? It never ceases to amaze me how often amplifier experts seemingly do
not read manufacturer's specification sheets. To estimate
grid-dissipation, multiply indicated grid-current by the RMS voltage at
the cathode. As I recall, the RMS potential at the cathode of a 3cx800A7
is c. 50V. Thus, 40mA of grid-I = c. 2 watts dissipation on the 5W-rated
grid.
cheerz, Eric
>Interesting, Commander wants you to keep it under 40 ma and it has a
>protection circuit that trips just over 40 ma.
>
>
>----- Original Message -----
>From: "R. Measures" <r@somis.org>
>To: "ERIC OLSON" <ericn7epd@msn.com>; " AMPS" <amps@contesting.com>
>Sent: Sunday, March 14, 2004 8:34 PM
>Subject: Re: [Amps] Commander II output circuit
>
>
>
>
>>Hello! I just purchased a used Commander II 2 meter amp and it runs high
>>grid current all the time. About 30 ma at 10 watts drive and 40 ma at 20
>>watts drive. I swapped the 3cx800 with a "good one" from a friend and it
>>does the same thing. Checked for shorts and ground connections in the
>>final
>>compartment but all OK. Replaced the DC blocking doorknob cap and no
>>change. The link coupling is very rigid and I doubt it would change much
>>from amp to amp or in transport. Get about 450 watts out at 20 watts drive
>>and 250 watts out for 10 w drive so think the tube is OK. Help!
>
> 30mA represents c. half of the rated grid dissipation.
>
>cheers, Eric
>
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