>
>Greetings,
>
>I had an odd thing happen with my AL811H (four 811As - Grounded Grid) this
>afternoon. When I turned on the main power switch I heard a loud pop and
>saw a flash. After that the amp had normal high voltage but would only
>produce low power with higher VSWR. After taking it apart, I discovered
>that three of the resistors that run from the grid to ground had "blown"
>apart. I can easily replace the resistors, but would like to know what
>caused it.
The grid resistors were very probably not faulty. Too much grid current
likely blew them. Intermittent parasitic oscillations produce bursts of
high grid current. . What is the resistance of the anode
parasitic-suppressor resistor in the tubes that blew their grid resistors?
>I can find any other burned parts and everything seems "normal"
>(except the low power). I noted that two of the tubes (Svetlana 811As) have
>slightly deformed plates--but a quick check with a VOM does not show a
>short.
To see what's what with tubes, you need a high-pot.
>
cheers, Tom
- Rich..., 805.386.3734, www.vcnet.com/measures.
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|