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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
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" :-)
wolf_garcia
6,695 posts
 
I guess I should check the sockets on my 1960 Fender Deluxe…they could be an issue someday.
atmasphere's avatar
atmasphere
11,784 posts
 
A good tube socket will have tin-plated pins and will last decades as in Wolf's Fender. These days we are seeing a lot of cheap sockets with silver plated pins- they will not last very long at all. Sounds counterintuitive, but in fact tin does not want to corrode and is a lot harder than silver or gold.

Hum and tube rush are not the same thing by the way...
zd542
5,339 posts
 
"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."

Yes, but understand that definition is most likely referring to cars, and not high end audio systems. Under the hood of a car is an extreme environment for electronics and cables. The di electrics break down over time and the grease is used to "help" the aged components last longer.

Here's an actual example of what its used for: http://ww2.justanswer.com/uploads/kennyz1963/2009-11-01_144226_tsb06-09-03.pdf
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