Thank you so much for this video. My Valvestate Bi Chorus 200 had been making these cracking noises for a few years. After some time of playing, usually 15-20 minutes it would stop making any sound at all. I've now cleaned all the pods with DeoxIT D5 and replaced the tube, which was really easy thanks to your clear instructions, and now my 33 year old amp sounds like new. My old Kenwood stereo amp KA-4020 also has a channel that cracks and cuts out on one channel form time to time. That's next on my to-do list.
I use an AVT (Advanced Valvestate Technology) head that belongs to my bassist… a very Marshally sounding Marshall. That tube in the preamp really gives it the warmth, punch and sag you expect from an all tube amp. And no one knows it’s a hybrid unless the get close (and know anything at all about guitar amplifiers)!
I just bought one of those for $100. The problem was the IC4 chip was supposed to be a TL074, but somebody had put in a RC4558. Replaced the chip and all is well. Just a few loose solder joints and a good pot cleaning and that thing absolutely rips!
The TL074 is a quad op amp in a 14 pin package. The 4558 is a dual op amp in an 8 pin package. How does that work? Had they put an 8-pin pack into a 14-pin space??
@@stuartukguitarampguy5830 according to the data sheet from Texas Instruments, you can get the TL074 in multiple configurations including 8 pin spider, 8 pin linear, and 14 pin ( spider or linear) its very important to be sure to order the correct one. The drawing shows the TL074 for the IC4 and the 8 pin spider tl074 is present on the board in other locations. The valvestate i have uses 3 boards: one for preamp, one for power, and a daughter for effects. I chalk it up to being British ;)
@@stuartukguitarampguy5830 you had me doubting myself because I normally work on my own amps after the kids are in bed and it's really late at night. I wasn't sure if it was a TL or TI or what, but the schematics are very clear. And the results are that I'm an idiot (but I knew that already). The chip is actually a TL072, not a TL074. I really shouldn't be trying to think after 2am :) Here is a link to the offending IC chip: www.ti.com/product/TL072 The 072 is a bi-amp and the 074 is the quad. Hence the very obvious "2" and "4" in the designator. Rookie mistake. Good thing I have a regular day job or I would surely starve to death :)
@@tjsogmc Ah that makes sense now. BUT... there's an extra mystery. The TL072 and 4558 are identical pin-outs and very similar devices. My guess is that the chip was faulty and it wouldn;t have mattered which one you put in. Those 4558s go down quite frequently.
This was my dad's go to amp for many years, and handed it done to me, it's got a few problems now, I never want to replace this amp, it's absolutely amazing
Very interesting! I am slowly bringing an unloved S80 back to life (basically works fine but some naff pots) and this video confirms that the chassis has to come out to properly clean the pots, etc. - spraying down the spindle is not very effective and the same with the jack sockets. Nice touch concerning the caps potentially being a problem for dry joints. All in all in all, a great introduction to basic maintenance and some useful pointers for those more experienced. Many thanks!
Hi Terry thanks,. Yes, definitely take the chassis out to clean the pots, also check solder connections on large capacitors and ALL the jack sockets. It should come back to life fine. Stuart
I have a ATV50 valvestate 2000 that’s drawing too much current from the transformer. I have a schematic and I have stripped the amp. I can’t see anything obvious, could you point me in the right direction please?
Love your channel Stuart! I have a 8080 that I had to fix the input jack on. I have amps I can fix now! At 64 you can end up with a few.. thank you Stuart
Great Channel Stewart! I would just like to know, who's the "person" who thought it was going to be a great idea to solder the input guitar Jack right to the motherboard!?...Let him stand up and be counted!
Just picked one of these up for $250 NZD (130 pounds)The input jack needs a re-solder…happy to tackle that now after watching this very helpful video 👌🏻 Thanks for the through content!
I have this exact problem with my Valvestate 8240. It needs a good cleaning. It was sitting around unused for over a decade. Been trying to sell it as-is but no serious takers yet. Have a feeling if I can bring it back to life, it will be easier to sell. Just need a chunk of time to do the cleaning.
@@stuartukguitarampguy5830 I'm still wrestling with that decision. Leaning toward lowering my price and seeing if anyone bites. I paid $500 for it years ago but if I can get half of that now in its current condition I suppose I should settle for that.
I just repaired a Valvestate 100 and had to put the PCB out, the input jack was broken. They use the plasic PCB spacer which are fixed with a pin from the back. Really hard to get these pins out. Why they just can not use metal PCB spacer with a screw? I also cleaned the pots like you did. These Valvestate 100 have a really bad basic hum. So I changed the caps but it had no effect. The 100 has a discret made transistor power stage. So the integraded power TDA seems much better to me. To put everything back into the cabinet, i didn't put the cabinet on its side, but on the speaker side and pushed the amp in from above. that works too.
