[Amps] AL-80 ... POW!

[k8bb@comcast.net]

I have an AL-80 (not an A or a B), S/N 808. I was attempting to load it on
17m in the 15m band position. (In retrospect, I know I should have known
better than even to have tried this ... )

I tuned it to about 250w out, but with almost 50w drive. SWR was around 1.5.
IG read around 100ma. I switched the meter to IP, just to check. IP read
just over 300ma, then it made this sound: fzzzt - POP!!! I immediately
turned the amp off.

I didn't really smell anything particularly bad, but maybe just a little
bit. And I vaguely recall maybe seeing a white blue/white flash through the
(added) cooling holes. I also noticed that when I switched the meter into
the IG position (amp off), it (gently) read negative full-scale. After
several minutes, it read zero. I put the meter in the V position and
switched it back on. It went, "Fzzzt." (not loud) and the meter jumped
around a little bit, but did not register appropriate voltage. I turned it
off after about one second.

I opened it up and I see these things:
- There is a little "spot" (looks like damage?) on the plate choke, but it
still has continuity (about 2.4 ohms).
- R6, a 1.5 ohm, 3W, 1% wire-wound-looking resistor has a hole burned in it
and I can see the little wire coil inside. This resistor is listed in the
schematic as being for IG metering.

What do I do next? I cannot imagine that the POW (that sounded like it came
from the RF compartment, not the HV supply) could have been the resistor
burning up. Coincidence? Is it possible that the Plate Choke arced without
seriously damaging itself? Or is it indeed damaged? And why did the amp
continue to "Fzzzt." when I turned it back on, very briefly? What other
"usual suspects" should I look at? I'd be glad to try to take a picture of
the PC if anybody is interested in trying to determine if it is NFG. Where
would I get a replacement?

Please be gentle ... I am learning ...

Don Chisholm
K8BB
Pontiac, MI

P.S. Before posting this question, I searched the archives pretty thoroughly
and I learned that this little gem is not exactly the Zenith of amplifiers,
as far as design and reliability are concerned, and I didn't really find any
troubleshooting advice for this particular model. Instead, I found a lot of
public (though very personal, at times) debate as to what exactly might have
caused this. I am not particularly interested in exactly what caused this,
just how to repair it - I can take care of preventing it on my own.