I’m getting addicted to this channel! So amazing! As a budding amp tech, I appreciate the different, yet practical approaches to these issues from the other magnificent amp repair channels on KZread. All of you guys are legends and are doing the world a service. As long as guitar players exist, these amplifiers will be coveted and expected to perform. But the art, and I do mean art, of amp repair is becoming a lost one. Those of us that seek to learn benefit greatly from these videos. Thank you, sir!

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Ryan, I appreciate your comments and I'm pleased you are enjoying the content.

@thebudgetguitarist9721

8 ай бұрын

Yep me too

We watch, We listen, We learn. Thank you Stuart.

@stuartukguitarampguy5830

2 жыл бұрын

My Pleasure. I also learn something from every amp I fix.

Cadmium plating on steel doesn’t make for a great ground point. Sanding the cad plating down to bare steel helped, but it can’t guarantee a lasting low-resistance ground because it won’t remain a gas-tight joint forever. Soldering the several ground points together was the right answer in my view… Your observation on star-grounds is also spot-on.

Thank you! Interesting analysis since I had a hum problem with a Fender Band-Master. I’ve ameliorated most of the 60 Hz hum by replacing a 7025 preamp tube that was new! I do follow Psionic Audio where I discovered the proper grounding systems. You are correct , you can’t just lump all the grounds together. Love your technique. Especially using the lead between the preamp section and filter caps as well as removing the tubes to isolate the origin of the hum. ❤

@stuartukguitarampguy5830

2 ай бұрын

Thanks I'm glad you liked it. The Psionic guy is very knowledgeable.

Note the patina of tarnish on the inside chassis ---- the area around the hole for the ground lug and mounting bolt should be cleaned with sandpaper or other abrasive method (as shown here) before assembling a ground lug to the chassis, and the bolt must be shiny and clean, with a star-washer added to bite into the chassis and prevent the ground terminal from loosening. Ideally, one should *not* use the mounting bolt for a capacitor or tube socket as a chassis ground point; better that the ground lug have its own stand-alone bolt. If there isn't a chassis hole available to use as a ground terminal, and you wish to avoid drilling a new one, just solder the wire(s) directly to the steel chassis. (If the chassis is aluminum you may have no choice but to drill a hole for a grounding lug). Note that a riveted ground point should always be assumed to be resistive, intermittent and unreliable ---- ALWAYS. Brass rivets will stretch and relax with time, heat and vibration, and the junction of dissimilar metals may cause tarnish or corrosion where you can't see it.. Many 1940s and 50's amplifiers had the riveted ground connections made AFTER the chassis was painted or anodized, and such ground points will never be long-term reliable, especially 60 or 70 years later!

Once again you teach some important lessons. I don't have any amps at this time which have a hum, but I have fixed a few thanks to you. The short piece on the reverb was interesting checking for the input and output was informative. I'm enjoying your videos as often as possible. Thanks Stuart.

@stuartukguitarampguy5830

Жыл бұрын

Always good to have your feedback thanks Michael

Hiya Stuart, it's lucky you just finished a hummer.! Nice find, shows what experience does for you. Nice fix, interesting how noisy those old amps are....Still I prefer the sound of them personally..Ed..Herts..uk..😀

I miss my old 2205 it was the bomb.

So cool, can wait until I'll bring my jcm 900 to you. Thanks

Love your work - kudos!

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Christian

You'd be surprised how well a Oscope, audio generator and dummy load work minus all the popping noises! Gotta love the bell less reverb tranny inside the chassis spewing audio into anything nearby too. Run a 1k audio signal and lower your scope probe in voltage and just move it around that transformer and watch the signal suddenly spike up. I replaced mine with a fender tank and 8 ohm bell cover transformer, problem solved.

Interesting and well done. I have the same amp and the same annoying hum. Mine is an '84 USA model that was converted to EL34's

Nicely sorted! I did the same 180 reversed mounting of the tank in my D.R. with the same resulting hum even though the tank is away down on the bottom of the combo. It was quite a bit easier to sort than that head configuration, thankfully.

@stuartukguitarampguy5830

2 жыл бұрын

Nice one, well done. Yes the head was a challenge!

When you slap the open strings on your guitar while (whilst) testing, I call it the Berkshire Blues song. Because a noisy amp gives us all the blues! Great video as always.

@stuartukguitarampguy5830

2 жыл бұрын

Ha ha! Thanks.

