HQ-145AX puzzler

[Wally Gibbons]

Greetings,
Just picked one of these up in great condition (and three zenith
Transoceanics too!) the other day. It needed some minor repairs, the
little audio coupling circuit between the 12AX7 and 6AQ5 had failed and
applied positive grid bias to the output tube, frying the cathode
resistor. Tube still checks ok, amazing!!!

But now, it's problem. It plays fine, then the received level will drop
(at random, apparently), as will the s-meter reading. If I switch the
vfo/crystal switch one position off and back to VFO, it comes right
back. In fact, a good foot rub and then a "spark" of esd which causes a
pop in the received signal will do the same thing. Any noise burst,
disconnecting the antenna and reconnecting, will restore the previous
receive level. I've never had a radio which behaved this way, obvious
checks (tubes, cleaning the switches, pots) haven't helped. Doesn't
appear to be a loose connection. Mechanical tapping around doesn't cause
it to happen, or fix it. Could it be that other printed circuit module
in the AVC/detector circuits?

Anybody had any experience with this? I've heard stories of intermittent
mica caps in the bottom of IF transformers and suspect this might be
that. Any pointers as to where to look?

Thanks.

Wally Gibbons, WB7ASQ
North Logan, Utah

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