[HBR] HBR-14 (and a half) sanity checks

[shoppa_hbr at trailing-edge.com]

OK, it seems my HBR-14 has some things that make it no longer a
"stock" HBR-14: BFO, product detector, and first audio stages 
seem to be lifted from the HBR-16 with the transliteration
of a 6SN7 for 12AU7.

But that end of the radio seems to be working fine. I'm moving
my attention to the front end.

I'm trying to tune it up to work on 40M right now.

I can tweak the 1st oscillator coil cap and zero set so that when
the dial is most of the way to the left, the osc is at 8600 kc.
I'm doing the math right, 8600-7000 = 1600kc, the first IF, can
someone confirm that sanity check? As I turn the knob to the
right the HF osc goes through 8700, 8800 kc so I think I'm
in the right range. (All freqs measured with a loosely coupled
loop on the HF osc. If I put a scope probe anywere in there
it pulls by hundreds of kc.)

Anyway, the calibrator comes in quite clearly at 7000kc
nearly pegging the S-meter. I know it's the calibrator
because if I turn it off it's gone :-). With the calibrator
on I also hear a weak signal at 7080kc, but that's goes on and
off too, so it must just be some leakthrough somewhere.

If I advance the IF gain too far, the audio becomes squirrely,
this means the IF is breaking out into self-oscillation at this
point, right? So I just don't turn the IF gain knob that far up.

The RF gain pot is clearly shot, because if I don't have it
cranked all the way to the right then the calibrator drops way
down and no RF knob action does anything anymore. In fact it
sounds exactly like I set the switch to "transmit" in this case.
I don't know where to get a 7500 ohm 2W wirewound pot, but maybe
I can either fix it, or just sub in a 5K or 10K wirewound pot
here.

But even though I can hear the calibrator quite clearly and
peak it with the trimmer so that it's nearly pegging the S-meter,
I don't actually hear any CW on the 7000-7100kc segment where
I know there has to be activity. In fact all I hear is something
that sounds like Radio China or Radio Taiwan when I hook up an
antenna and there's no change as I turn the tuning dial.
I'm guessing there's something else in the front end
that's severely out of whack. I'll be checking over the coils,
I guess.

I can peak up the RF input coil (L1) quite nicely with the trimmer on the
calibrator, and there's no pulling of the HF osc when I do this. But
any even slight adjustment to the mixer coil (L2) trimmer cap will
send the HF Osc zooming across the band (hundreds of kc), or just plain
stop it from oscillating. I don't think that's supposed to happen!
The coupling between HF osc and mixer
is just the gimmick. Maybe that damn 6AH6 is breaking out in self-
oscillation? I built a VFO out of a 6AH6 once and it just loves to
oscillate at 400-500Mc even though it was supposed to oscillate
at 3.5Mc :-).

Tim.