 20 to 10 while the power was on.@@stuartukguitarampguy5830
A good informative video, well done and thankyou 😁👍
Lovely channel! 👍👍
Thanks very much.
Hey Stuart, I came across your awesome video because I'm trying to fix the amp (Marshall Valvestate 40V Model 8040) my brother gave me. I made a reddit Post with a video showing what I think is wrong with this amp. Sadly my comment gets deleted when I write out the link. Is there a way I can send you the link?
Here is the text I wrote: Hey, my brother gave me his old amp, since I recently started playing guitar. He said I can try to fix it and that the gain and volume knobs are the problem. But I guess there are more problems, since the crackling sound and this periodically appearing knocking sound are always present. In the video you can hear what happens when I'm turning the volume knob of the boost channel. The volume knob doesn't work smooth at all and sometimes there is this low cut happening. The other knobs do something but this is my first amp so I don't really know what sounds to expect. Moreover, sometimes there is this reverb coming through without it being turned on.
I am an electrical engineering student and I want to learn a thing or two, since my studies are mostly theoretical.
Best Regards
Finn
Hi Finne. Yes it's annoying, TH-cam delete any comments which have a URL in them. Maybe it's to stop spam or something. If you go to the very end of any of my videos you''' see an end screen and on there is my website address, you can contact me via that. You amp seems to have a large number of different problems. The first thing I would do is remove the board and check for dry joints as these amps are VERY prone to them. In fact I've never seen one which didn;t have a load of dry joints. Stuart
@@stuartukguitarampguy5830 Thank you! I used the form on your website.
@@finne6286 ok nothing has come in yet it's stuart at chitananda dot co dot uk
My MG50DFX clean channel has very low volume, the channel switch is temperamental, do you know where to look at please? thanks in advance.
Clean all pots and switches with DeOxit D5. If that doesn;t cure it you'll need to remove the board, it will almost certainly have dry joints on it. Good luck.
I find that fitting an op-amp socket helps for the future repairs etc. And they are cheap.
Yes good idea.
Hi Stuart, I have a fender 15g frontman and the volume level is at a level 2/3 no matter how high or low you turn the knob. Whether you raise the volume knob to 10 or to 0 it stays at the same volume which I would say is about a 2/3.. the drive volume works but not the normal volume. What do you suggest?
Hi That's a really odd problem! I wonder if it's the actual volume control that needs replacing? I haven;t come across this issue before.
I wonder why I don't have that "reverb spring" in the back. I have a reverb knobs on the front. Same model but as he said different variations.
I wonder if it's been removed at some point?
@@stuartukguitarampguy5830 No - mine is on the top bolted to the amp (horizontally - yours was vertical. As you said, there were many variations of this model.)
It's always a difficult choice to repair these amps. I have an 80 watt Valvestate which cuts in an out and the cost to repair it would outweigh its value but then you have an emotional connection with these old things.
Hi Mark That will probably be a dry joint. If it was me I'd the chassis and have a gentle wiggle of some of the power resistors etc. see if you I find it. I canlt recall if this has FX sned/return jacks. If so, try cleaning those also.
Nice video, BUT.... ALWAYS.... ALWAYS pull the board out to look for cold solder joints/broken joints. I just repaired a VS232 that had no visible anomolies until I realized the input has an open connection at the input, so it took a new input jack, and good as new.
Yes these VS do get a lot of dry joints particularly around the i/p jack and the power resistors.
Please, how much watts each speaker have? I got that they are phisically same as g12t-75, but this is stock version...without numbers :)..only "g12t"....so are they 2x75 watt or?? THX
Almost certainly 75 watts per speaker.
Hi Stuart. I was just wondering if you offer any valve testing services? I have a box of old Soviet EL84s and I simply want to know which ones are ok and which ones to bin. Thanks!
Hi Yes I can do them for £1 each if you want.
@@stuartukguitarampguy5830 That sounds great Stuart, I'll take you up on that. I'll contact you via your website to arrange! Thanks.
Hi Stuart, I hope you're doing great, Do you have an advice about an amp I have, this is a Marshall Valvestate AVT20, the thing is that it doesnt bring any sound, I thought that the bulb was the problem but I just got a new one but is still mute, I noticed that the clean\od button light doesn't respond when I turn on the amp, maybe there is the problem, do you know what might be the problem with this amp? Thank You in avance :)
If the clean/od button does nothing then I suspect it's a problem with the low voltage (+/- 15V from mempry) power supply. You'll ned to find a tech to look at it.