Thank you for that knowledge. Unfortunately I can’t get the deoxit cleaner. What other brand do you recommend instead of deoxit? Or what kind of cleaner should I get? My valvestate 80 making that same noises. Thank you
Hi I'm surprised you can;t get DeOxit as it is very commonly available, even on eBay. If you can;t get it, then pretty much any switch/contact cleaner will get you out of trouble.
Hi great video Im playing through a marshall valvestate which keeps completely cutting out intermittently so i'll try cleaning the pots . A question please I have Deoxit but dont have the straw ..can you suggest a fix . Would the straw from DW40 work? Thanks
Hi from Oz :) , is it possible to upgrade the on/off switch with a toggle or red light plastic switch like the the amp on this vid? I just don't like the black plastic push button on my 80v??
Hi I have one of these and the reverb doesn't work. If you 'slap' the amps body then you can hear the springs splash through the speakers. However, the guitar signal remains dry. I also don't know how to get in to look at the tank as it is mounted inside the amplifier chassis.. how do you part the clips open? Thanks...
hi The RETURN from the tank is working ok, that's why you can hear the springs. So it's to do with the SEND. My best guess is the reverb tank is faulty. I can;t recall how to access the tank on this amp but I'm sure you'll figure it out. If you manage to get inside the tank check to see a wore hasn;t fallen off.
Doubt you'll see this comment but I'm actually suffering from the issue where when I put it in the effects loop I get no sound, the amps volume seems to fluctuate in volume nearly at random sometimes it doesn't but other times it's playable any idea on a solution?
Many great videos here. Have not had the time to look through all, but you mention in this video that you have an homemade tubetester for powertubes. Any video on that?
Hi Bjorn i haven't done a vid on that. It basically only measures bias current and I mostly use it for getting matched pairs. It's centred around a PSU I oicked off a dump! It has vriably HT and variable bias and a 6.3V output. The tested has various sockets but each with a 1ohm resistor in the cathode. I just wind up the HT to something like 350V and set the bias to give say 35mA. That's then my 'standard' against which I can check other tubes. It's a bit crude but good enough.
Great video thanks 👍🏼 I've done this procedure myself many times and it usually works... however a couple of times I've done all this, the amp has been like new. I've took it along to a practice and it suddenly packed up with a loud hiss through the speaker and a very low almost audible frazzled guitar sound (at fairly high volume) any hunch on what could cause this please?
I had that same problem years ago when i had the valvestate head. Great video as always, i know nothing about amp repairs, but i always find your videos interesting and relaxing to watch. Great work.
Sir I would like to tell you that I have been maintaining my Marshall amps for years and I just decided to fix around a bit and see if I found any new tricks or tips and I want to tell you this is probably one of the best cleaning maintenance videos I have seen the views are clear and show you what you're doing the commentary is clear and relevant not just babbling on and on and on and I truly appreciate the lack of begging for sponsorship but anyway just wanted you to know that this is without a doubt one of the best videos I have found for this particular amplifier I thank you for your time and your dedication
My first guitar amp. Really liked it. Though I am now wondering what’s the point of putting one valve in the circuit seeing the amount of op amp there is... Anyhow thank you again for some good advices.
I just dusted my S80 off today (literally). My master volume was the main problem. The issue was asymmetrical in that the right channel would crackle more and below volume 2, would cut out completely. I followed your disassembly and cleaning process for all pots and now they are all smooth and clear. My S80 is a U.S. model (8240) which may be why my reverb plate was in a different location. And of course I get a 60 cycle hum, instead of a 50 cycle. :) Thanks!
interesting. I'm looking at an amp I have, and they zip-tied the two caps together, and the zip-tie goes through a hole in the pcb around the back. So they're together, and attached to the PCB rigidly.
Hi Mark The solder comes undone on the underside of these jacks. If you can get the board to a state where you can see the soldering, just going over each one with an iron should get you out of trouble.
Hello sir! Just bought one of these, but I think mine got some issue within the boost channel. Could yout help me out with a fast test please? If you set identical Gain and EQ for both channels, and set the boost channel with max volume, does normal channel sounds louder than boost? A LOT louder like something around 50% louder. This is whats happening here.
@@stuartukguitarampguy5830 Thank you for the prompt reply. So I guess we can safely say I have a problem with my amp's boost channel? The amp just came from the assistance and guy there insists this is a completely normal behaviour for the boost channel. I don't really know what else to do. I guess i'll show him your response!
@@sarchoj Without seeing it, that's my best guess. Boost channels are nearly always significantly louder than clean channels. The clue is in the name! Good luck.
At 9:35, I can see that at least one of those caps is slightly domed and bulging on top. Probably bulging at the bottom too, which why it seems wobbly on the board....
Yes it's almost impossible to fix amps from further away than about 30 miles. Major hassle and expense to ship them safely. Many people have zero access to an amp tech in their area.
