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!

Showing 4 responses by zd542

Why put dielectric grease on the pin holes? It seems like that would do more harm than good.
"10-25-15: Quincy
Yes, I had some reservations in regards to the di-electric grease, but it is a good conductor and used on very sensitive electrical connections in automobiles. (connectors on oxygen sensors for one example)."

You have it backwards. di-electric grease is not a conductor, its a di-electric. That's why they call it di-electric grease in the first place.

Cars are a different application. Its used as a sealant . As a car ages, things like plastic connectors and harnesses deteriorate and loose the ability to fully insulate electricity. And when that happens you get arching that can do a lot of damage. Think of it as wrapping an exposed conductor in a piece of wire with electrical tape, so it won't make contact with metals that conduct electricity.
"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.
"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: