I would like to point out that the number 10 is considered unluck by the chinese. Something about the characters that make up the number 10 mean "bad luck" or some such.
Marshall has been using 'cardboard' for their cabinet back panels since the 70s. I'm sure it was a cost savings move, but MDF also has desirable sonic qualities (lack of reflection) as a back panel. Also, like most amps, it's wrapped in tolex and therefore quite unlikely to fall apart. At the least, "you get what you pay for" logic certainly does not apply to this example, as 1960 cabs are not inexpensive. Not to mention, for many years, these 'cardboard' cabs were made in England. Many MIC products (e.g., the Squier Classic Vibe series) will stand toe to toe with their more expensive, made elsewhere, equivalents these days. Many of them are rebadged products from other, american and European companies (the result of our sending our labor overseas for cost savings). Just sayin', the well worn absolutes are far from absolute...
The circuit, tubes and transformers that make of the amp are not bad at all. The real limiting factor is the 8-in speaker which makes it overall 'tinny' sounding. You can actually manage to fit a 10-in Alnico speaker in there and it clears the tubes and transformers. popular are the Jensen P10 and Eminence 1028k. You do have to dremel a bit of the bottom of chassis and make a new speaker baffle, but this is an easy hour-long project on the weekend. Really wakes the amp up and it's still beautifully compact
The speaker used judging by the basket stamping is a Rola USA alnico . By 5his time Rola UK had bought Celestion and used large cylindrical alnico magnets.
Brad, I really like your channel and took away a real nugget from this Valve Junior mod video. As you reviewed all your mods, the one that didn't get any "air time" was the Zobel network across the output transformer. I design low-watt but high gain single-ended amps w/o global feedback. I can tame oscillations just fine but that "fizz" remains. The "ah-ha" moment was seeing you add the Zobel. I immediately clipped in 10R/50nF across the speaker and the results are amazing. Many thanks for the tip.
"disregard the noise, but let's listen to the tone... KSDHFHAWIUFEACKDJFA how about that for tone?" hahahahaha I think I woke up the whole house laughing. made my day. I love your channel, man. I've watched a bunch of your videos and I just want to build an amp now, you're doing a great job at demystifying this trade, your playing is fantastic, your commentaries are insightful and your love for tinkering is contagious. Cheers!
I'm an amp tech also and I really like your videos you are very practical and use common sense and logic. I have been repairing electronic equipment all my life and I am not to vane to admit I learn from you . thanks for the great videos.
absoloutly go to the eminence factory please!!! love watching what you do. I would also like to see a scrapper amp build or builds using parts from various common "junk" equipment. instead of converting, rather using salvaged parts to create something completely different.
I think it could be hilarious if you toured the plant and told them all about how the factory in China, you know the real one, does things. You could just make up a bunch of crap about them, what are they going to do after all? Just think of all the cost saving advice you could offer, lol.
Love these things, got the head version. Only did one mod so far to boost the volume. And added two 4ohm speakers for portability without added cab. Great stuff. Good comments. Awesome results as usual Brad. Thank you again
You are correct on the resistor. I'm going to make another video testing discharge times with and without it in place. But the cap... It's on the power side of the plate resistor. I see there's an RC network set up by the plate resistor and that cap, but the fact that it's in parallel with a much large power cap makes it seem a bit pointless. Usually when you see those, you see an extra dropping resistor separating it from the larger power cap on the rail.
The 22uF/220R/22uF circuit is a CRC filter to reduce hum cheaply, instead of using a choke. You could use 47uF/100R/47uF for better filtering and less sag. The 220k resistor is a SAFETY MEASURE, it's used to discharge the B+ caps, PLEASE put it back!!!
Absolutely, there is nothing to discharge those capacitors without that resistor aside from the very low leakage current. If you think it's going to affect tone, you can put in a bigger one so the caps discharge more slowly, but don't take it out.
Thanks for the comment! You are correct. My brain was farting out at 3AM again, got tunnel vision visualizing a typical Champ power supply. Vintage amps don't typically have drain resistors. The conduction of the tubes as the amp powers down usually takes care of smaller value caps like this, no problem. In fact, I should make another short video of the cap discharge rate with and without the resistor in place. Should be informative. My hunch is, it's a measure designed to clear regulations rather than actually discharge these caps, but I could be wrong.
If something happens to the tubes, like, the filament opens, or some other damage that stops them from conducting current, or you test the circuit without the tubes in, there's always a risk of shock right after turning everything off. The resistor is a very simple and effective safety measure to greatly reduce that risk of shock, and it only uses a few miliwatts off the B+. Always better to have a resistor discharge a capacitor rather than yourself doing that job.
I bought an Epiphone Valve Jr and after modding it a bit I had the same issue that it sounded to fizzely for my taste. After asking a fellow amp tech we changed the R15 resistor from 1.5k to 100k Ohm. His reasoning was that the pre-amp creates too much amplification for the grid of the EL84 and by increasing R15 it could become smoother over all. We've tried it and it was instantly better. Additionally we added a "Bone Ray / Roy Bean" tone stack after the volume put which made this amp super easy to dial in now. There is a book "Designing Valve Preamps for Guitar and Bass" by Merlin Blencowe which had the schematic - I couldn't find the schematic on the web. Essentially its a Tilt and Middle control which is quite effective and offers quite a variety of sounds. Also I hook it up to an Eminence Cannabis Rex 12" speaker and it sounds wicket cool - or at at least a lot better than before :)
If anyone is wondering about the purpose of some of the removed components. The resistor to ground in the power supply was there to slowly discharge the high voltage after the amp is turned off, it is a safety feature. The small capacitor in the power supply that is in parallel with a much larger one is there to handle high frequency ripple since the large cap has a high inductance. I would have left those two parts in place.
I can't imagine seeing a resistor in an amp that has seen enough current to scorch it and think "I'll just remove it and add a jumper. That will be fine." 🤣
Your videos are very inspiring. I built my own amp from a kit about a year ago and after making a few tweaks and mods, I've realized I like messing around with a circuit even more than I like playing guitar. Just ordered my second amp kit and looking forward to that experience again.
Awesome job Brad! I loved your attitude going into this. For what it's worth, I think it sound pretty good at the end. My first amp ever was a 15 watt solid state Fender amp with an 8" speaker. Since then, I've pretty much always preferred amps with 12" speakers and I suspect that this amp would sound pretty good through an open back cab with a low wattage, vintage voiced 12" speaker (or a pair of them). I'll check out the follow up video too.
That's what I was thinking also. The speaker is definitely the worst part of the combo in its original state. My first amp was a similarly cheap tube amp combo with a cheap 10" and as soon as I hooked it up to a quality 12" speaker I stopped being as concerned about getting a new amp. It was a whole new world of tones.
Re. speakers for these, I put a 'Celestion Eight 15' in mine, which is a good improvement over stock. Brad, with me being a guitarist/amateur guitar tech the stuff you do with amps is firmly in the realm of 'give it to someone else to fix', for me. But fascinating to watch and strangely addictive. Thanks for posting, keep it up.
Modified versions of this amplifier can sound fantastic, the modifications to the power supply though in particular are random and ill conceived. You bypassed a resistor that is a section of an RC filter, you also removed a bleed resistor not even knowing why it was there. The 0.1uF capacitor across the 22uF is a common approach to mitigate self resonance that aluminium electrolytics are known for, it is not a great engineering solution. Randomly removing the capacitor likely had no effect at all.
The high value resistor that was removed from the power supply (where it was in parallel with the caps) was a safety feature, meant to drain charge off of the caps after the amp is turned off.
I've gone through most of your videos once and am going back over many for a second and even 3rd time or more, al a fantastic bandmaster to JTM conversion. Just ignore the occasional A hole and keep doing this. We love you dood...
Osmosis is a good way to learn. But don't always take my word for it. As others pointed out in the comments, I don't always know what I'm talking about either. Brain farted on the power supply on this one.