You seem to be rather knowledgeable about Marshall amps, I have a question if you don't mind, I have a Valvestate 8010 that the pots need to be replaced due to being cracked, how important are the exact values of the pots when it comes to solid-state amps? Example one pot is a 220K however with Mouser and Digikey I can only get 200K, same thing with the 22K I can only get a hold of 20K, do you think the difference in values is enough that I or anyone else would notice?
Thank you very much for this video! I recently have been given a 8240 with exactly the same issues as this one had. I hope I will get the same result after just cleaning the pots!
Hi Stuart, I'm having all sorts of humming, cracking screeching going on with my S80. The normal channel gain pot is very erratic on volume and the boost channel has a lot of buzzing. I connected the guitar to the mono left socket and everything seems ok. I've cleaned all pots several times with a contact cleaner, albeit not WD40, some pots are still tight but both gain pots seem to destabilise the amp. The reverb is a little scratchy so that will need more clean I guess the amp is early 90's but has been hardly used. I assume the valve is ok, I haven't got at tester so any advise on proving its condition would be helpful. Sorry for riding this post as such but the symtomsare very similar. Appreciate any guidance you can offer me please, Cheers, Roy
Hi Roy. Normal chennl pot is almost certainly dorty. Use DeOxit D5 on all the pots from the inside. Other than that, these suffer from dry joints so have a good look at the underside of the baord. That's the limit of what I can do over the internet. Good luck!.
Thanks Stuart, I’ve followed the protocol and the power stage seems fine. I’ve given all suspected pots another rigorous clean, the tube was heating ok and all jack sockets tapped and tested, giving it a sound test now….
Hi Stuart, some real progress, again power stage is stable, the normal channel seems ok since cleaning the gain pot thoroughly… the chorus seems good, OD1 is fine however OD2 is boosting the output but has a ‘hissing’ interference at the same time… any clues? Cheers, Roy
@@royblair5210 Good well done. The probelm with OD2 is it puts a LOT of gain in the system. You'll always get a lot more hiss/noise. But if you think it's off the scale excessive it could indicate a noisy chip. HArd to diagnose I'm afraid.
Thanks for the reply Stuart. Could it be the valve as this is easy replaced albeit ££, I could replace the chips however don’t have the test equipment really (for noise… oscilloscope rather than fluke) incidentally the red reverb unit wire was suspiciously close to touching or touching at the pcb terminals (braid and line) Not sure of relevance but parted all the same.. cheers, Roy
Excellent question! Short answer is yes, it provides one of the gain stages. Longer answer is (in my opinion) no. I believe it to be a marketing gimmick to sell a transisstor amp as a 'valve' amp as everyone wants that 'valve sound'. Again, just my opinion, but I don't think a single preamp valve can really give an amp the valve sound. But these things are VERY subjective and rarely/never tested in proper double blind conditions. I feel the same about different valve makes e.g. JJ -v- Electro Harmonix, or new -v- NOS. I believe it to be 'Emperor's New Suit of Clothes' if you know what I mean by that. I'd bet serious money that in a properly constructed double blind trial of, say, 100 guitarists comparing a NOS valve with a new valve, or a Tung Sol with a Groove Tubes that the results would be indistinguishable from random.
Hi Stuart, congratulations on your channel’s growth. Subbed a while ago. I recently plugged a Marshall Valvestate 8040v (made for American market) into 240v UK socket. It is now damaged, don’t ask! … I replaced the fuse and the normal channel made a terrible buzzing noise and the boost channel works but now has bad tone and reduced volume. I started at the tube socket (12AX7) to take some readings. Pin 1 (Plate) 248v, Pin2 (Grid) 244v, Pin4/5 (Filament) 18v??, Pin 6 (Plate) 0v, Pin 7 (Grid) 0v. I also have 3.5v AC on plates and grids. D1 and D2 are open. Only one half of the socket is receiving power? Planning to replace the diodes and Zener Diodes. There are a number of resistors out of spec, which I will address. I’d like to get the power supply operating first. I wanted to ask if you know the voltages to expect from the power transformer and auto transformer? I understand the Dagnell T593 is also used in the 8080v model. Do you have an idea why I have 18v (not 6.3v) on the filaments? Resistor 62/63 still OK. I’m assuming the AC present is due to the D1/D2 being open and possibly the rectifier block DB1 rated at 200v may have been damaged??? Do you think the opamps may have sustained damage? Any thoughts or suggestions you may have or things to look out for are very welcome. Many Thanks. drtube.com/schematics/marshall/8040-iss8.pdf
Hi. I'd check the HT caps as that might be the reason for the high AC volts. The other readings look about right. Remember you have TWO heaters in that package so if you measure across 4/5 you will get double the voltage, about 13V - AC of course. Measuring between9 and 4 or 9 and 5 should gove you 6.3V AC approx. Good luck.
