[AMRadio] 6BE6


Donald Chester k4kyv at hotmail.com
Thu Jun 24 12:06:37 EDT 2004



>Running tubes to hard will cause them to fail, excessive plate voltage,
>screen voltage, plate current.
>Cathode resistors going low, shorted/leaky cathode bypass caps?
>...Collins used to advertise they ran the 75s series at 150 volts to reduce
>heat and
>extend the life of the tubes...
>
>Maybe run a test, and see just what the tubes are running at voltage and
>current wise...

I had the same problem with 6V6's in my receiver's outboard audio amp.  It 
is a modified 50's vintage 10w hi-fi amplifier that uses a pair in the 
output stage.  I would put in a new set of tubes that checked good, and 
after a few months I would recheck them and they would test weak.  A couple 
of times the audio level actually dropped because the tubes had become so 
weak.  All tube voltages and currents measured well within the ratings 
recommended in the RCA tube manual, but I tried reducing the screen voltage, 
increasing cathode  resistance, and put the whole amp on a variac and 
reduced the a.c. voltage to 110v going into the amp.  So far the latest pair 
of 6V6's has held up.

-k4kyv

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