Anyone Ever Change The Caps In Your Amp?

[dfrattaroli]

I found a highly reputable tech in my area and am considering having him change the caps in my Marshall. The more I read about it though, I feel like taking a shot at it myself. I've built a guitar from scratch, cabinets, made cables, wired up pickups, etc. I'm also confident I can work safely in this amp. It has bleeder resistors and I know how to read the voltage that may be stored. I also know how to drain the caps if need be.

Just wondering if anyone else has done it. I have had a long standing desire to work on amps and learn how to mod so here I am.

Dave

 

[FourT6and2]

Are you talking about the filter caps? Then yes, it's very easy. Especially in most Marshalls.

Before you start, drain the caps, and attach a bleeder wire from V1 to the chassis (keep your hands OUT while doing this). Let the caps drain. And then keep that wire there while you work in the amp.

Then sketch out on a piece of paper what wires attach to which pole of each cap so you don't lose track.

From there, it's pretty easy. The cap(s) under the board should have enough lead on them to do the soldering from the top of the amp without having to lift the board. The others are self-explanatory.

I can walk you through it if you want.

If it's a PCB amp, then it might be slightly different. But still easy. Depends on if the caps are attached to the PCB or with flying leads.

 

[dfrattaroli]

Are you talking about the filter caps? Then yes, it's very easy. Especially in most Marshalls.

All of them. The main HT caps, DC filament, reverb board... There's a shit load of them though. I counted about 30. The most daunting part appears to be the partial dis-assembly of the boards. The amp is 16 years old and the tech said they most likely need to be changed. I've been inside and took pics. None of them look bloated at all but I understand that's not always the case.

 

[dfrattaroli]

sounds like you have SOME experience. maybe shadow your tech over his shoulder while he does it this first time

I've thought of that too. He said it would be a 2 hour job. Just don't know if he's cool with customers watching or if he'll do it while I'm there. I may ask him though.

 

[FourT6and2]

Are you talking about the filter caps? Then yes, it's very easy. Especially in most Marshalls.

All of them. The main HT caps, DC filament, reverb board... There's a shit load of them though. I counted about 30. The most daunting part appears to be the partial dis-assembly of the boards. The amp is 16 years old and the tech said they most likely need to be changed. I've been inside and took pics. None of them look bloated at all but I understand that's not always the case.

30?!

lol I think you're going overboard on this. Do people typically replace ALL of the electrolytic caps in an amp or just the filter caps?

Sounds like the amp is PCB? Which model are you specifically talking about?

 

[dfrattaroli]

Are you talking about the filter caps? Then yes, it's very easy. Especially in most Marshalls.

All of them. The main HT caps, DC filament, reverb board... There's a shit load of them though. I counted about 30. The most daunting part appears to be the partial dis-assembly of the boards. The amp is 16 years old and the tech said they most likely need to be changed. I've been inside and took pics. None of them look bloated at all but I understand that's not always the case.

30?!

lol I think you're going overboard on this. Do people typically replace ALL of the electrolytic caps in an amp or just the filter caps?

Sounds like the amp is PCB? Which model are you specifically talking about?

This is the JCM 2000 DSL. Separate PCB for reverb, preamp, power. I assume he meant all of them because he said it would be wise to do a "full cap job". Turns out, he has documented the process on the very same amp on one of the web sites and he in fact showed all the old caps he pulled out. I counted over 25.

 

[FourT6and2]

Well... I say go for it.

Working on PCB is going to be a little more difficult though.

Is the PCB double-sided? I mean are they plated thru-holes? If not, you'll have to lift the board to de-solder and re-solder. And that means disconnecting a lot of connections. But if the PCBs are thru-plated then you can de-solder and re-solder from the top, without lifting the board, which makes it easy.

 

[dfrattaroli]

Well... I say go for it.

Working on PCB is going to be a little more difficult though.

Is the PCB double-sided? I mean are they plated thru-holes? If not, you'll have to lift the board to de-solder and re-solder. And that means disconnecting a lot of connections. But if the PCBs are thru-plated then you can de-solder and re-solder from the top, without lifting the board, which makes it easy.

Unfortunately, they don't look thru-plated. From the top for example, I can see the legs of a resistor just "disappear" into their respective holes but no solder is visible from the top. I assume it all has to be solder from underneath.

