Sunn 200S

[gbono]

Hello,

I have replaced the filter caps in the power supply in this amplifier several years ago. Now it appears that I'm getting some sort of modulation (60/120Hz) mixing into the input signal. I have to assume that a bypass cap is the issue. Any suggestions regarding this problem??

thx

[Enzo]

Bypass cap?

Actually, the best clue you can provide is whether it is 60 or 120Hz. Each comes from a different source for hte most part.

Some thoughts:
1. Just because you replaced the filter caps a while back, doesn't mean one didn't fail, or the solder that connects it failed.

2. Bypass caps will not introduce hum, they will affect frequncy response and gain.

3. Isolate the problem. Is the hum present without signal? Is it present with all the controls set at zero? DO any of the contros affect the amount or tone of the hum?

4. Have you recently replaced the phase splitter tube? If so is it a Sovtek?

5. You might have replaced all the B+ filters, but did you replace the bias supply caps as well?

6. Are all the jacks tight and making good contact?

7. ANy loose nuts on the pots?

8. Any loose hardware on the transformers?

[Amp Kat]

I agree and check your reverb connections and the pan as thats a good suspect for hum in these. I think that splitter tube is the 6AN8 or is it 7199 for that model ? Try pulling that tube and see what happens.

[gbono]

Thanks for the replies. The issue is hum per se but IMD. The amplifier appears to be "mixing" 60/120Hz into the signal path. Very noticable when playing the "G" string on a guitar. I'm assuming a bypass cap has failed after +30 years.

THX

[Amp Kat]

Just for kicks I'd replace all of the caps and I did a Solarus and went from the 6AN8 to the 7199 ( wire changes) and pulled all of the can caps out and installed radials on a terminal strip inside the chassis. Changed it over from KT-88's to 6V6's as there really wasn't a working component or transformer in this amp when I got it. Can't tell you what the new caps did for this amp much less the other changes so it is well worth every bit of change for the better with these as they sound awesome. I tried to buy the Solarus from the guy but after he heard it he wouldn't have any part of it. The only negative is that power switch is extremely hard to find and the switches nowadays aren't any where near that size or type but other than that there great amps.