Great channel ! Especially the dumpster finds. More bass gear please. I don't understand the the electronics but I know what my ear tells me. The little Epiphany amp sounded awesome after your mods. Cudos
A 10 inch speaker would solve the fizzy tone I think. Great job for only a few parts. Your idea about a small Pico cap to ground or screen to plate works. I did this on an Orange Dark terror. Even across the plate resistors which I dont normally like to do, add a 100pf or 200pf there and trim off those fizzy overtones.
I used to have the head version of this, and I ran it through a Marshall 1960B 4x12 with 4 75 watt celestion GTs, it sounded amazing when you cranked it all the way. I don't know anything about messing with circuits like this, but i really want to learn. Love your videos. It seems like a super-valuable and handy skill to be able to modify electronic circuits instead of having to be at the mercy of manufacturers like the general public. Thanks for making these videos. It was super interesting to see how the tone shifted based on the capacitor and resistor changes you made. I'm learning a lot...
The harsh buzzy overtones when it's dimed out, ugh. I have best luck with humbuckers on this amp, neighborhood of 5, cleanish rhythm sounds. Single coils, I gotta run it through eq or the bottom end disappears. Bought mine in 05 or 06, I think it's the first version of the circuit. I've run the speaker in the cab on a very similar low powered Hughes and Kettner tube head from the early 90s, and I'll tell you, the speaker and cab aren't what's lacking. I'm in the middle of your vid as I write this but I think your mods are on the right track. I know nothing and play even less, but thumbs up.
Sounds great! A buddy of mine totally redid my Junior 10 years ago, hand wired on a new board...and it sounds very Vox-y. I run mine through a 1x12 loaded with an EV speaker. It just kills. Great vid, as usual!
Wow! I just started watching your vid on an amp mod,then I hear you demonstrating its tone prior to mod.your guitar skills are top shelf;the speed and fluidity you possess floored me,especially when I saw you only run with three fingers.Bravo!Keep it coming,please.
You are right. It's part of the filtering network. I only mentioned the voltage drop because I'd already decided to eliminate it and figured it wouldn't affect the voltage at the OT node much at all.
Volume control seems to be an unnecessary luxury option. Most of us probably have a volume knob in the guitar. 😀 Old alnico speakers, if they are in good condition, are sometimes real gems. I have a late 50's very elliptic shaped Rola alnico speaker which sounds just unbelievably good. And with these two tube amps, if you want different, more relaxed clean tone, try 12AT7/ECC81. I just recently tried a brand new JJ ECC81 instead of 12AX7 in one of my amps and it sounds absolutely great when playing at clean volume.
I had this amp when it was new. Owned it for a looong time as my only amp, with just some pedals. Remember saving cash for this to replace my first amp which was a little 15 watt ss crate. Thanks for posting this video! Now I wish I've still had this thing.
So this amp goes to 11? You know when you need that little extra it goes to C 11. Amazing looking build from the factory. Love your videos. I can even sing let alone play a instrument.
Gotta love Pyotr Belov's amp designs. I've got a custom one-off build he did, and have owned a number of his designs (Epiphone VJ, SoCal, Blackheart Little Giant, etc.) and have always thought the quality was far beyond the price point. That, and as a mad scientist, he builds most of his designs to be modded.
Just wanted to say that I successfully installed an Eminence 1028k speaker in one of these. some dremeling and new speaker baffle was made with the original grill cloth stapled onto it, but it totally worked. in conjunction I made all of the resistor changes in this vid, opted for Mojotone Dijon capacitors of same stock value. They really tame a lot of the brittleness inherit in this amp. 150pf ceramic 'bright cap' on the left and center lug of the volume control to "open it up" a little bit at lower volumes. It's so perfect as is now, I'm afraid to modify it any further.
The first cap/resistor/cap arrangement straight out of the rectifier is called a PI Filter. It’s there to lower the ripple (hum) on the power supply. I prefer replacing the resistor with a choke as you get less sag, and a better filter to clean up the power supply noise. The 0.1uF cap on the power supply is there because big electrolytic caps have poor HF performance. The 220k to ground is so your power supply can safely discharge when the amp is off.
r11 is to drain the voltage when the amp is powered off. r10 in combination with c9 forms an RC filter for less hum. Edit: C11 is for high-frequency bypass, where C8 is for lower frequency bypass
the speakers on guitar amplifiers attributes a massive amount to the tone of your guitar amplifier. Johan Segeborn has some great videos on the subject and everything marshall, Mr Wampler(yes the guy who makes awesome pedals) also demos 10 amplifiers through one cabinet to show how much several different amps sound very similar when using the same speaker.
The CE marking means "European Conformity", basically the same as an FCC marking here in the USA. Only thing is with the PRC which has humorously decided to use a near identical marking for "China Export", which is officially an unofficial marking so the EU can stick it.
Hello from Washington State.....and thank you for the video. I was forced to open my Epi valve Jr. (head) as I left it on overnight to a failed condition. And...now need a schematic....found by your hand to what I now study for repair end goal. I use the unit as source by fender frontman to Fender Cab. And, I really like the warm tone. Just a bit of hum...but I find the crunch input is remarkable at higher volumes and what I enjoy from a Jackson set of pickups. And, at unit open, first test run...did not find the failure. So I am studying the values to continuing test and intended replacement. With no hurry, routine repair (and or replacement). I might be that person looking over you shoulder....and liking the clear presentation of mods...best avenue to improved performance as I am working to repair+ end damaged finding. I like the absolute best value as job process and reliable use.
just watched your video, it was fun. I actually just gutted a valve junior to make a small trainwreck with the chassis. It was a very good lesson for people starting out. You explained everything you did very well step by step for your audience. At the end of the video you layed out all your changes and you added the fact of a zobel network , but you never went over that in your video, some of them might not know what it is or why you did it. Good job and keep on building.
Boy you get a lot of comments fast, don't you. Nice video, Brad. A Valve Jr. was my first build (built it in a computer power supply as the chassis). I've hardly used it since I built it. Just not a great sounding amp. I like what you've done with this one, though. I might do a rebuild of it... That speaker at about 30:35 is Best brand (EIA code 371).
I have an Epi Valve Jr Head plugged into a speaker that came from a late 1970s Fender Twin Reverb that is mounted in a Pine Cabinet that my wife built. At full volume it is loud. It is full. It is not fizzy. It is hard rock and roll. And in my small music room it is very easy to control the feedback and sustain endlessly. When I have it set to about 9 and run my guitar in stereo thru an analog chorus with my Dual Showman it sounds as pure and clean as any stereo. I am looking to buy a few of these and replace the electronics with some fiberboard mounted components just for grins.. Sort of trying to teach myself the dying art before I croak! Thanks for posting your videos, I glean a lot from them.
The 220k 2/3W to earth is a power cap drain resistor and is common in many amps but usually sits before the first cap stage . The use of one cap with no power node is purely for filtering and is very common . The resistor between the 2 will be a wirewound and will act like a choke not drop any voltage . This is left over from the days when small amps had a 1k 25W choke driving the speaker straight from the first cap , like the Valcos ( Oahus) and Gretschs 6155s etc of the 50s . Kind of like the standby switch , totally unecessary but traditional. 1 22 uf filter and 3 x 22uf caps are plenty for this amp and more than the original Vox AC4 with a 12ax7 trem tube . The weird one on the end of the chain is a mystery unless a solid state LDR type trem version was planned as small value electrolytic caps are often found in those trem circuits . The speaker is a Rola alnico going by the basket stamping . Rola UK used the same baskets but large cylindrical alnico magnets and by the 50s had bought Celestion who produced them at Thames Ditton or in London before moving to Ipswich . The 10" ribbed cone variety works great in pairs , but are very nice as singles too .
I have owned the Epiphone Valve Junior 5 watt combo with the 1x12 cab and I loved it. One of my biggest hurdles of practicing is my constant tweaking and fiddling with the knobs to try and get that "perfect" tone. With pedals, amp and guitar, just too many things to try and tweak. This eliminates a third or those temptations. My guitar has a single humbucker with one volume knob. There's another third gone. Simple and sweet. With a Gibson SG and a Mesa Boogie Mark V, I am paralyzed with options!