@@stuartukguitarampguy5830 Thanks Stuart for your reply. I just measured between 4-5 and i'm getting 36v. I was previously was measuring between pins 4 and the chassis and 5 and chassis. It seems using pin 9 doesn't provide a reading. It may not be connected to ground. I believe I need to figure out how to read the transformer voltages on the secondary side i'm hoping I haven't damaged it with the 240v!
@@stuartukguitarampguy5830 Yes, it is 36v AC. I just replaced the valve for a few seconds to check glow and the bottom of valve is quite bright, more so than normal I would say. If i'm reading the schematic right, the filaments are powered from the power transformer, the voltage being stepped down via the 68ohm resistors. I recently changed these from 3 watts to 5 as they looked burned. They still measure 68 ohm. The schematic is not helpful in identifying the transformers wires/voltages/colours. Ummmm.
@@dembydish Hi Just checked the schematic, I've never looked at this amp before. It derives the heater voltage from the same supply which produces +/-12V DC. To do that it drops the AC down via those two power resistors. So the AC voltage measured actually at the socket (but WITH the valve in) should be about 6V on each heater. Make sure the vale is in of course, when you measure. I can't believe it's 18V AC per heater at the moment with the valve in, as that would defo burn the heater out.
Thank you for your video. The tip about the contact cleaner sprayer retrofit using a heat shrink wrap is genius. Funny how improvements always are the opposite these days. I have a question. My amp has a rf problem. I saw a person repair it by replacing imput dual op closest to the main jack. He said it is a common problem with this amp that is caused by static electricity if the guitar is plugged in while the amp is turned on. Have you ever done that repair? I unfortunately cant find the video to see which op it was and don't have the schematic. There are 2 possible candidates, one is straight in front of the jack and one is off to the side.
@@stuartukguitarampguy5830 So Stuart what do you think about the rf? I just cleaned all the pots. The overall sound is terrible, though that holds true for all my amps (nothing good) and am leaning toward all bad cords, but the rf has always been there since the day I bought it, which was why they we selling it.
Thank you so much for this video. My Valvestate Bi Chorus 200 had been making these cracking noises for a few years. After some time of playing, usually 15-20 minutes it would stop making any sound at all.
I've now cleaned all the pods with DeoxIT D5 and replaced the tube, which was really easy thanks to your clear instructions, and now my 33 year old amp sounds like new.
My old Kenwood stereo amp KA-4020 also has a channel that cracks and cuts out on one channel form time to time. That's next on my to-do list.
That's awesome well done Michel.
I would love to see Marshall reissue the original Valvestate line, just in a better quality version (sturdier, better pots and connections). ;-)
Yes that would be good.
I use an AVT (Advanced Valvestate Technology) head that belongs to my bassist… a very Marshally sounding Marshall. That tube in the preamp really gives it the warmth, punch and sag you expect from an all tube amp. And no one knows it’s a hybrid unless the get close (and know anything at all about guitar amplifiers)!
I just bought one of those for $100. The problem was the IC4 chip was supposed to be a TL074, but somebody had put in a RC4558. Replaced the chip and all is well. Just a few loose solder joints and a good pot cleaning and that thing absolutely rips!
The TL074 is a quad op amp in a 14 pin package. The 4558 is a dual op amp in an 8 pin package. How does that work? Had they put an 8-pin pack into a 14-pin space??
@@stuartukguitarampguy5830 according to the data sheet from Texas Instruments, you can get the TL074 in multiple configurations including 8 pin spider, 8 pin linear, and 14 pin ( spider or linear) its very important to be sure to order the correct one.
The drawing shows the TL074 for the IC4 and the 8 pin spider tl074 is present on the board in other locations. The valvestate i have uses 3 boards: one for preamp, one for power, and a daughter for effects. I chalk it up to being British ;)
@@tjsogmc Ok still a bit confused though. Surely the TL074 is a 4 op-amp IC? But the 4558 is a 2-op amp?
@@stuartukguitarampguy5830 you had me doubting myself because I normally work on my own amps after the kids are in bed and it's really late at night. I wasn't sure if it was a TL or TI or what, but the schematics are very clear. And the results are that I'm an idiot (but I knew that already). The chip is actually a TL072, not a TL074. I really shouldn't be trying to think after 2am :)
Here is a link to the offending IC chip:
www.ti.com/product/TL072
The 072 is a bi-amp and the 074 is the quad. Hence the very obvious "2" and "4" in the designator.
Rookie mistake. Good thing I have a regular day job or I would surely starve to death :)
@@tjsogmc Ah that makes sense now. BUT... there's an extra mystery. The TL072 and 4558 are identical pin-outs and very similar devices. My guess is that the chip was faulty and it wouldn;t have mattered which one you put in. Those 4558s go down quite frequently.
Stuart, the indent in the pot is to engage with the "stop" on the rotating part to prevent 360d rotation. (Don't ask how I know)
Aha! Thanks.
