[AMPS] PA-77 question, round two

[Phil Clements]

>>>Eimac rates the 8877 at 20w max. grid dissipation.  Normal grid/cathode
>>>potential is 55Vrms.  With 75mA of grid current, dissipation is approx.
>>>4.1w.
>>>
>>>Why do you limit grid current to 75mA, Phil?
>>>
>>>-  Rich
What would you limit the Ig to on your amp, Rich?
Apparently, you think 75 ma is too low, although the tube is maxed out
at 60-65 ma.  Limiting the Ig to 75 ma allows the tube to operate at its
maximum power output. Would you put a 30 amp circuit breaker on a
circuit in your home that is only rated for 15a?


 I am in the business of having
>>to buy tubes. Prices are soaring, as I am sure you know.
>>
>>Why push your luck on a very fragile grid
>
> I have a dissassembled 8877 in front of me.  The grid is composed over
>of slightly over 100 gold-plated molybdeum bars   Elevating such a grid
>to a high enough temperature to boil gold would require considerable
>energy.
>>When lightly loaded, by mis-tuning or wrong antenna, the 8877 Ig soars more
>>rapidly than any other tube I have used. Alpha 77 series owners will certainly
>>agree with this!
>>
>Alpha 77s do not have a truthful grid-current meter.
>
I was not referring to meter accuracy, Rich. You are correct; the Alpha Ig
meters are off by 100%. I was referring to the rate of change when the
loading cap is moved about.

The toughness of the grid on the 8877 is a relative term. Comparing it to
the grid of a 4-1000A, which a lot of us cut our teeth on, it is fragile.

(((73)))
Phil, K5PC




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