Peavey Classic 50 Needs Your Help!

[Old Fart Rocker]

I think I know the answer, but I'll throw it out there anyway. The other day my Peavey Classic 50 2X12 started making a high pitched feedback/whine when I wasn't playing. Wasn't noticeable while I was playing, but once I stop, the sound comes back softly and gradually gets louder. A light knock on the amp or the back where the tubes are would stop the sound. My guess is I have 1 or more tubes that are microphonic. Befroe I replace the tubes I thought I would ask you guys and see if there is anything else I should check before I simply swap out tubes. Also, it was much more noticeable on the lead channel with the gain up and at higher volumes. Clean channel at lower volumes, I didn't hear it.

Any and all opinions are greatly appreciated!

[WRGKMC]

Yes, it sounds like your classic has a classic case of preamp tube microphonics. This usually happen with cheap budget tubes or someone sticking Hi Fi grade tubes in there.

Back in the day, they made 7025 tubes whick were supposed to be an industrial version of the 12AX7 preamp tubes. They also made 6L6GC tubes and the GC stood for industrial grade. Its not so much the quality as the ruggedness of the tubes. Amps get moved around and combos vibrate the elements loose. 

They used to make military grase tubes encased in metal but I havent seen many of them around in a long time like when I was growing up. There was allot of army surplus around and those tubes were dam near bullet proof.

Sovetec makes some extra heavy duty tunes that have thicker Mica separators that hold the elements in place. There a few others that can take the pounding like JJ's which are pretty solid. The rest are a mixed bag for durability. Luckily tubes are cheap and its an easy fix to plug in new tubes. If you do get power tubes make sure they are a matched pair. I'm not sure if that amp is self biasing so you'll need to incvestigate tht.

To prevent microphonics in the future and sustain tube life you may want to try thes Tube Dampeners (kock rings)  I stumbled over them today and they may work well to abdorb vibration and extend a tubes life from rattleing appart. They wont help the tubes that are in there now. They are definately ready for the trash bin, but they should help prevent premature conception failure.  

http://www.thetubestore.com/Parts-Accessories/Duende-Criatura-Tube-Rings

 

[Old Fart Rocker]

Thanks for the input! I have JJ's in there now, but the tubes are 3 years old. I do 50 gigs per year plus rehearsals and fill in stuff. I'm sure I'm due for the ol' retube.