Not saying this applies to you at all, but I used to manage a music store and one of the most eye-opening things for me to witness was the sheer number of people who were, to put it kindly, very BAD at guitar, yet who would come in to test drive a Mark V or Road King II or something, thinking that a better amp would make them better players. Nothing wrong with wanting good tone as a starting point for improvement, but it seemed more like they were looking for some shortcut to avoid 10,000 hours of practice.
lol I know you were being sarcastic, but what you said is very true. Many guitarist (me included) think that new amp of pedal will fix our shortcomings, so we spend truck loads of cash like it will be the magic fix. Well, it don't quite work that way. And not just jamming along side a backing track (like I do)
I used to have the mini stack. It was all ply and looked great. It was a bit quiet and a bit dark (I used to use it with a homemade rangemaster). I had to source and fit a replacement output transformer after it died mid practice. I liked how it had a 'proper' pot after the nightmare blues junior pots. I now have a Laney cub10, it's just beautiful sounding, and LOUD!
I just got into your channel and love it. I just bought the Epiphone Valve Jr Head it came with a Sunn Tranducer 1216G speaker versus the Eminance stock speaker should I be concerned or is that an upgrade. I think that amp has been modified it certainly has been opened.
I just bought the head version of these with some nicer tubes and a late 90s fender 1x12 cab. If I'm honest I'm blown away by just how loud it is and how good it sounds. I originally bought it as a toy to mod by my opinion has been changed and it will become a rehearsal amp for sure. I hate to rant but I'm excited haha. I'm also surprised at how incomparable the tone of the TH-cam reviews I've seen is to my amp.
As for dating this amp, the serial # may or may not have a year code, but the circuit board date code is visible at 8:48, between the looped wires above the tube socket -- 24th week of 2007. So the amp itself probably shipped late 2007 -- maybe a Christmas present? That's of interest only because of the talk near the beginning about the particleboard cabinet era. There's another marking, a Pb-Free symbol between the tube sockets, which means there's no lead in the surface finish of the bare PCB, or in the assembly solder. That might work against the long-term reliability of those board-mounted tube sockets, but if the soldering was done correctly the difference should not be that great. In any case, almost all electronic products sold worldwide need to be lead-free, so it would be no worse than a competing amp from the same time period. The build quality does look surprisingly clean, as mentioned. I'm sure many of us were expecting "spaghetti factory" wiring, but it's tidy as hell.
A few thoughts, maybe they'll be helpful: - I agree with others who said "change speaker" as a first step with this amp. I have a Valve Jr, and the stock speaker sounded really dark in mine. Plugging the amp into a 2x12 cab with Scumback speakers (no changes to the amp) brought the amp to life, and made me question whether any circuit changes were actually needed (but I haven't dimed the amp volume either). - Having C6, R10, C9 and taking voltage for the output tube from C9 reduces hum. You might not notice with the 8" speaker, but when folks build homebrew Champs with 12" speakers they wonder why the amp hums so much. It's because the bigger speaker can reproduce the hum that was always there. Single-ended OT's don't cancel hum at the output stage the way push-pull OT's do, so the extra stage of filtering is often helpful. - The amp definitely sounds improved after your changes. Maybe the "brittleness" you're hearing is grid current when the EL84 is being slammed when the volume is full-up. This could happen when the peak input to the EL84 exceeds the bias voltage. Your rebias adjusted that voltage from 10.7v to ~13v, so the EL84 could take more before running into grid current. Perhaps increasing R15 to limit grid current might be a step in the right direction. - Related to the output tube drive/grid current, do we really need all the gain (I mean "voltage amplification") available? R6, R7, VR1 previously applied 1/3 of the 1st stage's output to the 2nd stage grid. Assuming a gain of 60 for each of the preamp stages, a 100mV guitar signal would be 6v at V1A's plate, 2v at the output of the (max'd) volume control, 120v (!) at V1B's plate. Now that's applied to an EL84 grid that only has a bias of 10-13v. Maybe a voltage divider between V1B's plate & the EL84 grid (along with maybe a larger grid stopper on the EL84) could be something to try? - Kudos on the re-bias! I ought to change mine in a similar manner. Sure, the tube lasts okay, by why not help it last longer? The voltage outputs above are just a guess; you'll actually want to hook up your meter to verify they're really happening in your amp. I'm thinking you might find a balance you like between driving the 12AX7 stages hard vs driving the EL84 hard if you safely rig up a volume control between V1B & V2, where you get grind without the harshest grit.
Thanks for the comment. I did increase the R15 value at one point. Looks like I forgot to mention that in the final summation, but you can see it's been changed to a 15k at 37:20. I can appreciate what you're saying about a bigger speaker perhaps expressing more noise than an 8", but a new speaker or cab wasn't going to solve the brittleness issue I was hearing. I feel like I got close in the end. In some amps, I like a bit of unrefined grit in the tone to add character, but in this instance, it was overpowering and rendered the amp uninspiring to play. Thanks again for the thoughtful comment! I know others will benefit from it.
I often make guitar amplifiers with EL84 and ECC83. I like clean tone on the edge of the distortion rather than the fuzzy tone. I did many changes until I found a good solution. Here is my scheme and on the right scheme is as a option variable negative feedback and presence control but I prefer the amplifier sound from the scheme on the left. Greetings from Croatia! elektrotehnika.simplesite.com/434348419/4759357/posting/poja%C4%8Dalo-za-gitaru-5w-sa-ecc83-i-el84-samogradnja
Nice video! Good to see all the process. A Eminence factory tour would be cool. Did you change those 12ax7 bypass caps from electrolytic to regular caps? And why?
I LOVE my Junior......It has impressed so many guitarists over the years. I still remember the day back in 2005 as I was walking out of a Marshall Music store.....just before the door, I looked way across the room to see my Junior sitting on top of a half wall.....all by itself. I couldn't get it home fast enough after hearing it. I have heard others that do not sound like mine. Mine is very punchy with no brittle tone.
Sounds good, man. I have the head version with the matching cab. (12" Chinese fake Eminence crap as opposed to 8). When I first got the head, the preamp was a new EH 12ax7. Swapped it out for an old RCA ax7 and that killed a lot of the brittleness. Before that, I'd tried an old GE 12au7 (more clean headroom than I've ever seen in a 5 watt amp). Next thing I plan on doing is putting a decent speaker in the cab.
Your work's inspiring. I'm really enjoying learning tube theory, definitely something that was not covered in my electrical engineering classes, even in the late 90's.
Cool video, but you're lost on a few things. C4 is not 'adding lows'. A bypass capacitor like that passes all highs first, then, the larger the value, the further the frequency range extends down. R6/R7 and the Volume Pot form a voltage divider network. Taking the output of V1A and cutting the amplitude back to 1/3 as to not overly distort V1B. Weird / bad design, but you can see what they were trying to accomplish. I like your mod there though, will probably use it myself. R10 and R11 form a voltage divider. C11 is is paralleled with C8 for noise rejection -- large value electrolytic caps have internal inductance from the circular design which prevents high frequencies (noisy hiss) from being filtered out, which is why you parallel them with smaller value caps that have lower internal inductance and can filter that noise.
Didn't scroll through all the comments to check if anyone posted this, but that fizzyness (at least for my valve junior) was to use a 5751 instead of a 12ax7.
I do believe R11 is a burden resistor. It drains voltage off the big caps. The benefit of deleting R10 is two. 22uf caps filtering in parallel. Effectively 44uf to quiet the amp. Kudos for doing your own thing. The amp was already a little. growler. But there are better choices that give this little amp a lot more flexibility in voicing.
Oh boy what an improvement. I have an old 5w Epiphone Valve Junior Plus. It's basically the same amp but with a 3 band EQ and a standby switch. I should pull it out and have a look inside.
