On Nov 13, 6:58*pm, "Richard Knoppow" wrote:
"Nordic Breeds" wrote in message

...



"Richard Knoppow" wrote in
message
om...

"tchrme" wrote in message
....
Partial success on this stubborn problem and it would
have to be my
favorite rcvr too. I traced the thunderstorm crashing
sounds down to
the 2nd converter subchassis. After I pulled it again, I
replaced all
the caps and the resistors since it is such a pain to
access. I
powered it up on test leads to the main chassis and
still heard the
frying thunderstorms. A 22k resistor that I replaced was
starting to
overheat and turned brown. I checked the one I took out
and it too was
burned looking. So.... I need help on what would cause
the overheated
resistor (R24). I can email a schematic to anyone who
can help me out
on this. I double checked all wiring and parts were
replaced one at a
time. Help. *Thanks ahead of time. 73 Mike KF6KXG

* * Have you made tube socket voltage and resistance
measurements? This is a first step and will often point
at problems. I've downloaded the schematics for both
versions of the RX, you appear to have the earlier one
(the 22K resistor is a different value in the later
version). I can't see an immediate suspect but any
capacitor in a position to draw current through the
resistor is a suspect. While paper caps fail mostly by
developing a low series resistance I have encountered
shorted ones.

Both the Mark 1 and Mark 2 models have the 22K resistor in
the Bama schematics. *I would check
both C24 and C26 but a leaky C24 is the most likely cause
of overheating in the 22K resistor. *A
quick check on the plate and screen voltages of V5 should
point you in the right direction. *A tube
socket extender is handy here, but carefully pulling the
tube out and carefully wrapping a fine wire
around the appropriate pins and plugging it back in will
work. *C28, C29, and C30 should also be
checked. *Silver migration in C28 and C29 could
conceivably case the noise too.

* *73, Barry *WA4VZQ

* * Looks like a different value to me but both schematics
are sort of low res.

--
Richard Knoppow
Los Angeles
WB6KBL


Success! Yes! Thank you everybody for all the help. Because of
the location of V5 in a TIGHT corner of the subchassis I didn't check
its voltages until I used lots of test leads and fired it up on the
bench out of the rcvr. Not only was the screen grid reading low but so
was the plate. It should have been around 270v and was only 17! So
after making sure there were no shorts on selectivity switch circuit
off the screen grid I focused on the plate circuit. The only component
I hadn't changed yesterday was a 100 pf tubular ceramic cap that
ohmed out in the megs. Silly me, I thought it was good. Well it was
the first component to ground after the plate so....I decided to lift
a lead just to be sure. Wow, everything went to normal voltages and
the crackling stopped. I subbed in a new ceramic cap and let it run
for a while on the bench. All was good so I put it back together and
aligned it. Colin, you were dead on. It was C 27. I just figure the
cap was partly open and under high voltage, broke down to a short that
varied in degree that caused the thunderstorms. While I also replaced
V5, V12, and V13 in case of a grid to plate short as Paul suggested,
my Paco tube tester did not indicate any shorted elements, but then
again I am going to check them with an VOM when I get a chance just to
know. Barry, I had the same thought on silver migration, so the first
thing I did was to change the silver micas.
Again, thank you to all who helped to point me in the right
direction. Sometimes we get so close to a problem, we miss it and
another person viewpoint is needed. Have a great weekend, 73 Mike
KF6KXG