Gerbil, I am guessing you took a pot apart for cleaning and reassembled it incorrectly?! Been there myself...
@@goodun2974 Nah. From yonks ago. Wanted to see what was inside. That's how we all learn.
This was my dad's go to amp for many years, and handed it done to me, it's got a few problems now, I never want to replace this amp, it's absolutely amazing
Hi Connor they are amazingly good amps for the money.
Very interesting! I am slowly bringing an unloved S80 back to life (basically works fine but some naff pots) and this video confirms that the chassis has to come out to properly clean the pots, etc. - spraying down the spindle is not very effective and the same with the jack sockets. Nice touch concerning the caps potentially being a problem for dry joints.
All in all in all, a great introduction to basic maintenance and some useful pointers for those more experienced. Many thanks!
Hi Terry thanks,. Yes, definitely take the chassis out to clean the pots, also check solder connections on large capacitors and ALL the jack sockets. It should come back to life fine.
Stuart
Does anyone know a good source for replacement potentiometers for these guitar amplifiers?
Thank you so much for showing us your repairs and tricks!!! Cheers from Chile :)
Thanks for watching! Brazil is the closest I've been to Chile - and that's not close!
I have a ATV50 valvestate 2000 that’s drawing too much current from the transformer. I have a schematic and I have stripped the amp. I can’t see anything obvious, could you point me in the right direction please?
Sorry absolutely impossible to do without having the amp on the bench. Smoothing caps gone bad? Good luck!
Love your channel Stuart! I have a 8080 that I had to fix the input jack on. I have amps I can fix now! At 64 you can end up with a few.. thank you Stuart
Glad you like it! Well done on fixing yours.
Great Channel Stewart! I would just like to know, who's the "person" who thought it was going to be a great idea to solder the input guitar Jack right to the motherboard!?...Let him stand up and be counted!
@@dritt-drittpaniagua739 Agreed. GUARANTEED dry joints after 6 months of use.
Just picked one of these up for $250 NZD (130 pounds)The input jack needs a re-solder…happy to tackle that now after watching this very helpful video 👌🏻 Thanks for the through content!
Hi Greg Nice one. Pull the board and chack for dry joints all over, you'll find plenty!
I have this exact problem with my Valvestate 8240. It needs a good cleaning. It was sitting around unused for over a decade. Been trying to sell it as-is but no serious takers yet. Have a feeling if I can bring it back to life, it will be easier to sell. Just need a chunk of time to do the cleaning.
I suppose it depends how critical money is. They are not valuable amps and you'd maybe get £75 more or something if it was working.
@@stuartukguitarampguy5830
I'm still wrestling with that decision. Leaning toward lowering my price and seeing if anyone bites. I paid $500 for it years ago but if I can get half of that now in its current condition I suppose I should settle for that.
Nice one Young Stuart!
Thank you!
Thank you Stuart.This tutorial worked for me.From silent to sound.
I'm pleased you enjoyed it.
I just repaired a Valvestate 100 and had to put the PCB out, the input jack was broken. They use the plasic PCB spacer which are fixed with a pin from the back. Really hard to get these pins out. Why they just can not use metal PCB spacer with a screw?
I also cleaned the pots like you did.
These Valvestate 100 have a really bad basic hum. So I changed the caps but it had no effect. The 100 has a discret made transistor power stage. So the integraded power TDA seems much better to me.
To put everything back into the cabinet, i didn't put the cabinet on its side, but on the speaker side and pushed the amp in from above. that works too.
NIce one Well done.
Thank you for that knowledge. Unfortunately I can’t get the deoxit cleaner. What other brand do you recommend instead of deoxit? Or what kind of cleaner should I get?
My valvestate 80 making that same noises.
Thank you
Hi I'm surprised you can;t get DeOxit as it is very commonly available, even on eBay. If you can;t get it, then pretty much any switch/contact cleaner will get you out of trouble.
Hi great video
Im playing through a marshall valvestate which keeps completely cutting out intermittently so i'll try cleaning the pots .
A question please I have Deoxit but dont have the straw ..can you suggest a fix .
Would the straw from DW40 work?
Thanks
Hi Julian. Have a play to see if you can get a straw to fit somhow. If not you could buy yourself a new can and use the straw for both?
Hi from Oz :) , is it possible to upgrade the on/off switch with a toggle or red light plastic switch like the the amp on this vid? I just don't like the black plastic push button on my 80v??
Yes that could defintely be done by a tech.
Bought this Amp new in the early to mid 90's, worst Amp I ever owned. Nothing but problems.
Yes all these valvestates are pretty poor build quality with lots of problems.
Great tutorial! My Marshall Valvestate 8080 came back to life again.
Awesome. Well done Rodrigo!
You’ve got to clean your pot .
thank you for this.. i hope someday i will be as good as you on repairing..