Interesting video, thanks. I see I am a bit late to the "It's a bleeder resistor" train from the earlier comments! I wondered if you siliconed those components down afterwards? I'd be worried about that ceramic 5w plate resistor shaking loose and damaging the tracks on the board. Thanks again.
Hey dude! I live in Bowling Green, KY. I play at Cafe Coco a lot. I love your vids! Thoughts on the Peavey Windsor? I use it myself and love it, but I'd love to see you take one apart. Thanks!;).
Biggest differences in tone were from replacing that 1M series resistor and changing out the stock speaker. A lot of the "brittle" tone came from thermal and shot noise in that resistor, and the Lady Luck was one of Eminence's biggest mistakes. You never actually put any high snubbers in this, but if I were to do so, I'd do what Marshall did and put them across the plate resistors. To the AC signal, HT is as much of a ground as the 0V rail.
I’ve been watching your videos for a long time and I think you’re brilliant lol would love to know the basics. Could you recommend a book or anything to get me started?
Not sure why you didn't know the 220k was a drain resistor? Also, very common power supply circuit using a resistor rather then a choke which could have been replaced with resistor of increased wattage and put back in based on color changes to the old one.
When I was first starting out doing this, I read somewhere about it not being ideal to have a power node supplying nothing up front. I don't see a need for it. The 220k dropping resistor was unnecessary. The two 22uf caps now double the cap value on the first node, which I like better. You are right about the 220k to ground. That isn't a common thing in vintage amps, which is what I was visualizing while fiddling with the power circuit. Brain fart on my part. BUT, I'm going to make another video showing the cap drain times with and without that resistor and see if it's even necessary. My hunch is, the conductance of the still-warm tubes as they cool after power down will be enough to drain all caps in a reasonable time without that resistor. We'll see.
Hi, The warm tubes will bleed off the main caps with a power down as you have stated. However, if you or someone less experienced is trying to servicing the amp and for some reason the tubes are not in at power down, there is nothing to bleed off the HT so personally I would leave it in for safety reasons. Also the grid stopper resistor should be physically located as close as possible to the grid to reduce the possibility of any unwanted oscillation.
Talk about a waste of time. There goes 43:35 that I will never get back In life. This long winded guy who likes to hear his own voice could have summed this is up in 5 minutes. Worthless.
i build tube amps ,the el84 is not a glassy tube if it's treated properly,check the screen circuit,switch the cathode circuit,add triode pentode ultralinear switch.i just built a little amp that uses a 6V6 and 2 12ax7s and one 12AT7,it has full proper reverb feeding a 9" tank,NO eq but the power amp is super smooth,there is a rc network in the preamp to tame the highs a bit,and band width focusing is done in the pre amp,so no eq is needed,so the guitar can set eq.Along with triode ,pentode and ultralinear modes,the tones can be tailored to suit any style,super clean to thrash. The chassis is the same as the one in your vid,and it's point to point built with every scrap of space used for circuit,seeng as there is so much circuit in it. This amp was an experiment to see if i could cram it into a tiny chassis without noise,and i did.. At some point i will be posting youtube vids of it and a couple of other amps i have here.
Alright, so I'm like three months late, but I actually did the mods you showed to my Silverface Champ (Yeah, I have no respect for the past. Sue me.). I had already bypassed the tone stack, but changing out the bypass caps and adding the grid stopper resistor helped it handle the ungodly amounts of distortion I like to throw at it. Much less fizzing, much more roaring. Thanks for the info!
I have the separate amp version of the VJ, and since I don't know anything about electronics, I modded mine by connecting it to a 2x12 speaker cabinet. That made it sound quite good. Don't ask what the speakers are. I've had that cab for quite a while.
kinda funny the whole time I was thinking what about the speaker, if it had been me I would have started there. The only reason is in my experience I've often found that the factory uses a thin baffle and short screw so they have to torque it so tight it can do ugly things to the tone of the speaker as well as being a cheap speaker. I just sold my head of this amp which I always used with a 12" speaker which gave it a little more bottom end. thanks for another great video
A few months ago, on a lark, I bought the head version EVJ at Guitar Center for 90 bucks. I stuck some good tubes in it and run it through a 12" Celestion Alnico gold speaker I have in a spare cabinet.. It sounds pretty darn good. It still needs some mods as it doesn't quite have that EL84 sparkle and chime as my Gibson Super Goldtone does and it's not a blues machine like my AB763 Super Reverb, but for under a hundred bucks, it was a no brainer.. I think however getting the head version and running it through a good 12" speaker (or two) would make a huge difference in it's tone, punch and tightness.
Here's the follow-up video: th-cam.com/video/xMpWcFX4wAg/w-d-xo.html
Love the walk through... good knowledge - great little practice amp now.
LOL - the power supply filter caps - THEY GO TO 11!
I would like to point out that the number 10 is considered unluck by the chinese. Something about the characters that make up the number 10 mean "bad luck" or some such.
purplexenno, ln the Philippines they're like that too, and do "o"s.
Marshall has been using 'cardboard' for their cabinet back panels since the 70s. I'm sure it was a cost savings move, but MDF also has desirable sonic qualities (lack of reflection) as a back panel. Also, like most amps, it's wrapped in tolex and therefore quite unlikely to fall apart. At the least, "you get what you pay for" logic certainly does not apply to this example, as 1960 cabs are not inexpensive. Not to mention, for many years, these 'cardboard' cabs were made in England. Many MIC products (e.g., the Squier Classic Vibe series) will stand toe to toe with their more expensive, made elsewhere, equivalents these days. Many of them are rebadged products from other, american and European companies (the result of our sending our labor overseas for cost savings).
Just sayin', the well worn absolutes are far from absolute...
all these people chasing the jimmy page tone and this little amp nails it.
He did use small valve amps in the studio.
The circuit, tubes and transformers that make of the amp are not bad at all. The real limiting factor is the 8-in speaker which makes it overall 'tinny' sounding.
You can actually manage to fit a 10-in Alnico speaker in there and it clears the tubes and transformers. popular are the Jensen P10 and Eminence 1028k. You do have to dremel a bit of the bottom of chassis and make a new speaker baffle, but this is an easy hour-long project on the weekend.
Really wakes the amp up and it's still beautifully compact
Had a few of these as spares it does nail the communication breakdown tone I'll give it that.
"100 bargain basement amps"
-J. Page
Did Jimmy play his stuff on that amp.
The first difference in improving the sound is made by the speaker - Thanks for great job
The speaker used judging by the basket stamping is a Rola USA alnico . By 5his time Rola UK had bought Celestion and used large cylindrical alnico magnets.
Brad, I really like your channel and took away a real nugget from this Valve Junior mod video. As you reviewed all your mods, the one that didn't get any "air time" was the Zobel network across the output transformer. I design low-watt but high gain single-ended amps w/o global feedback. I can tame oscillations just fine but that "fizz" remains. The "ah-ha" moment was seeing you add the Zobel. I immediately clipped in 10R/50nF across the speaker and the results are amazing. Many thanks for the tip.
What do ur little. Amps go for? For a fellow guitologist fan ??!!
"disregard the noise, but let's listen to the tone... KSDHFHAWIUFEACKDJFA how about that for tone?" hahahahaha I think I woke up the whole house laughing. made my day. I love your channel, man. I've watched a bunch of your videos and I just want to build an amp now, you're doing a great job at demystifying this trade, your playing is fantastic, your commentaries are insightful and your love for tinkering is contagious. Cheers!
hahaha...yeah I knew that was gold the minute it happened. Thanks for the kind comment. Glad you enjoy the channel. Good to have you.
Haha same here!
You can be Brad Ramone in the New Band with that TONE!!
I'm an amp tech also and I really like your videos you are very practical and use common sense and logic. I have been repairing electronic equipment all my life and I am not to vane to admit I learn from you . thanks for the great videos.
absoloutly go to the eminence factory please!!! love watching what you do.