Nice one Young Stuart! 5 *****
Cheers!
Hi Stuart, awesome work, glad you got it sorted. I have a similar problem with my VS100, turn it on, almost no sound, you hear the guitar pretty low almost inaudible. Do you have any ideas what could it be? Thank you
Hi. Always hard to diagnose such things at a distance, but if you have an FX SEND/RETURN jacks then try cleaning those with contact cleaner (just spray it in through the hole, no need to take the amp a[art) and work a jack plug in and out a few times. That is a common problem on all amps with these jacks.
@@stuartukguitarampguy5830 thx for the reply, ill try that out as soon as able. Cheers
I have the 8280 bi chorus and only can use the left output speaker but the right output is death and i dont know how to fix it 😓 both speakers are ok but i feel bad for not find a way to fix without help from a tech.
Hi. From memory the bi-chorus uses two audio amplifier power chips, one for each channel. So I expect one of those chips may have gone down in your amp. Not an easy replacement I'm afraid. The chips aren;t that expensive though.
@@stuartukguitarampguy5830 Thanks for the reply. I understand that I will not be able to do the repair on my own but I have already contacted a tech to help me repair it. I have the kinematics and I hope with that it will be easier to identify the piece to change. Greetings!
Great job!
Many thanks!
did the amp sound better after too? any tonal changes you've noticed?
Hi Svenn, no it sounded exactly the same - which is what I would expect.
Stuart, I just picked up a Valvestate 8040 40 watt with 1 x 12” Celestion. The symptoms were the same as the Valvestate in your video, power up but no sound. The previous owner said he took it to Guitar Center here in Texas, and they told him there was a problem with the board, so he bought a new amp from them. I just got the amp home, plugged it in and moved the amp, and what did I hear - loud reverb spring noise. There is no sound when I plug in the guitar into input. But when I plug the signal out from my Tascam portable guitar trainer into the preamp in, I get a strong signal, when I plug it into the guitar input I get a lower volume signal, and the sound gets louder when I increase the gain, so it’s not the jack. Do you think it could be the valve? Or would it be an op amp, What are your thoughts ?
Tricky to diagnose over the Internet. The valve is dead easy to change so start with that just to eliminate it. The power amp is working fine so it's a preamp problem. Could be an op amp 50/50. I would have thought any halfway decent amp tech could sort this for you fairly easily.
I pulled the chassis and changed the tube for a new one, no change in the symptoms. I then tried something I had read somewhere, I plugged a patch cable into the pre amp out and the other end into the power amp in, I plugged in my guitar, and to my surprise I had a nice clean and loud signal from both channels. I tried cleaning the input jacks with Deoxit and strips of paper. I ordered some replacement jacks, so next step I will remove the PCB and check the solder joints or replace the jacks.
Yes those jacks are a constant source of trouble on ALL amps whuich have that arrangement. I'm surpirsed that cleaning them didn;t do the trick though, as it sorts it in 99% of cases.
@@stuartukguitarampguy5830 i had a faulty connection on the power amp in jack, I replaced the jack, and it cured the initial problem. Now I have another issue it’s making some strange sounds with no cables plugged into it, I turn it on and turn the controls up on the clean channel and can hear what sounds like a rain shower. When I turn the boost channel on I start to hear a squeal when the gain gets close to 5 and it gets louder from there. I have attached a link to a TH-cam video: th-cam.com/video/4o3sqppYhy0/w-d-xo.html&feature=share
@@cliveblowers709 Hard to diagnose these things over the net. You have a VERY high level of gain dialled in there so you will get some hiss. It could be one of the op amps going noisy. The high-pitched squeal you are hearing is the amp going into oscillation. Sorry I can't really help more than that without seeing it.
I'm not familiar with those Integrated power amplifier SIPs. Does anyone know enough about them ? Who makes this type of IC: They certainly take some massive heat sinks, don't they
!
Hi Rich. Yes you can get them in a variety of powers from half a watt up to as
t least 100W/ Pretty god solition for a basic transistor amp.
Thanks from spainn
Hi Stuart. I am very interested in the signal generator testing method. I could also give in an audio signal out of my phone (played song, signal generator app) right? Also: what are the specs for the capacitor you´re using if you don´t mind me asking?
Hi Yes any inout signal will do to test. I think I used a 0.1uF 600V but can't remember.
@@stuartukguitarampguy5830 Thank you for your fast reply! I might have read 0.1 on the capacitor one moment in the video but it was hard to read really. Does the type of capacitor or it´s value matter too much?