I'm sure you will. It's just a matter of 'hours served'!
I always thought that the dent on the pot was the stop in either direction !
Yes you're right! Just found that out myself.
Thank you amigo !
The best video showing how to maintenance our marshall, easy and right to the point. thank's a lot mister cheers from italy
Thanks Fabian
Glad to see a new video from you Stuart. I don't know why I enjoy seeing all these amps, inside and out. But keep em coming
I will!
Hi I have one of these and the reverb doesn't work. If you 'slap' the amps body then you can hear the springs splash through the speakers. However, the guitar signal remains dry. I also don't know how to get in to look at the tank as it is mounted inside the amplifier chassis.. how do you part the clips open? Thanks...
hi The RETURN from the tank is working ok, that's why you can hear the springs. So it's to do with the SEND. My best guess is the reverb tank is faulty. I can;t recall how to access the tank on this amp but I'm sure you'll figure it out. If you manage to get inside the tank check to see a wore hasn;t fallen off.
@@stuartukguitarampguy5830 thank you
Doubt you'll see this comment but I'm actually suffering from the issue where when I put it in the effects loop I get no sound, the amps volume seems to fluctuate in volume nearly at random sometimes it doesn't but other times it's playable any idea on a solution?
Have you tried just putting a jack-jack lead in the FX loop?
@@stuartukguitarampguy5830 got a siren like sound putting a cable into input and send. Got nothing from send and return
Sorted my issue. Thanks a lot.
Excellent well done
Stuart
Many great videos here. Have not had the time to look through all, but you mention in this video that you have an homemade tubetester for powertubes. Any video on that?
Hi Bjorn
i haven't done a vid on that. It basically only measures bias current and I mostly use it for getting matched pairs. It's centred around a PSU I oicked off a dump! It has vriably HT and variable bias and a 6.3V output. The tested has various sockets but each with a 1ohm resistor in the cathode. I just wind up the HT to something like 350V and set the bias to give say 35mA. That's then my 'standard' against which I can check other tubes. It's a bit crude but good enough.
Thank you for taking the time to answer.
@@stuartukguitarampguy5830
Great video thanks 👍🏼 I've done this procedure myself many times and it usually works... however a couple of times I've done all this, the amp has been like new. I've took it along to a practice and it suddenly packed up with a loud hiss through the speaker and a very low almost audible frazzled guitar sound (at fairly high volume) any hunch on what could cause this please?
Hi Tim. Tbh that could be almost anything e.g. an intermittne dry joint. You;d need to fault-find it when in the 'faulty' condition.
I had that same problem years ago when i had the valvestate head. Great video as always, i know nothing about amp repairs, but i always find your videos interesting and relaxing to watch. Great work.
Thanks Mark!
It’s not a dirty pot, it’s a home made tremelo 😂 It’s not a problem, it’s a feature! 😝
Sir I would like to tell you that I have been maintaining my Marshall amps for years and I just decided to fix around a bit and see if I found any new tricks or tips and I want to tell you this is probably one of the best cleaning maintenance videos I have seen the views are clear and show you what you're doing the commentary is clear and relevant not just babbling on and on and on and I truly appreciate the lack of begging for sponsorship but anyway just wanted you to know that this is without a doubt one of the best videos I have found for this particular amplifier I thank you for your time and your dedication
Thanks Timothy. Yes it's an irksome feature of modern life that everyone is trying to monetise everything.
My first guitar amp. Really liked it. Though I am now wondering what’s the point of putting one valve in the circuit seeing the amount of op amp there is...
Anyhow thank you again for some good advices.
That's easy to answer! Marketing!
I just dusted my S80 off today (literally). My master volume was the main problem. The issue was asymmetrical in that the right channel would crackle more and below volume 2, would cut out completely. I followed your disassembly and cleaning process for all pots and now they are all smooth and clear. My S80 is a U.S. model (8240) which may be why my reverb plate was in a different location. And of course I get a 60 cycle hum, instead of a 50 cycle. :) Thanks!
Hi John Well done for gtting it sorted! For some reason the pots on these amps do not like to be left unused for any period of time.
interesting. I'm looking at an amp I have, and they zip-tied the two caps together, and the zip-tie goes through a hole in the pcb around the back. So they're together, and attached to the PCB rigidly.
Aha I'm wondering if that was factory done or if someone has been in there.
I have the same amp and the sound is intermittent if l wiggle the input jack or force it down it works. Do l need a new jack socket ?
Hi Mark The solder comes undone on the underside of these jacks. If you can get the board to a state where you can see the soldering, just going over each one with an iron should get you out of trouble.
Amazing job! A new amp... 👏🏼👏🏼👏🏼
Tell me: in UK, are possible buy the faceplate of VS100?
Thanks Arnor. I would just Google that and see if anyone is offering it. Stuart
Hello from Brazil! Excellent video!!
