Well, something new for me to watch for. Never knowingly had that issue but will be aware. I always re-cap to include the four modules, the BFO, and Xtal filter cans. Point of failure in the R model and others are the trimmer caps on the modules. The retaining collar splits allowing a short. Design of the J, N, and Q model caps are better.  But, I guess that 75-80 years, and sometimes poor environment, can spoil any soup......
JJeep K3HVG
On 08/10/2022 1:34 AM JAMES FALLS <[email protected]> wrote:


1- No ESR meter, but I have an Eico 950B that I reworked a of couple years ago (new caps, resistors). It applies applies around 250 VDC to caps under test and appears to measure leakage well.

2- Should I leave the burnt resistor in place at that 4-way junction for the leakage test, or lift one end of it? (I have replaced cap 11-9 with a modern unit.)

3- I will re-check the 1st IF tube (6K7). Be sure I got the settings correct 😀. My Hickok 600 was happy with it. No shorts indicated, well above the mutual conductance listed.

This is great information ! I NEVER heard of that Chernobyl resistor!

Jim K6FWT

On Aug 9, 2022, at 19:24, David Stinson <[email protected]> wrote:

P.P.S.
If you have an "active" cap checker like the ZM-11
which can ready leakage current, connect it
(with 57-3 out of the circuit and cap 11-9 either
double-checked or disconnected)
between 1st IF pin 3 and ground.
If the meter shows any leakage current to ground, the
first thing I would suspect would be that IF can wafer.
D.S.

On 8/9/2022 9:07 PM, David Stinson wrote:
Resistor 57-5 is the Plate B+ resistor for
the 1st IF.
There are two ways to burn-up this resistor.
Either there is a short somewhere between it
and the plate of 1st IF, or the resistor failed
by drifting lower, thus drawing higher and higher
current until it burns up, like the infamous
"Chernobyl Resistor" of Johnson Ranger fame.
The most likely suspect is indeed capacitor 11-9.
Is your tester passive or does it apply 200+ Volts
to check it for leakage?
Put your Ohm meter from the junction of 547-5, 11-9,
35-1 and coil 119, and the other lead to ground.
This should read a fully open circuit. If there is
leakage to ground, you need to find it.
If you don't find anything that would leak the B+
to ground, I would double-check the first IF tube
to see if it is weak. If so, the resistor could
have drifted low, which would raise plate current to
the point the tube gives up.
If the tube is good and you don't find a short
ground, the next suspect would be capacitor 35-1
shorting and also raising the tube current, enough
to slowly roast the resistor.
If you find no leakage to ground as above, replace
resistor 57-5 and watch it for overheating.
GL OM ES 73 DE Dave AB5S
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