@@el_micha Value not critical. You do need something with a decent voltage rating though (400V or more) as you will be sticking one end of it on various places which might have a few hundred volts floating around!
@@stuartukguitarampguy5830 Thanks again for replying quickly! Can´t be appreciated enough. Best regards from Germany
Very interesting. How do you use your phone?
I have a question if you could please help me out on this. I have a 1972 U-400G Univox 35 watt guitar amplifier that I believe has the same problem but I cannot find a replacement chip. The op amp chip number is 8022A and it seems to be not in production anymore. Do you know of a replacement number I could try? Thank you, Charlie
Hi Charles. Hmm, I see what you mean, that's quite a rare op amp and quite a fancy one from Analog Devices. I wonder why they used that chip. Is it surface mount or regular through hole? I Guess all you can do is do what I'm doing - Google searches etc. I don't have any inside info.
@@stuartukguitarampguy5830 Hi Stuart thanks for your reply. The chip is an 8 pin through hole chip. I wasn't sure if you knew of a replacement? I found some that have the same number (8022) but have a different prefix (AP8022). They are surface mount but I could make it work by soldering it to the legs (that I would leave on the board) of the old chip but was not sure if it would work or not, what do you think? Thanks again!, Charlie
@@Charles_S. Yes I found the surface mount too. The prefix doesn't matter. If you're able to solder that SM chip in
that should do the job.
@@stuartukguitarampguy5830 Thanks again Stuart, do you know of a supplier that I could buy one or two of them? I've only found suppliers that sell them in quantity (1000 + etc.). I live in the U.S. Thanks again, Charlie
@@Charles_S. Alas no, you'll just have to keep searching I'm afraid. Good luck!
The dual mono block Marshall power amps have those stupid fuses in them, never let anything foul the cooling fan as that will blow them
Ok thanks for the info.
I have a single speaker AVT 50 w valvestate. Same issue as the one in this video, I have a small dc voltage on the amp chassis when switched on. Any thoughts? Also wher do you buy the replacement op amps please?
Hi Cary EBay for the op amps. Loads of people sell them. From what reference point are you measuring the DC voltage on the chassis? Also, what is that voltage?
@@stuartukguitarampguy5830 thanks. I am getting 2 to 3 volts. I do use a multi meter at work but no expert, I was using an earth separate from the chassis and by touching the chassis with the live probe I get the reading. I may be doing something wrong?
@@gashead2 Hi Cary. Can you check with one probe on the earth of the mains plug and one on chassis and also make doubly sure you're reading volts not millivoilts. If you still get 2-3 volts you need to check the ground connectiomn from the mains lead to the chassis. I'm not 'wrried' by the 2-3V but the chassis should defo be at ground.
@@stuartukguitarampguy5830 I haven’t checked the voltage yet but I thought I would do earth continuity first. I am getting continuity between the earth on the plug and the black and red wiring on the 24v side of the transformer? Also the amp has a jack plug to connect the speaker, all of the other jack sockets show continuity to earth on one side of the jack but the speaker jack socket does not show any. I have looked at the pcb where the speaker jack is and there are no signs of distress. The amp chassis shows good earth continuity of less than 1 ohm. Any help appreciated, the amp belongs to my grandsons school and I was hoping it was dirty pots! I have tried a new valve too, thanks.
@@gashead2 Hi Cary TWo things. Forstly you won;t have any earth continuity on the speaker jack. Both contacts go to the output transformer secondary, which is not earthed, so your test on that is ok. Nothing more to do. I was unclear what you meant by the '24V side of the transformer' Do you mean a 24v AC winding? I don;t think you should be getting a reading to earth on that side of things but it's so hard to know and there's a limit to what we can do by email.
hi Stuart please could you give me some direction on checking my marshall mg 30 fx,everything lights up but no sound not even a hum -thank you
Hi John I'd love to help but it's almost impossible to diagnose something from a distance. It could be many things. Obviously check fuses and speaker connection. Sorry I can;t do more.
@@stuartukguitarampguy5830 thankyou Stuart for the reply and video,I am glad to say I have found the cause today simply the speaker was not working,should have realised this as there was no sound or hum,wish I had checked this before striping it all down,you video was very helpfull
@@johnbonada6403 Great well done.
Great video thanks
Thanks Tim.
Master laney hcm120 hardcore max no sound haw to repay
The tube is is only working the dirty channel to my knowledge ;-)