I got a fixer-upper Hallicrafters SX-140 and its driving me batty.
After resolving a number of problems I found that both the IF xfmrs
needed some surgery (bad mica sandwiches). I've replaced them, the
IFs seem to be peaking ok. BTW, the magic value in these seems to be
325-330pf.

I still can't get the darn thing to regenerate. AVC doesn't work
either but right now its the regenning that is my primary problem. I
can hear plenty of stations...the broadcasters on 40 sound fine and I
can hear the CW contest going on. Anybody know the magic clue that
I'm missing? Anybody know what sort of voltage range I should be
seeing on the suppressor of the 6BA6? I'm only getting a swing from
about zero to two volts and it has zero effect on the signal. My pot
was open and has been replaced. The diode is ok as are all the normal
components.

I'm a tad low on B+ voltage but only by about 10%. Not sure
why...line voltage is around 116-117 at the moment.

I really don't understand how this circuit regenerates. Maybe if
someone could explain that I'd be in a better position for
troubleshooting.

73 and Tnx,
Bill - W X 4 A

"exray" wrote in message
...

I really don't understand how this circuit regenerates. Maybe if
someone could explain that I'd be in a better position for
troubleshooting.

73 and Tnx,
Bill - W X 4 A

They apparently vary the suppressor grid resistance to ground; it uses
the internal capacitance between the plate and control grid to provide
the regenerative feedback. Moving the suppressor further from ground
deminishes the isolation the suppressor normally provides between the
plate and G1.

Pete k1zjh

Just to follow up...

I ordered some proper silver mica caps for the IFTs and that seems to
have made the difference. I had been tinkering around using ceramic
discs that I had on hand, replete with their long leads.

FWIW, I wouldn't have thought that the cap quality would have made so
much difference, nor that my one-inch leads would have terribly upset
anything but apparently so. Although the IFs tuned correctly with the
ceramics it did feel 'broad' and AM signals seemed broad on the dial
as well.

After installing the first set of micas it was noticeably sharper
tuning and while repeaking after installing the second pair the rig
popped right into oscillation as it should.

So my mystery is resolved and maybe this experience will assist
others. For reference purposes...and this may apply to other
Hallicrafters 1650 kc IF transformers as well, the mica caps I used
are 330pf and the coil range is in the neighborhood of 20-30uH, mine
were found ~27uH and the best measurement I could get off of one of
the bad original micas was 325pf.

73,
Bill W X 4 A