[Amps] Henry 3K trouble

[A.R.S. - W5AMI]

Hello,

I have a Henry 3K Classic (8877) which developed a problem a couple days ago.

I'm hoping some long time Henry types (or anyone else) might steer me
in the right direction.

First, there was an arc over between the chassis and the bottom of the
plate choke where the HV connects.  This caused R106 in the HV supply
to blow.  I had spare 25 ohm 25 watt wire wounds and replaced R106.

The HV came back after replacing the resistor, however now my grid
current goes way high.  Even keying the amp with no audio on SSB shows
about 15 to 20 mils of grid current.

When I applied some excitation (maybe 5-10 watts), it did indicate
output and plate current, however not knowing if the meter was reading
correct or not, I did not take much time to measure actual output for
fear of losing the grid.  With 20 to 40 watts of drive, the grid
reading nearly goes off scale with no effect turning the load cap.
SWR is 1:1, so no problem there.

I swapped the tube with a spare known to be good and the results were the same.

At this point, my ideas on the problem are guesswork.  I suspect the
bias diode for the cathode, or the metering circuit for the grid
meter.  Oddly, the schematic shows only one diode D1 for the bias,
however in my amp, there are clearly two in series that appear to be
OEM, so that in itself throws me off.  I plan to take the diodes out
of circuit today and check them for lack of any other ideas.  BTW, are
these Zeners?  The manual just calls it "bias diode".

Also, can anyone tell me what D105 is for?  This is a small metal can
diode hooked directly to R106 on the HV- lead.  When I replaced R106,
I failed to check this diode, and since it is physically attached to
R106 parallel to ground, I suspect it could have been damaged when
R106 blew up.

As you can probably tell, I'm sort of pulling at straws right now, so
forgive the ramblings.

I would really appreciate hearing from any experienced 3K folks that
may shed some light on what I need to be looking at.  In the meantime,
I'm going to find some corona dope and patch up the point of arcing so
that doesn't happen again.

Thanks,
Brian / w5ami




-- 
"There is nothing more uncommon than common sense." -- Frank Lloyd Wright