I would also like to see a scrapper amp build or builds using parts from various common "junk" equipment. instead of converting, rather using salvaged parts to create something completely different.
I have so much crap on my graveyard pile, it'll happen. Stick around.
Yes Eminence factory tour Please
I think it could be hilarious if you toured the plant and told them all about how the factory in China, you know the real one, does things. You could just make up a bunch of crap about them, what are they going to do after all? Just think of all the cost saving advice you could offer, lol.
Eminence factory tour please!
@@TheGuitologist cool I hope you find the time.
Love these things, got the head version. Only did one mod so far to boost the volume. And added two 4ohm speakers for portability without added cab. Great stuff. Good comments. Awesome results as usual Brad. Thank you again
32:00 The 220k is for discharging the capacitors when the amp is turned off to prevent shock, and the .1 was a bipass cap.
You are correct on the resistor. I'm going to make another video testing discharge times with and without it in place. But the cap... It's on the power side of the plate resistor. I see there's an RC network set up by the plate resistor and that cap, but the fact that it's in parallel with a much large power cap makes it seem a bit pointless. Usually when you see those, you see an extra dropping resistor separating it from the larger power cap on the rail.
Here's the follow-up video: th-cam.com/video/xMpWcFX4wAg/w-d-xo.html
the small cap is there for bypassing HF
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The 22uF/220R/22uF circuit is a CRC filter to reduce hum cheaply, instead of using a choke. You could use 47uF/100R/47uF for better filtering and less sag. The 220k resistor is a SAFETY MEASURE, it's used to discharge the B+ caps, PLEASE put it back!!!
Absolutely, there is nothing to discharge those capacitors without that resistor aside from the very low leakage current. If you think it's going to affect tone, you can put in a bigger one so the caps discharge more slowly, but don't take it out.
Thanks for the comment! You are correct. My brain was farting out at 3AM again, got tunnel vision visualizing a typical Champ power supply. Vintage amps don't typically have drain resistors. The conduction of the tubes as the amp powers down usually takes care of smaller value caps like this, no problem. In fact, I should make another short video of the cap discharge rate with and without the resistor in place. Should be informative. My hunch is, it's a measure designed to clear regulations rather than actually discharge these caps, but I could be wrong.
If something happens to the tubes, like, the filament opens, or some other damage that stops them from conducting current, or you test the circuit without the tubes in, there's always a risk of shock right after turning everything off. The resistor is a very simple and effective safety measure to greatly reduce that risk of shock, and it only uses a few miliwatts off the B+.
Always better to have a resistor discharge a capacitor rather than yourself doing that job.
Here's the follow-up video: th-cam.com/video/xMpWcFX4wAg/w-d-xo.html
Just ask Brad, my email signature is "Discharge the caps? Oh......I think I just did."
I bought an Epiphone Valve Jr and after modding it a bit I had the same issue that it sounded to fizzely for my taste. After asking a fellow amp tech we changed the R15 resistor from 1.5k to 100k Ohm. His reasoning was that the pre-amp creates too much amplification for the grid of the EL84 and by increasing R15 it could become smoother over all. We've tried it and it was instantly better.
Additionally we added a "Bone Ray / Roy Bean" tone stack after the volume put which made this amp super easy to dial in now. There is a book "Designing Valve Preamps for Guitar and Bass" by Merlin Blencowe which had the schematic - I couldn't find the schematic on the web. Essentially its a Tilt and Middle control which is quite effective and offers quite a variety of sounds.
Also I hook it up to an Eminence Cannabis Rex 12" speaker and it sounds wicket cool - or at at least a lot better than before :)
Oh I found it el34world.com/Forum/index.php?PHPSESSID=3ab430srvh54b23l336mecrk23&topic=16837.msg167081#msg167081
That's cool! I almost think that your modified version and a regular version would sound dope together like a mini stack!
If anyone is wondering about the purpose of some of the removed components. The resistor to ground in the power supply was there to slowly discharge the high voltage after the amp is turned off, it is a safety feature. The small capacitor in the power supply that is in parallel with a much larger one is there to handle high frequency ripple since the large cap has a high inductance. I would have left those two parts in place.
I can't imagine seeing a resistor in an amp that has seen enough current to scorch it and think "I'll just remove it and add a jumper. That will be fine." 🤣
Your videos are very inspiring. I built my own amp from a kit about a year ago and after making a few tweaks and mods, I've realized I like messing around with a circuit even more than I like playing guitar. Just ordered my second amp kit and looking forward to that experience again.
Awesome job Brad! I loved your attitude going into this. For what it's worth, I think it sound pretty good at the end. My first amp ever was a 15 watt solid state Fender amp with an 8" speaker. Since then, I've pretty much always preferred amps with 12" speakers and I suspect that this amp would sound pretty good through an open back cab with a low wattage, vintage voiced 12" speaker (or a pair of them). I'll check out the follow up video too.
That's what I was thinking also. The speaker is definitely the worst part of the combo in its original state.
My first amp was a similarly cheap tube amp combo with a cheap 10" and as soon as I hooked it up to a quality 12" speaker I stopped being as concerned about getting a new amp. It was a whole new world of tones.
Re. speakers for these, I put a 'Celestion Eight 15' in mine, which is a good improvement over stock.
Brad, with me being a guitarist/amateur guitar tech the stuff you do with amps is firmly in the realm of 'give it to someone else to fix', for me. But fascinating to watch and strangely addictive. Thanks for posting, keep it up.
Me too, but on a $100 amp, may be worth the risk. Fun to try
Modified versions of this amplifier can sound fantastic, the modifications to the power supply though in particular are random and ill conceived. You bypassed a resistor that is a section of an RC filter, you also removed a bleed resistor not even knowing why it was there. The 0.1uF capacitor across the 22uF is a common approach to mitigate self resonance that aluminium electrolytics are known for, it is not a great engineering solution. Randomly removing the capacitor likely had no effect at all.
😂😂him so smart 🥹😱
The high value resistor that was removed from the power supply (where it was in parallel with the caps) was a safety feature, meant to drain charge off of the caps after the amp is turned off.
R11 is a bleed resistor for those BFC's in the power supply. C11 is a high frequency filter cap to reduce noise going into the preamp stage.
I've gone through most of your videos once and am going back over many for a second and even 3rd time or more, al a fantastic bandmaster to JTM conversion. Just ignore the occasional A hole and keep doing this. We love you dood...
I know this is older but this just popped up in my suggestions. Super cool man
love watching your vids...even though i dont know what your talking about. maybe im learning subconsciously?
Osmosis is a good way to learn. But don't always take my word for it. As others pointed out in the comments, I don't always know what I'm talking about either. Brain farted on the power supply on this one.
yup.
STEVE LEITNER check out Uncle Doug's channel for some excellent basic tutorials.
Love me some Uncle Doug & Rusty.
STEVE LEITNER you read my mind. :)
Great channel ! Especially the dumpster finds. More bass gear please. I don't understand the the electronics but I know what my ear tells me. The little Epiphany amp sounded awesome after your mods. Cudos
New to your channel, love this content! Keep it up dude, this is a niche video type, but it certainly has an audience.
Thanks, man. I need the encouragement! :D
A 10 inch speaker would solve the fizzy tone I think. Great job for only a few parts. Your idea about a small Pico cap to ground or screen to plate works. I did this on an Orange Dark terror. Even across the plate resistors which I dont normally like to do, add a 100pf or 200pf there and trim off those fizzy overtones.
I used to have the head version of this, and I ran it through a Marshall 1960B 4x12 with 4 75 watt celestion GTs, it sounded amazing when you cranked it all the way. I don't know anything about messing with circuits like this, but i really want to learn. Love your videos. It seems like a super-valuable and handy skill to be able to modify electronic circuits instead of having to be at the mercy of manufacturers like the general public. Thanks for making these videos. It was super interesting to see how the tone shifted based on the capacitor and resistor changes you made. I'm learning a lot...