Let's put it this way, I know I have the ability to do it. My main concerns are: 1) Draining all voltage and making sure it stays that way while I work. Even though I "know" how to do it, I've never done it. I'd literally sweat the whole time. 2) I don't look forward to pulling everything apart. I know I'll have to label the shit out of everything so it all goes back together.

I like the idea of watching him do it one time. But the whole time I'll be thinking "I could have save so much money by doing it myself".

 

[midnightlaundry]

I had a Filter Cap short to ground and it took my Choke with it on my old 2:90 power amp.. After like 8 years(?).. Sprague Atoms..

Anyhoo, I did it with a shitty iron with a dull ass tip long before I understood how an amp works.. YOu can see it on this pic.. I have a nice one now btw..

If you have any mechanical skills, it can be done. You only really learn by doing.

Before

After

 

[tubortski]

I'm curious to know if the amp still sounds good at age 16? Might be cool to document sounds before and after?! Seems like the motivation to get em done is the age and the recommendation of your tech?

 

[Loudness250]

Usually when doing a cap job, it's usually just the main big power supply caps that get changed, I've done those many times but not every cap in the amp. Just make sure there is no stored voltage in the circuit. If you turn the standby off and unplug the amp the caps will drain. wait overnight and then test the caps with a meter the next day, the voltages should be pretty much down to nothing by then. After that, change as many caps as you want, it tedious but not that difficult.

 

[dfrattaroli]

I'm curious to know if the amp still sounds good at age 16? Might be cool to document sounds before and after?! Seems like the motivation to get em done is the age and the recommendation of your tech?

Amp sounds fine to me. The only issue I have with it is an intermittent static sound that comes and goes. Happens on both channels and I'm pretty sure it's in the preamp. And yes, it was one of the first things the tech said to me on the phone. The amp is 16 years old so he said that was the first thing to do.

 

[JerryP]

Your caps don't need to be changed yet. Save your money.

 

[dfrattaroli]

Your caps don't need to be changed yet. Save your money.

Interesting. I do need to trouble-shoot the intermittent staticy, kind of in between radio station sound I hear. It comes and goes.

 

[reverymike]

Unless the caps are bulging or there's an obvious problem, chances are the caps don't need to be replaced.

I have a '71 and '78 still with the original caps. Both amps sound great.

 

[Racerxrated]

Your caps don't need to be changed yet. Save your money.

Interesting. I do need to trouble-shoot the intermittent staticy, kind of in between radio station sound I hear. It comes and goes.

Had the same sound in my 2204. Pulled the preamp/power tubes and cleaned the sockets, sound went away. Also had a 79 JMP, sounded great..got the caps changed and it didn't sound any different. My 82 sounds great, original caps. I'm leaving it alone.

 

[FourT6and2]

That noise sounds like a preamp tube problem. Probably microphonic. Or just random EMI/RF interference. Does the amp make that noise without an instrument cable plugged in? Turn he volumes up but without a guitar plugged in. If it makes that sound, it's probably a tube issue.

 

[dfrattaroli]

That noise sounds like a preamp tube problem. Probably microphonic. Or just random EMI/RF interference. Does the amp make that noise without an instrument cable plugged in? Turn he volumes up but without a guitar plugged in. If it makes that sound, it's probably a tube issue.

I've changed all the preamp tubes. Have a quartet of JJs in it now. It didn't solve the issue. I don't have any extra power tubes to try at this point. Looks like a relatively fresh set of JJ labeled Ruby EL34s. But I did pull all the tubes and put some Pro Gold Deoxit on the pins and then put them in and pulled them out a few times. Still no joy. The noise still happens with nothing plugged in and the volume on zero.

 

[Racerxrated]

Maybe clean the effects loop inserts? Spray some of that cleaner you have and push a cable in/out? I know that's worked with older Jubilee/2205s I've had with some sound cutting in/out or volume reduction..also static.

 

[dfrattaroli]

Maybe clean the effects loop inserts? Spray some of that cleaner you have and push a cable in/out? I know that's worked with older Jubilee/2205s I've had with some sound cutting in/out or volume reduction..also static.

Tried that too. However, I have the liquid form of Pro Gold. Maybe a spray would be better.