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Tube Amp Maintenance Tip...

Interesting maintenance tip story.....My C-J LP66S amp has been creating a 'variable volume sign wave' type hum in my speakers lately. The hum did not go away with warm up. I pulled the 4 power tubes and 3 signal tubes out of their sockets. I blew out each socket and pin with Can-O-Air. I also pulled the two fuses & blew out the holders /holes. Then I applied a very thin coating of Di-electric grease to each tube pin hole. Finally, I crossed the 4 power tubes (6550) left to right and just rotated one position each of the three signal tubes. Performed a re-bias once the amp powered up. No new parts involved, let's just call it a 'dusting & cleaning'. Long story short, issue resolved. Not sure what I did to correct the noise or why it even started. Perhaps a mote of dust in the wrong place? Moral: If your having some noise issues with your tube equipment perform some basic cleaning procedures prior to going into any type of panic mode. Hope this helps someone in the future!
quincy
atmasphere's avatar
atmasphere
11,784 posts
 
You really want to be careful about treating tube sockets with chemicals! If the chemical uses any sort of oil base the socket can be contaminated and problems (perhaps failure of the tube and requiring replacement of the socket) can ensue.

For this reason I use spray 'contact cleaner with silicone' such as Radio Shack used to sell. That's about as active as you want when cleaning tube sockets!!
quincy OP
350 posts
 
Excellent feed back....Thanks! Looks like I'll be spending the evening with some cotton swabs and some Acetone solvent cleaning pins and sockets. May try some Freon Brake Cleaner as well.

All that I am currently experiencing is a very soft hum from the amp through each speaker pair and through each speaker (low, mid, high ) . I believe this is normal tube rush? Can't hear any hum with music playing. Any thoughts on that issue? (Amp always had a bit of hum from the factory, but that does not make it OK.)
zd542
5,339 posts
 
"All that I am currently experiencing is a very soft hum from the amp through each speaker pair and through each speaker (low, mid, high ) ."

When you go to the auto parts store to pick up the brake clean, get a can of penetrating oil and lube the moving parts in the amp. If the hum goes away, take it apart and use something more permanent like wheel bearing grease or anti seize.
quincy OP
350 posts
 
"When you go to the auto parts store to pick up the brake clean, get a can of penetrating oil and lube the moving parts in the amp. If the hum goes away, take it apart and use something more permanent like wheel bearing grease or anti seize." Zd542

Ouch! That hurt Zd542! Contact cleaner it will be!

Dielectric grease:
Dielectric grease is electrically insulating and does not break down when high voltage is applied. It is often applied to electrical connectors, particularly those containing rubber gaskets, as a means of lubricating and sealing rubber portions of the connector without arcing.
marco1's avatar
marco1
518 posts
 
Give you one better than that. I've always had a hum coming through the Premier 15 (phono) into my Premier 16 and Premier 12's. Suffice it to say I tried everything to get rid of it. BTW, I have 4 dedicated circuits. Recently I replace the floor in my listening room. I had to breakdown and move all my equipment to do so. It's now back in service, wired identical to the way it was before, and the hum is gone. I guess "a few inches can matter" :-)
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