I was so glad to hear those two magical words: SPEAKER 🔊 REPLACEMENT.
The harsh buzzy overtones when it's dimed out, ugh. I have best luck with humbuckers on this amp, neighborhood of 5, cleanish rhythm sounds. Single coils, I gotta run it through eq or the bottom end disappears. Bought mine in 05 or 06, I think it's the first version of the circuit. I've run the speaker in the cab on a very similar low powered Hughes and Kettner tube head from the early 90s, and I'll tell you, the speaker and cab aren't what's lacking. I'm in the middle of your vid as I write this but I think your mods are on the right track. I know nothing and play even less, but thumbs up.
Great video as always. Please keep them coming. Thanks for giving up your time for us to learn.
Sounds great! A buddy of mine totally redid my Junior 10 years ago, hand wired on a new board...and it sounds very Vox-y. I run mine through a 1x12 loaded with an EV speaker. It just kills. Great vid, as usual!
Cool video 👍 I like your laid back attitude
Thanks, man. I like that you like my laid back attitude. :P
Wow! I just started watching your vid on an amp mod,then I hear you demonstrating its tone prior to mod.your guitar skills are top shelf;the speed and fluidity you possess floored me,especially when I saw you only run with three fingers.Bravo!Keep it coming,please.
Thanks for the compliments. I appreciate that.
J
the j
Fast forward 5 years from this video...The "Guitologist" mod for the Valve Junior is now world renowned
You are a mad genius!!!! I wish you could get your hands on my Epiphomne Blues custom 30! I bet you could work magic on it. Great video!
Another small note, the 220 ohm in the power supply isn't to drop voltage as much as with the cap before and the cap after is for filtering.
You are right. It's part of the filtering network. I only mentioned the voltage drop because I'd already decided to eliminate it and figured it wouldn't affect the voltage at the OT node much at all.
Volume control seems to be an unnecessary luxury option. Most of us probably have a volume knob in the guitar. 😀
Old alnico speakers, if they are in good condition, are sometimes real gems. I have a late 50's very elliptic shaped Rola alnico speaker which sounds just unbelievably good.
And with these two tube amps, if you want different, more relaxed clean tone, try 12AT7/ECC81. I just recently tried a brand new JJ ECC81 instead of 12AX7 in one of my amps and it sounds absolutely great when playing at clean volume.
My brother modded one of the Valve Junior Amp heads, then he built a speaker cabinet to go with it. That setup sounds amazing !
Subscribed! Very relaxing and info-loaded videos
Welcome aboard!
I had this amp when it was new. Owned it for a looong time as my only amp, with just some pedals. Remember saving cash for this to replace my first amp which was a little 15 watt ss crate. Thanks for posting this video! Now I wish I've still had this thing.
5:00 I'd love to see you do a tour of the Eminence factory, while we still have a couple things being built in the US
Better audio quality in sound examples will be an asset to your (great) uploads in the future.
So this amp goes to 11? You know when you need that little extra it goes to C 11. Amazing looking build from the factory. Love your videos. I can even sing let alone play a instrument.
Gotta love Pyotr Belov's amp designs. I've got a custom one-off build he did, and have owned a number of his designs (Epiphone VJ, SoCal, Blackheart Little Giant, etc.) and have always thought the quality was far beyond the price point. That, and as a mad scientist, he builds most of his designs to be modded.
Never heard of him before you mentioned him.
I once had a Harley Benton 'clone' of this, the GA-5. That was cute and did have an extra knob on it.
I like the GA-5 a lot, sounds great with my Squier Tele
What an improvement! Great job :) Thanks for making these videos, I really enjoy them.
Just wanted to say that I successfully installed an Eminence 1028k speaker in one of these. some dremeling and new speaker baffle was made with the original grill cloth stapled onto it, but it totally worked.
in conjunction I made all of the resistor changes in this vid, opted for Mojotone Dijon capacitors of same stock value. They really tame a lot of the brittleness inherit in this amp. 150pf ceramic 'bright cap' on the left and center lug of the volume control to "open it up" a little bit at lower volumes.
It's so perfect as is now, I'm afraid to modify it any further.
Big fan of your channel here. I just got me a blues Jr for $40 dollars after watching your video, and I am going to do these mods.
Being pleasantly surprised by plywood...what a world
The first cap/resistor/cap arrangement straight out of the rectifier is called a PI Filter. It’s there to lower the ripple (hum) on the power supply. I prefer replacing the resistor with a choke as you get less sag, and a better filter to clean up the power supply noise.
The 0.1uF cap on the power supply is there because big electrolytic caps have poor HF performance.
The 220k to ground is so your power supply can safely discharge when the amp is off.
r11 is to drain the voltage when the amp is powered off. r10 in combination with c9 forms an RC filter for less hum. Edit: C11 is for high-frequency bypass, where C8 is for lower frequency bypass
the speakers on guitar amplifiers attributes a massive amount to the tone of your guitar amplifier.
Johan Segeborn has some great videos on the subject and everything marshall,
Mr Wampler(yes the guy who makes awesome pedals) also demos 10 amplifiers through one cabinet
to show how much several different amps sound very similar when using the same speaker.
The CE marking means "European Conformity", basically the same as an FCC marking here in the USA. Only thing is with the PRC which has humorously decided to use a near identical marking for "China Export", which is officially an unofficial marking so the EU can stick it.
Eventually the people living under the EU will realize it isn't doing them many favors.
Hello from Washington State.....and thank you for the video. I was forced to open my Epi valve Jr. (head) as I left it on overnight to a failed condition. And...now need a schematic....found by your hand to what I now study for repair end goal.
I use the unit as source by fender frontman to Fender Cab. And, I really like the warm tone. Just a bit of hum...but I find the crunch input is remarkable at higher volumes and what I enjoy from a Jackson set of pickups.
And, at unit open, first test run...did not find the failure. So I am studying the
values to continuing test and intended replacement. With no hurry, routine
repair (and or replacement).
I might be that person looking over you shoulder....and liking the clear presentation of mods...best avenue to improved performance as I am working to repair+ end damaged finding. I like the absolute best value as job process and reliable use.
just watched your video, it was fun. I actually just gutted a valve junior to make a small trainwreck with the chassis. It was a very good lesson for people starting out. You explained everything you did very well step by step for your audience. At the end of the video you layed out all your changes and you added the fact of a zobel network , but you never went over that in your video, some of them might not know what it is or why you did it. Good job and keep on building.
Boy you get a lot of comments fast, don't you. Nice video, Brad. A Valve Jr. was my first build (built it in a computer power supply as the chassis). I've hardly used it since I built it. Just not a great sounding amp. I like what you've done with this one, though. I might do a rebuild of it...
That speaker at about 30:35 is Best brand (EIA code 371).
I have an Epi Valve Jr Head plugged into a speaker that came from a late 1970s Fender Twin Reverb that is mounted in a Pine Cabinet that my wife built. At full volume it is loud. It is full. It is not fizzy. It is hard rock and roll. And in my small music room it is very easy to control the feedback and sustain endlessly. When I have it set to about 9 and run my guitar in stereo thru an analog chorus with my Dual Showman it sounds as pure and clean as any stereo. I am looking to buy a few of these and replace the electronics with some fiberboard mounted components just for grins.. Sort of trying to teach myself the dying art before I croak! Thanks for posting your videos, I glean a lot from them.
The 220k 2/3W to earth is a power cap drain resistor and is common in many amps but usually sits before the first cap stage . The use of one cap with no power node is purely for filtering and is very common . The resistor between the 2 will be a wirewound and will act like a choke not drop any voltage . This is left over from the days when small amps had a 1k 25W choke driving the speaker straight from the first cap , like the Valcos ( Oahus) and Gretschs 6155s etc of the 50s . Kind of like the standby switch , totally unecessary but traditional. 1 22 uf filter and 3 x 22uf caps are plenty for this amp and more than the original Vox AC4 with a 12ax7 trem tube . The weird one on the end of the chain is a mystery unless a solid state LDR type trem version was planned as small value electrolytic caps are often found in those trem circuits . The speaker is a Rola alnico going by the basket stamping . Rola UK used the same baskets but large cylindrical alnico magnets and by the 50s had bought Celestion who produced them at Thames Ditton or in London before moving to Ipswich . The 10" ribbed cone variety works great in pairs , but are very nice as singles too .