Thank you Sir. Excellent video. Super helpful, very precise.
Thanks Alex
Hello sir! Just bought one of these, but I think mine got some issue within the boost channel. Could yout help me out with a fast test please? If you set identical Gain and EQ for both channels, and set the boost channel with max volume, does normal channel sounds louder than boost? A LOT louder like something around 50% louder. This is whats happening here.
Under those conditions I'd expect the BOOST channel to sound a LOT louder than the clean channel.
@@stuartukguitarampguy5830 Thank you for the prompt reply. So I guess we can safely say I have a problem with my amp's boost channel? The amp just came from the assistance and guy there insists this is a completely normal behaviour for the boost channel. I don't really know what else to do. I guess i'll show him your response!
@@sarchoj Without seeing it, that's my best guess. Boost channels are nearly always significantly louder than clean channels. The clue is in the name! Good luck.
You indeed have great principals Stuart. I would be so happy to be your apprentice!
Thanks Otto!
At 9:35, I can see that at least one of those caps is slightly domed and bulging on top. Probably bulging at the bottom too, which why it seems wobbly on the board....
Nah, they were fine.
Excellent video and very informative, I wish I lived closer so you could service my Marshall 8240👍
Yes it's almost impossible to fix amps from further away than about 30 miles. Major hassle and expense to ship them safely. Many people have zero access to an amp tech in their area.
You seem to be rather knowledgeable about Marshall amps, I have a question if you don't mind, I have a Valvestate 8010 that the pots need to be replaced due to being cracked, how important are the exact values of the pots when it comes to solid-state amps? Example one pot is a 220K however with Mouser and Digikey I can only get 200K, same thing with the 22K I can only get a hold of 20K, do you think the difference in values is enough that I or anyone else would notice?
Hi, those substitue values will be fine.
@@stuartukguitarampguy5830 Thank you very much for the info, Cheers
Thank you very much for this video! I recently have been given a 8240 with exactly the same issues as this one had. I hope I will get the same result after just cleaning the pots!
Let's hope so. They are also very prone to dry joints so ideallt take the board out and have a careful look with an eye glass.
Your channel is amazing!!! Thank you so mutch for the entertaining and educational content! Keep up the amazing work!
Thanks very much.
Hi Stuart, I'm having all sorts of humming, cracking screeching going on with my S80. The normal channel gain pot is very erratic on volume and the boost channel has a lot of buzzing. I connected the guitar to the mono left socket and everything seems ok. I've cleaned all pots several times with a contact cleaner, albeit not WD40, some pots are still tight but both gain pots seem to destabilise the amp. The reverb is a little scratchy so that will need more clean I guess the amp is early 90's but has been hardly used. I assume the valve is ok, I haven't got at tester so any advise on proving its condition would be helpful. Sorry for riding this post as such but the symtomsare very similar. Appreciate any guidance you can offer me please, Cheers, Roy
Hi Roy. Normal chennl pot is almost certainly dorty. Use DeOxit D5 on all the pots from the inside. Other than that, these suffer from dry joints so have a good look at the underside of the baord. That's the limit of what I can do over the internet. Good luck!.
Thanks Stuart, I’ve followed the protocol and the power stage seems fine. I’ve given all suspected pots another rigorous clean, the tube was heating ok and all jack sockets tapped and tested, giving it a sound test now….
Hi Stuart, some real progress, again power stage is stable, the normal channel seems ok since cleaning the gain pot thoroughly… the chorus seems good, OD1 is fine however OD2 is boosting the output but has a ‘hissing’ interference at the same time… any clues?
Cheers, Roy
@@royblair5210 Good well done. The probelm with OD2 is it puts a LOT of gain in the system. You'll always get a lot more hiss/noise. But if you think it's off the scale excessive it could indicate a noisy chip. HArd to diagnose I'm afraid.
Thanks for the reply Stuart.
Could it be the valve as this is easy replaced albeit ££, I could replace the chips however don’t have the test equipment really (for noise… oscilloscope rather than fluke) incidentally the red reverb unit wire was suspiciously close to touching or touching at the pcb terminals (braid and line)
Not sure of relevance but parted all the same.. cheers, Roy
Stuart, does the valve actually do anything useful in this amp?
Excellent question! Short answer is yes, it provides one of the gain stages. Longer answer is (in my opinion) no. I believe it to be a marketing gimmick to sell a transisstor amp as a 'valve' amp as everyone wants that 'valve sound'. Again, just my opinion, but I don't think a single preamp valve can really give an amp the valve sound. But these things are VERY subjective and rarely/never tested in proper double blind conditions. I feel the same about different valve makes e.g. JJ -v- Electro Harmonix, or new -v- NOS. I believe it to be 'Emperor's New Suit of Clothes' if you know what I mean by that. I'd bet serious money that in a properly constructed double blind trial of, say, 100 guitarists comparing a NOS valve with a new valve, or a Tung Sol with a Groove Tubes that the results would be indistinguishable from random.
I've watched many of your video's, and I must say you are very thorough with the repairs. Thanks for doing them. Cheers
Thanks Ken!
Hi Stuart, congratulations on your channel’s growth. Subbed a while ago. I recently plugged a Marshall Valvestate 8040v (made for American market) into 240v UK socket. It is now damaged, don’t ask! … I replaced the fuse and the normal channel made a terrible buzzing noise and the boost channel works but now has bad tone and reduced volume.
I started at the tube socket (12AX7) to take some readings. Pin 1 (Plate) 248v, Pin2 (Grid) 244v, Pin4/5 (Filament) 18v??, Pin 6 (Plate) 0v, Pin 7 (Grid) 0v. I also have 3.5v AC on plates and grids. D1 and D2 are open. Only one half of the socket is receiving power? Planning to replace the diodes and Zener Diodes. There are a number of resistors out of spec, which I will address. I’d like to get the power supply operating first. I wanted to ask if you know the voltages to expect from the power transformer and auto transformer? I understand the Dagnell T593 is also used in the 8080v model.
Do you have an idea why I have 18v (not 6.3v) on the filaments? Resistor 62/63 still OK.
I’m assuming the AC present is due to the D1/D2 being open and possibly the rectifier block DB1 rated at 200v may have been damaged??? Do you think the opamps may have sustained damage?
Any thoughts or suggestions you may have or things to look out for are very welcome. Many Thanks.
drtube.com/schematics/marshall/8040-iss8.pdf
Hi. I'd check the HT caps as that might be the reason for the high AC volts. The other readings look about right. Remember you have TWO heaters in that package so if you measure across 4/5 you will get double the voltage, about 13V - AC of course. Measuring between9 and 4 or 9 and 5 should gove you 6.3V AC approx. Good luck.
@@stuartukguitarampguy5830 Thanks Stuart for your reply. I just measured between 4-5 and i'm getting 36v. I was previously was measuring between pins 4 and the chassis and 5 and chassis. It seems using pin 9 doesn't provide a reading. It may not be connected to ground. I believe I need to figure out how to read the transformer voltages on the secondary side i'm hoping I haven't damaged it with the 240v!
Hmm that's very strange. AC, right? If it WAS 36V then the preamp valve would glow REALLY brightly and probably burn out. What's it's 'glow status'?
@@stuartukguitarampguy5830 Yes, it is 36v AC. I just replaced the valve for a few seconds to check glow and the bottom of valve is quite bright, more so than normal I would say. If i'm reading the schematic right, the filaments are powered from the power transformer, the voltage being stepped down via the 68ohm resistors. I recently changed these from 3 watts to 5 as they looked burned. They still measure 68 ohm. The schematic is not helpful in identifying the transformers wires/voltages/colours. Ummmm.
@@dembydish Hi Just checked the schematic, I've never looked at this amp before. It derives the heater voltage from the same supply which produces +/-12V DC. To do that it drops the AC down via those two power resistors. So the AC voltage measured actually at the socket (but WITH the valve in) should be about 6V on each heater. Make sure the vale is in of course, when you measure. I can't believe it's 18V AC per heater at the moment with the valve in, as that would defo burn the heater out.
Such a lovely video.
Thank you for your video. The tip about the contact cleaner sprayer retrofit using a heat shrink wrap is genius. Funny how improvements always are the opposite these days.
I have a question. My amp has a rf problem. I saw a person repair it by replacing imput dual op closest to the main jack. He said it is a common problem with this amp that is caused by static electricity if the guitar is plugged in while the amp is turned on. Have you ever done that repair? I unfortunately cant find the video to see which op it was and don't have the schematic. There are 2 possible candidates, one is straight in front of the jack and one is off to the side.
Hi Leslie
No thats an absolutely new one on me, nver heard of it.
@@stuartukguitarampguy5830 So Stuart what do you think about the rf? I just cleaned all the pots. The overall sound is terrible, though that holds true for all my amps (nothing good) and am leaning toward all bad cords, but the rf has always been there since the day I bought it, which was why they we selling it.
@@lesliel1182 Hi Leslie, Sorry I can;t come up with a simple solution on that one.
A genuine artist at work. Cheers 🍻
Thanks Mick!
Thank very much from Canada , you lesson was very instructive. I learned a lot from it .
Excellent that's why I do the vids. All the best. -5C here but you wouldn't know anything about such cold temperatures I expect....
@@stuartukguitarampguy5830 I'm from Canada ! we will get -25 in january . Regards
@@mce377 Yes I expect you guessed that was my attempt at humour! All the best
@@stuartukguitarampguy5830 Yes sir i did , thank you very much again.
Thank you sir! You are a gem!
Ta Guv!
Great job
Thanks!