I've seen negative grid current on Drake amps when one of the filament
bypass capacitors is leaky
Paul K0UYA
-----Original Message-----
From: Stan Gammons
Sent: Tuesday, November 07, 2017 9:53 PM
To: amps@contesting.com
Subject: Re: [Amps] Problem with my Henry 2K-4A
Every time I've seen negative grid current it was due to a shorted
tube. You might try taking one of the tubes out and seeing if you can
isolate it to a single tube. I don't know what experience you have
working on amps, but just be aware there is lethal voltage in the amp.
Please exercise caution working on it.
73
Stan
KM4HQE
On 11/07/2017 06:52 PM, Mark Beckwith wrote:
Greetings,
I'm writing the [Amps] reflector in hopes that someone reading will be
able to diagnose my problem with confidence. It seems like the Henry
2K-4A is a pretty well-known amp. I imagine the answer is here somewhere!
Lately when I transmit, after a couple minutes, I hear a very quiet
"click" and the plate current swings positive by a little (150-300ma or
so, depending on whether the plate voltage switch is in "CW" or "SSB"),
the grid current goes negative, and the amp no longer transmits. If I
leave it like this for a little while longer, the built in circuit breaker
trips.
Initially, the circuit breaker would not trip, I would hear the tiny
"click" again and the unit would be restored to operation for a little
while longer, before failing again. After an hour or so of this, it
stopped correcting itself and would only blow the breaker.
If the amp was turned off and left to cool for a while, it would go back
to operating, but only for a few minutes until it failed again.
This happened the same regardless of the position of the bandswitch.
Now after a couple days of this, it seems to be permanently in the failed
mode.
Does this sound familiar to anyone?
Thanks in advance,
73 - Mark, N5OT
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