Riddle me this, Batman

[Paul K. Dean]

OK, here's one for all you former Heath engineers, technicians, historians,
repair people!

If you remember a couple of days ago, I asked for ideas on fixing an HW-12A
that was sluggish going into transmit.  I had traced the problem to a slow
decay of the cutoff bias from the ALC filter cap.  By the way, thanks to
all that replied.  Most folks suggested leaky ALC diodes and mentioned that
had been a big problem in the past for many folks.  Replaced them, didn't
help.  No problem, they'd probably go bad someday anyhow.  A couple people
suggested gassy finals.  Swapped with a good pair, still no good.  Also had
a suggestion that the capacitor between the ALC and the final grids was
breaking down.  Leak tested it at 500 volts, checked OK.  Replaced anyway,
still no good.

So...... I'm trying to figure out why my HW-22A, HW-32 and HW-32A all
work?????  Then I notice..... all of the other rigs use a .2 or .22 mf
capacitor and a 1 meg resistor in the ALC filter (even the HW-12, for which
I have a schematic but no rig!).  The HW-12A uses a .47 mf cap and 2.2 meg
resistor.  About 4 times the time constant, hmmmmm.  Replaced them with a
.22 and 1 meg, now the rig seems to work fine.

So, my question...... what happened?  Is my HW-12A a "new and improved"
model or did it miss out on an engineering change?  Was there a special
reason that the HW-12A's ALC filter was different from the other rigs (both
"A" and non-"A")?  What's up, guys and gals?  Trivia time!

(I have another HW-12A "fixer upper" on the way from another gentleman on
the list.  Interested to see how this one will react.)

Thanks, all.  Happy Holidays and 73,
Paul, wb9hgz

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