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DeVille 212 amp trouble. [message #9644] Sat, 22 April 2006 19:09 Go to next message
James is currently offline  James
Messages: 23
Registered: May 2009
Chancellor
Help

Blowing one of the 6L6's after short use. Bias trouble?
thanks JIM

Re: DeVille 212 amp trouble. [message #9645 is a reply to message #9644] Sun, 23 April 2006 02:18 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
It`s hard to say - see the answer to the similar message. You can try to measure all the voltages on tube sockets, even without opening the cover. If you don`t know how to mesure HV safely and check the bias - maybe trip to the tech is in order?

Re: DeVille 212 amp trouble. [message #9646 is a reply to message #9645] Sun, 23 April 2006 16:28 Go to previous messageGo to next message
James is currently offline  James
Messages: 23
Registered: May 2009
Chancellor
Hey thanks for your quick reply.

I checked all the pin voltages on both 6L6's with the tubes pulled.
They are as directed. Got nice heater volts, 500v B+, and -50v bias on the grid. I'm lost. Short of simply changing out the electrolitic caps, I'm looking for a techy guy to take over!
Thanks again JAMES

Re: DeVille 212 amp trouble. [message #9647 is a reply to message #9646] Mon, 24 April 2006 07:36 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
If all those voltages are OK, then chances are that you`ve just had the bad tube. Try another good tubes, but look to the plates - if they turn red, switch it off immediately!
(The proper metod, of course, would be monitoring cathode current through small R=10 Ohms between cathode and the ground - 30...40mA of standing current.)

Re: DeVille 212 amp trouble. [message #9648 is a reply to message #9647] Mon, 24 April 2006 15:59 Go to previous messageGo to next message
James is currently offline  James
Messages: 23
Registered: May 2009
Chancellor
Well, this might be my lucky day. With all the voltages okay, I used a trouble light and magnifying glass and found some cold solder joints where the tube socket meets the PC board. A few minutes later, bingo! I THINK the trouble has been resolved. Can tell more later. Again thanks for all the tips and ideas...JAMES

Re: DeVille 212 amp trouble. [message #9649 is a reply to message #9648] Tue, 25 April 2006 06:07 Go to previous message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
With absent negative "bias" voltage on g1 (pin 5), the tube "draws" large current and quickly overheats. PCB traces can be "intermitent" `cos of heat, vibrations and by pushing tubes in the sockets. Clean burned carbon marks (conductive) on the tube socket, if old tubes remained any. Good luck!

"That`s one small step for a man, one giant leap for manikin."

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