[AMPS] Trouble shooting 8877 amp

[Steve Bookout]

Hello everyone,

The other day I (we) were trying to get my home brew 8877 HF amp fixed in
time for the CQWW CW contest, but ran into a dead end.  I thought maybe
someone here could point me in the right direction and give me an idea
where to look.

Several months ago the amp when 'bang' while running on 40 meters.
(Actually, it went 'FWOOOOP!!' since I did have a 20 ohm surge resistor in
the B+; controlled 'bang'.)  The culprit was traced to be a Millen HV
connector which arced thru at 4kv.  (I know the tendancy for these
connectors to absorb moisture has been discussed here.)  The surge resistor
was blown apart as expected.  Replace both pieces  With the amp off using
external low voltage pwr supply, the grid trip circuit was adjusted for 75
mils and the grid current meter was calibrated.

When fired up and keyed, the amp draws no plate current, and at the
slightest hint of RF the grid current climbs and quickly trips out.  Our
first thought was the HV had gone away, but it is still there.  I didn't
see it, but was told there is a slight twitch or rise in the plate current
as the grid shoots up.

Knowing the grid trip was working, I stuck my spare tube in and got the
same results.

Any ideas would be appreciated.

73 de Steve, NR4M



---------------------------------------------
Steve Bookout, NR4M (ex NJ4F)
Rapidan Data Systems

'DX4WIN...The way logging programs should be!'
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