Craigslist’s in America, gumtree in Europe, love your videos man, thank you
Great job! I was wondering what you think about the Monotone Stage Right 5-watt amp?
Great video, as usual! A video like this about the epi blues custom 30 could be also very interesting.
I have owned the Epiphone Valve Junior 5 watt combo with the 1x12 cab and I loved it. One of my biggest hurdles of practicing is my constant tweaking and fiddling with the knobs to try and get that "perfect" tone. With pedals, amp and guitar, just too many things to try and tweak. This eliminates a third or those temptations. My guitar has a single humbucker with one volume knob. There's another third gone. Simple and sweet. With a Gibson SG and a Mesa Boogie Mark V, I am paralyzed with options!
Not saying this applies to you at all, but I used to manage a music store and one of the most eye-opening things for me to witness was the sheer number of people who were, to put it kindly, very BAD at guitar, yet who would come in to test drive a Mark V or Road King II or something, thinking that a better amp would make them better players. Nothing wrong with wanting good tone as a starting point for improvement, but it seemed more like they were looking for some shortcut to avoid 10,000 hours of practice.
you mean, there isn't a shortcut to practice? What if I spend more money and get more pedals and whatnot?
lol I know you were being sarcastic, but what you said is very true. Many guitarist (me included) think that new amp of pedal will fix our shortcomings, so we spend truck loads of cash like it will be the magic fix. Well, it don't quite work that way. And not just jamming along side a backing track (like I do)
spend more money, get a color you like - drink lots before you play - and get the new boss "talent " pedal ,,,,works great !!
Would have liked to hear it into a bigger cab, 15" single, maybe a 4×12.
I use this amp with Marshall 1936 2x12 cab. Its killer amp, dont know why people frown about it.
I used to have the mini stack. It was all ply and looked great. It was a bit quiet and a bit dark (I used to use it with a homemade rangemaster). I had to source and fit a replacement output transformer after it died mid practice. I liked how it had a 'proper' pot after the nightmare blues junior pots.
I now have a Laney cub10, it's just beautiful sounding, and LOUD!
I just got into your channel and love it. I just bought the Epiphone Valve Jr Head it came with a Sunn Tranducer 1216G speaker versus the Eminance stock speaker should I be concerned or is that an upgrade. I think that amp has been modified it certainly has been opened.
I got crap practice equip, so I should say that this ampo rocks, and you being able to actually play good guitar makes it sound great :)
I just bought the head version of these with some nicer tubes and a late 90s fender 1x12 cab. If I'm honest I'm blown away by just how loud it is and how good it sounds. I originally bought it as a toy to mod by my opinion has been changed and it will become a rehearsal amp for sure. I hate to rant but I'm excited haha. I'm also surprised at how incomparable the tone of the TH-cam reviews I've seen is to my amp.
nice bro..diggin your vids..got one of those Lil Dudes, loved it as is...but dayyyyum...You near Lex Ky?
As for dating this amp, the serial # may or may not have a year code, but the circuit board date code is visible at 8:48, between the looped wires above the tube socket -- 24th week of 2007. So the amp itself probably shipped late 2007 -- maybe a Christmas present? That's of interest only because of the talk near the beginning about the particleboard cabinet era. There's another marking, a Pb-Free symbol between the tube sockets, which means there's no lead in the surface finish of the bare PCB, or in the assembly solder. That might work against the long-term reliability of those board-mounted tube sockets, but if the soldering was done correctly the difference should not be that great. In any case, almost all electronic products sold worldwide need to be lead-free, so it would be no worse than a competing amp from the same time period. The build quality does look surprisingly clean, as mentioned. I'm sure many of us were expecting "spaghetti factory" wiring, but it's tidy as hell.
Good points...especially about the lead free solder.
A few thoughts, maybe they'll be helpful:
- I agree with others who said "change speaker" as a first step with this amp. I have a Valve Jr, and the stock speaker sounded really dark in mine. Plugging the amp into a 2x12 cab with Scumback speakers (no changes to the amp) brought the amp to life, and made me question whether any circuit changes were actually needed (but I haven't dimed the amp volume either).
- Having C6, R10, C9 and taking voltage for the output tube from C9 reduces hum. You might not notice with the 8" speaker, but when folks build homebrew Champs with 12" speakers they wonder why the amp hums so much. It's because the bigger speaker can reproduce the hum that was always there. Single-ended OT's don't cancel hum at the output stage the way push-pull OT's do, so the extra stage of filtering is often helpful.
- The amp definitely sounds improved after your changes. Maybe the "brittleness" you're hearing is grid current when the EL84 is being slammed when the volume is full-up. This could happen when the peak input to the EL84 exceeds the bias voltage. Your rebias adjusted that voltage from 10.7v to ~13v, so the EL84 could take more before running into grid current. Perhaps increasing R15 to limit grid current might be a step in the right direction.
- Related to the output tube drive/grid current, do we really need all the gain (I mean "voltage amplification") available? R6, R7, VR1 previously applied 1/3 of the 1st stage's output to the 2nd stage grid. Assuming a gain of 60 for each of the preamp stages, a 100mV guitar signal would be 6v at V1A's plate, 2v at the output of the (max'd) volume control, 120v (!) at V1B's plate. Now that's applied to an EL84 grid that only has a bias of 10-13v. Maybe a voltage divider between V1B's plate & the EL84 grid (along with maybe a larger grid stopper on the EL84) could be something to try?
- Kudos on the re-bias! I ought to change mine in a similar manner. Sure, the tube lasts okay, by why not help it last longer?
The voltage outputs above are just a guess; you'll actually want to hook up your meter to verify they're really happening in your amp. I'm thinking you might find a balance you like between driving the 12AX7 stages hard vs driving the EL84 hard if you safely rig up a volume control between V1B & V2, where you get grind without the harshest grit.
Thanks for the comment. I did increase the R15 value at one point. Looks like I forgot to mention that in the final summation, but you can see it's been changed to a 15k at 37:20. I can appreciate what you're saying about a bigger speaker perhaps expressing more noise than an 8", but a new speaker or cab wasn't going to solve the brittleness issue I was hearing. I feel like I got close in the end. In some amps, I like a bit of unrefined grit in the tone to add character, but in this instance, it was overpowering and rendered the amp uninspiring to play. Thanks again for the thoughtful comment! I know others will benefit from it.
I often make guitar amplifiers with EL84 and ECC83. I like clean tone on the edge of the distortion rather than the fuzzy tone. I did many changes until I found a good solution. Here is my scheme and on the right scheme is as a option variable negative feedback and presence control but I prefer the amplifier sound from the scheme on the left. Greetings from Croatia!
elektrotehnika.simplesite.com/434348419/4759357/posting/poja%C4%8Dalo-za-gitaru-5w-sa-ecc83-i-el84-samogradnja
Nice video! Good to see all the process. A Eminence factory tour would be cool. Did you change those 12ax7 bypass caps from electrolytic to regular caps? And why?
You only need electrolytics in that position for higher values. Polarization isn't necessary there.
Haven't heard a valve junior for about a decade !! Used to own one. Nice video !
I'm shocked at how good that little thing ended up sounding!
I LOVE my Junior......It has impressed so many guitarists over the years. I still remember the day back in 2005 as I was walking out of a Marshall Music store.....just before the door, I looked way across the room to see my Junior sitting on top of a half wall.....all by itself. I couldn't get it home fast enough after hearing it. I have heard others that do not sound like mine. Mine is very punchy with no brittle tone.
Another pedal slayer! Well done Brad, I cancelled cable tv, your my favorite show! Good playing also.
