Hi Conrad,
I experienced negative grid current once with an 8877 amp and traced it back
to a poor connection at the ground return of the HV supply. You might want
to check there first.
Hope this helps.
73
Matt
KM5VI
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Conrad PA5Y
Sent: Saturday, July 14, 2018 2:21 AM
To: amps@contesting.com
Subject: [Amps] 8877 negative grid current
Hello all.
I have a question on behalf of an Italian friend of mine.
He has 8877 amplifier for 2m and what sounds like some tired tubes. His
'normal' tube is a 3CPX1500. Recently he has noticed that when he tunes for
maximum during tuning his grid current meter goes negative. I personally
have never seen this on either of the two 8877 amplifiers that I previously
ran. He has tried 2 other tubes which do not have this behaviour although
they do produce less output than the tube that exhibits negative grid
current. So I suppose the simple question is what causes negative grid
current on high Mu triode like a 8877? Back bombardment?
73
Conrad PA5Y
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