[AMRadio] Winter

[Todd, KA1KAQ]

On Fri, Oct 1, 2010 at 10:50 AM, D. Chester <k4kyv at charter.net> wrote:
> I had the same problem with  my HF-300 rig.  It would happen only
> occasionally, but often enough to be annoying, and I kept running out of
> fuses.  It went away when I replaced one of the sets of 872-As with 4B32s.
> I still have some unused 872s, but I am using the xenon replacements right
> now. I must have a bushel of used 4B32s that I picked up back in the late
> 60s, pulled  from military transmitters that had been taken out of service.
> Only a couple of them have ever  flashed over, and I promptly threw those
> away.

Yep, that was the main problem with the transmitter when I first got
it on the air. MV flash overs galore. Put in new 872s and before long,
the same issue. Switched to the 4B32s about ten years back while off
the air (was working on the rig into a dummy load) and those flash
over issues disappeared.

I *think* I found source of problems in the tank circuit, and it's not
at all something you'd expect. There are some indications that there
has been an intermittent HV issue with the rig for many years, from
notes in the manual and such. I'll post photos of it on 'fone later
once it's all done, but suffice it to say it involves a feed thru
insulator handling HV breaking down to ground in a way I've never seen
before, and never thought possible. Others with this transmitter have
had similar problems, but the particular failure mode really surprised
me.

Though it looks like the culprit, I won't know for sure until it's
reassembled and back on the air to test. Need to see if I can dress
the plates on the loading cap under the deck with some crocus cloth
before buttoning it up. Too much of a bear to remove this one, but
fortunately I can only see a few tiny bright marks on the edges that
look like they were caused by arcing.

Heard you on last night Don down on 05, was reinstalling the loading
cap and listening. You'd left by the time I finished up at 1:45AM.
Think I invented some new swear words trying to get one of those
silver straps from the band switch reattached to the side of the air
variable.

~ Todd/KAQ