Digital cable is free now (for the price of an antenna), but I still would rather watch this!
*you're
Sounds good, man. I have the head version with the matching cab. (12" Chinese fake Eminence crap as opposed to 8). When I first got the head, the preamp was a new EH 12ax7. Swapped it out for an old RCA ax7 and that killed a lot of the brittleness. Before that, I'd tried an old GE 12au7 (more clean headroom than I've ever seen in a 5 watt amp). Next thing I plan on doing is putting a decent speaker in the cab.
Thanks for sharing your experience. Every little bit helps the knowledge base.
Your work's inspiring. I'm really enjoying learning tube theory, definitely something that was not covered in my electrical engineering classes, even in the late 90's.
Thanks for watching!
Cool video, but you're lost on a few things.
C4 is not 'adding lows'. A bypass capacitor like that passes all highs first, then, the larger the value, the further the frequency range extends down.
R6/R7 and the Volume Pot form a voltage divider network. Taking the output of V1A and cutting the amplitude back to 1/3 as to not overly distort V1B. Weird / bad design, but you can see what they were trying to accomplish. I like your mod there though, will probably use it myself.
R10 and R11 form a voltage divider. C11 is is paralleled with C8 for noise rejection -- large value electrolytic caps have internal inductance from the circular design which prevents high frequencies (noisy hiss) from being filtered out, which is why you parallel them with smaller value caps that have lower internal inductance and can filter that noise.
In Canada we have Kijiji. I had a valve junior and it helped me realize that I like Amps that compress and a class a amp is not for everyone.
Excellent approach to testing different values. I’m on the hunt for one to add a tube and the Vox Top Boost eq stage.
Didn't scroll through all the comments to check if anyone posted this, but that fizzyness (at least for my valve junior) was to use a 5751 instead of a 12ax7.
I do believe R11 is a burden resistor. It drains voltage off the big caps. The benefit of deleting R10 is two. 22uf caps filtering in parallel. Effectively 44uf to quiet the amp.
Kudos for doing your own thing. The amp was already a little. growler. But there are better choices that give this little amp a lot more flexibility in voicing.
Oh boy what an improvement. I have an old 5w Epiphone Valve Junior Plus. It's basically the same amp but with a 3 band EQ and a standby switch. I should pull it out and have a look inside.
With these -- the best thing to do is crank them and then use the tone and volume knobs on your guitar. If it's too toppy then roll it off.
Yeh brad !!! Get yer inner Paul kossof on !!!
Hehe it sounds a million times better
Cheers and Thankyou again for the great content
Interesting video, thanks. I see I am a bit late to the "It's a bleeder resistor" train from the earlier comments! I wondered if you siliconed those components down afterwards? I'd be worried about that ceramic 5w plate resistor shaking loose and damaging the tracks on the board. Thanks again.
Very enjoyable thank you from the UK and subscribed
Wow, really much better. Now keep your fingers crossed Gibson doesn't steal your improvements;)
Hey dude! I live in Bowling Green, KY. I play at Cafe Coco a lot. I love your vids! Thoughts on the Peavey Windsor? I use it myself and love it, but I'd love to see you take one apart. Thanks!;).
Glenn fricker of spectre sound studios raves about those as a cheap tube amp for metal.
The tour idea sounds good. Enjoyed the vid. Nice little amp.
I'm calling Eminence next week to see if they'll be cool with a tour.
Nice Improvement ....love the neck pickup sound especially
Biggest differences in tone were from replacing that 1M series resistor and changing out the stock speaker. A lot of the "brittle" tone came from thermal and shot noise in that resistor, and the Lady Luck was one of Eminence's biggest mistakes.
You never actually put any high snubbers in this, but if I were to do so, I'd do what Marshall did and put them across the plate resistors. To the AC signal, HT is as much of a ground as the 0V rail.
I’ve been watching your videos for a long time and I think you’re brilliant lol would love to know the basics. Could you recommend a book or anything to get me started?
I have book recommendations in the descriptions of my videos.
The Guitologist I should really start reading the descriptions lol Cheers 👍🏻
Not sure why you didn't know the 220k was a drain resistor?
Also, very common power supply circuit using a resistor rather then a choke which could have been replaced with resistor of increased wattage and put back in based on color changes to the old one.
When I was first starting out doing this, I read somewhere about it not being ideal to have a power node supplying nothing up front. I don't see a need for it. The 220k dropping resistor was unnecessary. The two 22uf caps now double the cap value on the first node, which I like better. You are right about the 220k to ground. That isn't a common thing in vintage amps, which is what I was visualizing while fiddling with the power circuit. Brain fart on my part. BUT, I'm going to make another video showing the cap drain times with and without that resistor and see if it's even necessary. My hunch is, the conductance of the still-warm tubes as they cool after power down will be enough to drain all caps in a reasonable time without that resistor. We'll see.
Here's the follow-up video: th-cam.com/video/xMpWcFX4wAg/w-d-xo.html
Hi, The warm tubes will bleed off the main caps with a power down as you have stated. However, if you or someone less experienced is trying to servicing the amp and for some reason the tubes are not in at power down, there is nothing to bleed off the HT so personally I would leave it in for safety reasons. Also the grid stopper resistor should be physically located as close as possible to the grid to reduce the possibility of any unwanted oscillation.
Talk about a waste of time. There goes 43:35 that I will never get back In life. This long winded guy who likes to hear his own voice could have summed this is up in 5 minutes. Worthless.
i build tube amps ,the el84 is not a glassy tube if it's treated properly,check the screen circuit,switch the cathode circuit,add triode pentode ultralinear switch.i just built a little amp that uses a 6V6 and 2 12ax7s and one 12AT7,it has full proper reverb feeding a 9" tank,NO eq but the power amp is super smooth,there is a rc network in the preamp to tame the highs a bit,and band width focusing is done in the pre amp,so no eq is needed,so the guitar can set eq.Along with triode ,pentode and ultralinear modes,the tones can be tailored to suit any style,super clean to thrash.
The chassis is the same as the one in your vid,and it's point to point built with every scrap of space used for circuit,seeng as there is so much circuit in it.
This amp was an experiment to see if i could cram it into a tiny chassis without noise,and i did..
At some point i will be posting youtube vids of it and a couple of other amps i have here.
Hi Guitologist, question on that Zobel Network: Where did you exactly solder it in?
I've got one - the valves got changed and I changed the speaker and it's much nicer with much more clean headroom. it's great for my practice needs.
'It goes _directly_ to eleven!'
Alright, so I'm like three months late, but I actually did the mods you showed to my Silverface Champ (Yeah, I have no respect for the past. Sue me.). I had already bypassed the tone stack, but changing out the bypass caps and adding the grid stopper resistor helped it handle the ungodly amounts of distortion I like to throw at it. Much less fizzing, much more roaring. Thanks for the info!
I have the separate amp version of the VJ, and since I don't know anything about electronics, I modded mine by connecting it to a 2x12 speaker cabinet. That made it sound quite good.
Don't ask what the speakers are. I've had that cab for quite a while.
kinda funny the whole time I was thinking what about the speaker, if it had been me I would have started there. The only reason is in my experience I've often found that the factory uses a thin baffle and short screw so they have to torque it so tight it can do ugly things to the tone of the speaker as well as being a cheap speaker. I just sold my head of this amp which I always used with a 12" speaker which gave it a little more bottom end. thanks for another great video
A few months ago, on a lark, I bought the head version EVJ at Guitar Center for 90 bucks. I stuck some good tubes in it and run it through a 12" Celestion Alnico gold speaker I have in a spare cabinet.. It sounds pretty darn good. It still needs some mods as it doesn't quite have that EL84 sparkle and chime as my Gibson Super Goldtone does and it's not a blues machine like my AB763 Super Reverb, but for under a hundred bucks, it was a no brainer..
I think however getting the head version and running it through a good 12" speaker (or two) would make a huge difference in it's tone, punch and tightness.