'68 Super Reverb slight buzz on note decay help.

[Doc Simons]

Hope I can get some help. On my'68 drip edge Super: Amp is strong, loud, totally tone worthy. Problem is: as a chord decays, there is a slight fuzzyness. It will often go away as the notes continue to decay. Sometimes it happens on the attack side, but mostly on the decay. All the caps have replaced at some point, mostly with Mallory 150's and Sprague Atoms in the power section. Tubes all good. Voltages all test right. It's not the speakers-does the same thing through other speakers.

[beasleybodyshop]

Does this amp have its original 100K plate resistors? Check those. Do you also have the bacon frying sounds as well? Fuzzy decay sounds like a leaky coupling cap.

[Doc Simons]

I will check the plate resistors. Any particular coupling caps to suspect? I guess I can go through subbing out each one. By "bacon frying sound" do you mean what's also referred to as "snap crackle pop" from plate load or other failing resistors?

[xtian]

Does it make this sound only at higher volume, or also at low volume?

[beasleybodyshop]

I will check the plate resistors. Any particular coupling caps to suspect? I guess I can go through subbing out each one. By "bacon frying sound" do you mean what's also referred to as "snap crackle pop" from plate load or other failing resistors?

Are you sure the tubes are good? Swapped in good known tubes?

Yes, i call it the "bacon frying sound". Its an issue with carbon comp plate resistors. I swapped out all the 100Ks in my '70 blackfaced SR with 2w high tolerance metal films. It was probably a bit overkill but hey no more snap crackle pop

[Doc Simons]

2W? That is overkill, but if it works-do it! I don't use carbon comp. resisters, but I will make sure they've been replaced. I don't get why the Vintage Police are all about them. Some old things are better, but some not so much.

[Firestorm]

Problem equal on both channels?

[Doc Simons]

Good question. I will check when I get home.

[Doc Simons]

Xtian: seems worse with volume, but sometimes on low volume. Weird thing, at low volume the buzz starts sooner.

[Doc Simons]

Firestorm: What would be the significance of one vs. both channels?

[Leo_Gnardo]

Possible crossover distortion in the power amp due to insufficient bias current.

Another thing to look at is corrosion on preamp tube pins.

And the usual search of the board, tube, ground and control wiring for broken solder connexions.

[Stevem]

I have seen this happen from 4 things, a bad preamp tube, a bad speaker,
Cold bias as was posted and poor conections in preamp tube sockets.
If both channels are doing it than you can rule out the two first preamp tubes as viewed from the right rear and move on to the other preamp tubes and other checks.

[Doc Simons]

Thanks to all. Turns out it was the speaker(s).

[Stevem]

Let me guess, the speakers are CTS brand and the EIA code stamped on them starts with 137?

[Doc Simons]

Good guess, but I wasn't paying thru them. Was using a cab with old Celestions. I recently had those original CTS's reconed. They're AlNiCo and sound very sweet, though not real efficient. But who needs efficiant with a Super? Going to double check tonight before I put it all back together.