Bought aold MG series 100dfx with knobs and jacks with annoying crackle. So I watched your videos, cleaned the pots and jacks with electronic contact cleaner, bought new knobs and re wrapped the cabinet in ice black leather. Looks fantastic and works excellent. Thankyou sir for your tutorial

@stuartukguitarampguy5830

Жыл бұрын

Nice work. Well done!

You're very methodical. Good video.

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Zack

You have so many amps with hum issues that you should make a special series called "the hummer of the week". ;)

@stuartukguitarampguy5830

2 жыл бұрын

Yes it's been crazy this last couple of weeks. One after another!

So cool. Enjoyed this. So many amp "guru's" are bluffing or are too dramatic. Not you Cheers Brilliant!

@stuartukguitarampguy5830

Жыл бұрын

Thanks Jonathan!

Stuart, also check the resistance of the earth cable in the mains lead, they do degrade over time and could contribute to a hum problem. I had this problem with my computer psu and it took ages to find out that it was the culprit. Easy fix to swap it out to a new one. Ian

@stuartukguitarampguy5830

2 жыл бұрын

Good idea thanks Ian

Another thing that is wise to check when you think you've solved grounding problems and lowered the hum Is to play with the Variac setting and test the amplifier to the lowest and highest ranges of input voltage from the wall socket that it is likely to see. Here in the States we might see summertime brownout voltages as low as a 100 V and in some locales such as where I live the typical operating voltage is a 122 to a 124 volts. I find that if I am able to reduce the input voltage with the variac to a 100 V or a little less before the anp starts to hum again then I probably fixed the problems in such a way that they are unlikely to occur for the owner no matter what the voltages are on any given day when and where he plugs it in. This sort of a test is especially important if the device has regulated power supplies, which aren't generally seen in vintage tube amplifiers unless they have electronic or relay- operated channel or effects switching. If the tube amplifier is modern enough to have integrated circuits in it, it probably has regulated power supplies and it would be especially to important to check it at a low and high range of input voltage, both for recurrence of hum and for correct switching operation.

@T0mmyTune

6 ай бұрын

I would have tested the ground "repair" at the screw and nut before I would even consider changing the ground circuitry, ie: adding ground material. I mean, why change something that has worked well for so many years if it was simple corrosion? @ 15:19, But you will never know because you chose to alter the design vs. checking your work.

Amazing video, maybe just what I have to do. Besides the hum for which you showed the solution, now I have a constant loud buzz (which started sporadicly 2, 3 weeks ago) and the guitar sound barely comes trough. Before I was able to sort of fish the buzz out by switching full/half power switch, now it's just always in buzz mode. Turned and checked the tubes, think they are all good.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Goran, sorry but hard to help you ith that over the internet, not sure what that could be Good luck getting it sorted.

thanks for your Video, i hat the same issue whis the ground on the filter caps, i connect now all the ground-points with a wire to each other

Good job Stewart. My friend brought me his Marshall Series 2000 (same as the 2001) amp, 235 watts for a look over. This amp is two channels plus a Mix input. The Mix input jack uses a very very rare Stereo TRS (NO, NC, NC) configuration. Someone changed that out to a NC NC NC. I had to fabricate a jack but even then, the mixing is not working properly. On what I would give for a Review 1 schematic for this amp. I guess after a short run (with a Rev 2 and Rev 3 update), it was discontinued. I hope to get it up and running someday and post a final report on the web for all to see. But I will tell you all one thing.... the Series 2000 (guitar amp) and the 2001 (the bass amp) are NOTHING like the JCM line.

@stuartukguitarampguy5830

3 ай бұрын

Hi Thomas. Wow, well done for even spotting that. I';m not sure I would have. I don;t have that schematic I'm afraid. Good luck getting it worted.

Brilliant job Stu. I'd let you work on my jmp anytime.

@stuartukguitarampguy5830

5 ай бұрын

Thanks Darell

Good catch Stuart. I'm surprised Marshall didn't have a star ground near the power transformer, and another near the input jack for the f/e. Well, I suppose that kind of thing keeps you going. Cheers

@stuartukguitarampguy5830

2 жыл бұрын

Thanks Ken. They didn;t have much idea what they were doing back then tbh!

Great Stuff Young Stuart!! (Hate Hum!!)

i had this exact head in the mid 90's very dumb of me to sell it cheap . now worth alot

@stuartukguitarampguy5830

2 жыл бұрын

Yes big money these days.

