changing capacitors in Blackface Super Reverb

[staffhog]

I have a '64 Fender Super Reverb. I want to change out the capacitors to see if that restores power and undistorted sound. Is there anything to do other than removing the old capacitors and resoldering the exact replacements in their place??

[Kap'n]

Is there anything to do other than removing the old capacitors and resoldering the exact replacements in their place??

1. Observe all electrical safety rules, especially the one about draining the filter caps.
2. In general, only replace the electrolytic filter caps. Those are the ones under the 'doghouse' on the bottom of the chassis, the one on the small bias supply board, and a handful of small ones on the main board. Don't replace any of the blue molded caps with the white labels!
3. Make sure you observe the correct polarity on the filter caps. One of the caps under the doghouse is'upside-down' compared to the others.

[staffhog]

K'apn: First, thanks for the reply and the sharing of the knowlege. I am unfamliar with some of your references. I have removed the rectanglular"doghouse" on the underside of the amp to expose the capacitors, 2 big ones: 53D, 68UF, F 85 on one side / 450DC on the other. These are facing different directions so I assume this is the reverse polarity you speak of. Then there are 3 smaller ones:22, 500, +-20% on one side=/ 85* on the other. Does this sound right ?? These were replaced only once and I observed but didn't realize I would move away from the guy I trusted to do the work therefore I didn't pay close attention to detail. The "draining you mention is greek to me, can you explain?

[Kap'n]

Yes, that sounds right (capacitor orientation).


There are some FAQ's on the web on how to discharge and replace caps. The big dangers are

1. making sure the amp is unplugged ( ) and
2. the filter caps have had their charge drained. They store energy, and if you touch the hot side, a necessity when chanigng them, you can get shocked.

Essentially you need to jumper from the hot side to chassis ground. Some folks like to use a resistor to limit the current, and it's probably a good idea, even though I never do it. Usually I'll hook a clip lead to the plate or screen of one of the power tubes, and short the other end to the chassis.

However, if you're unfamiliar enough to need to look up the terms, you should have somebody help you out the first time. Or at least read through some more comprehensive descriptions.

[DoobieK]

I recommend keeping the jumper on the lead while doing the work, or letting the caps drain overnight. You can get a reading of a couple volts, but when you remove the jumper, a lot of the voltage might reappear. Not a good thing. Make sure the caps are drained and stay drained.

[Kap'n]

I recommend keeping the jumper on the lead while doing the work, or letting the caps drain overnight. You can get a reading of a couple volts, but when you remove the jumper, a lot of the voltage might reappear. Not a good thing. Make sure the caps are drained and stay drained.

Don't forget to remove it before powering up.

[DoobieK]

Don't forget to remove it before powering up.

Speaking from experience?

Seriously, a cap job on any PTP amp is pretty easy, safe and cheap. You just have to be very careful about draining the caps and making sure the new electrolytic caps are mounted with the polarity correct. I Have re-capped my Allen Old Flame a couple times, trying different caps to see which type I like better. I have an electronics degree, but still get a little thrill each time I repair or mod an amp and it works!

[Kap'n]

Speaking from experience?

Yes. You blow the fuse the second you flip the standby switch.