Recapping a Silver Panel 1971 Super Reverb

[Pacreamer]

Hey All,

Quick background. Amp repair beginner here. But I've got experience soldering and building my own pedals and working on other audio electronics.

I've been doing a ton of research on recapping my Super Reverb. Both in terms of safety and the process/components for the job at hand. I think I have a fairly good idea of what my process will be.

1. Verify the amp is unplugged.
2. Remove chassis from cabinet.
3. Measure DC voltage of caps in the doghouse.
4. Discharge caps in doghouse.
5. Verify the circuit. (not printed on tube chart)
6. Replace and install new caps.

I've also considered getting one of these from Stewmac to aid me in discharging capacitors. What do you think?
SnufferStick

Just a couple questions:
1. Do you have any cap recommendations that you like?
2. While I'm in the amp, should I inspect anything else? Anything easy enough for a beginner to check and replace?
3. Any other safety tips/advice for me? I'm well aware the voltages in tube amps can kill. Want to make sure this process is safe.


I'll post some pics of my process here.

[i love sharin foo]

I used to use Sprague Atoms and F&T caps a lot but they’ve gotten really expensive. I still use them in smaller values and lower voltages where they’re cheaper. I now use the MOD brand that Antique Electronics has a good bit. They’re affordable and have held up fine so far.

I always adjust lead dress slightly where I can in my old Fenders. Nothing major, but you can probably improve it a bit with little effort. I like to take a good look at the chassis grounds. I’ve had a failure or two before so I try to reflow them here and there for extra protection. They will require a big iron though. If it doesn’t have a grounded cord, you could do that too. If you have any loose tube sockets, you may be able to retension them while it’s apart.

I mentally go through a check list before I touch anything inside. I hold the unplugged power cord in my hand. And make sure I meter at different points. Whenever I am inside while an amp is running, I close the door and make sure no one is in the room. No pets either. And I put my phone somewhere else. And while running, I keep my left hand in a pocket or behind my back.

I’m not a professional or anything but I have built a few amps and repaired/ modified/ recapped a bunch more.

[JSett]

I concur with Justin. Those are simple easy measures to lessen the chance of zapping yourself.

I use F&Ts for all the big caps and Sprague's for the smaller ones. They have gone up a bit in price but I think it's worth it if it's an amp you intend to keep for a long time or is worth a bit of money. And if you can afford the extra $20-30 of course. For can capacitors I have used JJs before (along with others) and they've been fine.

I have one of those cheap little led discharge units that tell you that the current is gone. Then I check with a multimeter to be sure. There's always a slight hesitation putting the hands in for the first time though oh, and use a wooden chopstick to poke around in if you need to while there's current stored or flowing.

The cap dischargers are easily available on eBay for cheap enough, just make sure you get one that's 800-1000v as some amps caps can be pretty high. They usually look like this...



Good luck and be safe

[GreenKnee]

From my days in industrial electrical maintenance I have continued to wear tight, nitrile gloves when carrying out electrical work on anything. It's just an extra later of protection in case of inadvertently touching the wrong thing.
Had one 240V shock when I was an apprentice, and not had one since. Learnt the hard way

[JSett]

From my days in industrial electrical maintenance I have continued to wear tight, nitrile gloves when carrying out electrical work on anything. It's just an extra later of protection in case of inadvertently touching the wrong thing.
Had one 240V shock when I was an apprentice, and not had one since. Learnt the hard way

I didn't even think about that. I have an endless supply of nitrile gloves at work. The most I ever had was about 740v into a wrist... That hit home for sure and I've been mega extra super duper ultra careful since

[Pacreamer]

Thanks for all the helpful replies, everyone. I really appreciate the ideas and advice.

I'll hopefully be cracking into the amp today - at least taking the chassis out of the box. I'll update with photos for circuit ID.

[øøøøøøø]

Don’t forget the bias filter cap

It’s just as important as the rest. It’s located on the little board near the pilot lamp assembly

DO note that this bias filter cap is connected the “wrong way round”—its positive lead connects to ground, as the bias supply is a negative supply. Just take photos and copy the orientation of the original part

You should be able to up-rate this cap a bit… going a bit higher on capacitance and considerably higher on rated voltage is advised.

For the rest, the easy way is to use F&T for guitar amps but if you want to get into detail, brand is less important than what’s on the datasheet.

Uprating the cap for temperature and/or voltage is completely sensible. I like to “fill up all the space”—go higher on temp, lifespan, etc until I get a cap the same physical size as the OEM part. But that’s a bit of work, and just using one of the common “amp repair tech” brands like F&T is just fine.

A visual inspection of the resistors in the power supply is a good idea. If there’s any evidence that they’ve been getting hot, replace them and up-rate for power handling.

If your amp is still configured as bias-balance and hasn’t been converted to the black panel-style bias adjust, now is also a good time to do that

Go ahead and bias your output tubes while you’ve got it open. If you need help/info, just search or ask. In a SR, i like to shoot for 60% max dissipation (about 40mA per tube)