Just stumbled upon your videos from across the pond. I've got a marshall 1987s reissue that I've recently changed the electrolytics in. After doing so I developed a hum as well. I wondered if i somehow created a grounding issue. I'll have to go back in now that I've got a place to start. Thanks.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Richard Just changoing the caps wouldn't introduce a gorunding issue. Sorry if this is obvious but double check your solder joints, also caps are in the right way, right??!

@richardcron2395

2 жыл бұрын

​@@stuartukguitarampguy5830 Yeah, that was my first thought as well. I had checked my solder joints and cap placement when I heard the noise after the first power up. Everything looked good. It can't hurt to check again. If I go back in there and the caps are backwards it's going to be like getting slapped in the face by Will Smith! lol. Anyhow, I was hoping for an easy fix. No such luck I guess.

This sounded like my JCM2000 which I bough brand new. I put it back to the shop I bought it from and it took 6 months to come back, I'm sure in the end they had to send it to Marshall aswell. I hope this isn't all that was wrong with it!

Re: "125 volt lamp" ---- is it a neon lamp? Perhaps they are using only half (one "leg") of the 240 V AC input, to the chassis, to get 120 volts for the lamp. I'm surprised they didn't simply use an LED run off of the heater supply.

I need to replace 3 pots in a late 80's 2205. But can't find info on their values or availability or how they're connected. Can you help?

Hi. Thanks for sharing your knowledge ! Can you just pull off a valve while the amp is on ? Does't it damage the valve ? I suppose you can't do that with the output valves (Push-pull), am I right ?

@stuartukguitarampguy5830

2 жыл бұрын

Hi, yes no problem pulling a preamp valve when on. I probably wouldn;t do a power valve just becuase pulling one will unbalance the push-pull circuit.

Excellent video Stuart ! ! Do you support the idea of wearing gloves when handling vacuum tubes ? ? Just wondering.

@stuartukguitarampguy5830

Жыл бұрын

Hi. No you don;t have to wear gloves. People are getting confused with projector bulbs which have very thin glass walls and run at extremely high temperatures.

Ho Hum. its off to work we go!

what a great tech this guy is..im new here...i like how his no fuss about the whole vintage thing. he fix,s hi fi guitar must seem so primitive ha ha.if your guitar creates hum over 6 ft from the amp ive found the transformer is normally had it. just a tip cheers

@stuartukguitarampguy5830

9 ай бұрын

Thanks Pat

@patreidcocolditzcastle632

8 ай бұрын

no problems loving the channel , your on the money because my girlfriend only lasts 2 seconds ands wonders whats wrong with me as she thinks how much ill spend to@@stuartukguitarampguy5830

@patreidcocolditzcastle632

8 ай бұрын

you would have been our secret radio guy in oflag 4c colditz pow camp.actually they built amazing radios out of bits and pieces really innovative ill subscribe and share to@@stuartukguitarampguy5830

My amp is a crate flexwVe 65 it make one pop then quiet what could it be

I just got a jvm410h and I’m getting a loud hum from the amp itself not the sound out. I’m playing the amp through a suhr reactive load and headphones so I don’t have speakers hooked up. It sounds like an old refrigerator running.

@stuartukguitarampguy5830

3 ай бұрын

DO you mean the actual physical amp is humming even without and speakers or headphones connected? Or is the sound coming through the headphones?

@JasonTheMunicipalMechanic

3 ай бұрын

@@stuartukguitarampguy5830 the physical amp is humming. It’s not coming through the headphones or the speakers. It was pretty loud yesterday but I checked it a little while ago and it was quieter today like it was the first time I used it.

@stuartukguitarampguy5830

3 ай бұрын

One of the few things that could cause that is loose bolts holding the mains tramsformer on. If you're able to get to them, give them a good tighten down and see what that does.

@JasonTheMunicipalMechanic

3 ай бұрын

@@stuartukguitarampguy5830thank you I will try that. I appreciate your help.

Normally the power supply and power tube section is grounded separate from the rest of the audio ground. I did a star grounding on my 4210.

@stuartukguitarampguy5830

Жыл бұрын

Ok that might sort it. Earthing issues are a real headache.

hello i have a 1993 peavey 5150. there is a buzzing noise everytime i connect effects units into my FX loop send and return. it’s just a constant buzz that doesn’t stop. but there is no noise when i plug the guitar into the front of the amp and have nothing in the FX loop. any ideas what it might be? i took apart the amp head and cleaned everything out with electronics cleaner.

@stuartukguitarampguy5830

Жыл бұрын

Hi no really sorry it could be so many things. I hope you manage to get it sorted.

Hi Stuart. Love your videos. Do you play guitar? I recall you said in one video that you weren't a player, but in one of your videos you do seem to play the guitar quite well. Ryan, Wilts

@stuartukguitarampguy5830

2 жыл бұрын

Hi Ryan I can hack out a tune but wouldn;t consider myself a guitarist.

@ryanrobles3501

2 жыл бұрын

@@stuartukguitarampguy5830 thanks for replaying. Keep the videos comings. I’ve learned a lot front watching you.

Liking your channel. have a question, what should a set of 6L6 be biased at for a Fender Twin Reverb ? Thank you for your help.

@stuartukguitarampguy5830

Жыл бұрын

Hi Wade. Strictly speaking it depends on plate voltage but if you went for 40mA you wouldn't be a mile off.

@wadehicks9270

Жыл бұрын

@@stuartukguitarampguy5830 thank you Sir I appreciate your help, I will test it to see what the plate voltage is thanks again.

So if the hum was in the power section, taking out the phase splitter doesn't category determine which side the issue was?

@stuartukguitarampguy5830

2 жыл бұрын

I think that's right but tbh I can't remember as it's been a while since I did the amp.

@robertogabriel6430

Жыл бұрын

It's a very good question... I want to know it too

Is this Marshall repair channel ?I am only seeing you mostly working on them

@stuartukguitarampguy5830

2 жыл бұрын

There are quite a few other amps oin the channel. It's just that Marshall are ultra common amps for people to have here in the UK.

Marshall didn't skimp on the iron

A bit of vaseline or silicon grease would have been a good idea, where you sanded the plating off the chassis, to prevent future corrosion.

@stuartukguitarampguy5830

Жыл бұрын

Good thought, thanks.

Hello from Cologne, I'm using a Marshall jcm 800 Studio. My hum Problem occurs when using the fx Loop. Any idea what that could be? Thanks in advance, Frank

@stuartukguitarampguy5830

Жыл бұрын

Hi Frank. Link out the FX send and return using a short jack-jack lead. If there is no hum it's nothing to do with the amp.

@frankhachenberg6305

Жыл бұрын

@@stuartukguitarampguy5830 good Idea. I will try.

@frankhachenberg6305

Жыл бұрын

It is the effect loop 😕

@stuartukguitarampguy5830

Жыл бұрын

@@frankhachenberg6305 So just to be clear, when you link FX SEND to FX RETURN with a jack-jack lead you get hum? If so, that's a really strange fault becuase without that lead, FX sned and return are shorted together. All you're doing with the lead is .... shorting them together!

@frankhachenberg6305

Жыл бұрын

The lead you are talking about is a patch cable, right?

Hi ..lm no repair man ,just a guitarist but personally l find just plugging in the mains socket (bang)pulling live preamp valves(bang) probably does more harm than good..Also l did not see the all important V1 valve swapped over ? Plus any guitar causes hum when you within a couple of feet from the amp..That's very basic stuff but (with respect) Most guys would know if you just alter the angle/transformers of your guitar or just back off its cured.. You guys are invaluable to us valve amp players,,l just slightly disagree with the methods to the cure..cheers.

@stuartukguitarampguy5830

2 жыл бұрын

Hi Peter. No it wasn't any of the obvious stuff, naturally I checked all that out. This was a tough hum loop internally.

Hey Stuart. What is your favorite amp to work on? If your interested in what I did before retirement look up trx lab here on youtube. Fun video as usual..

@stuartukguitarampguy5830

Жыл бұрын

Hi Monty Anything old and point to point wired I like to work on. I dislike PCB stuff, not for any purist motive but because you oftenn can;t easily change a component. I looked at your channel, you're braver man than me! My father was a very well known radio ham, G3HSR in uk and VK9NS on Norfolk ISland Australia.

@montygore1200

Жыл бұрын

Sorry Stuart. That is not me. That is Peters channel. This is just a look at what I did. Love your vids. Keep up the good work.

Howdy. Bewilders me that a brand like Marshall has not adopted the ground bus technique but insist on using the chassis as a ground conductor. Using the chassis the return currents will split all over the chassis. Some return might pass grounding points in the preamp location. Return voltage drops will add to the preamp signal. The ground bus method is not rocket science and is well known. Regards.

its 50 watt