Help needed with Halli SX 100 repair

[tchrme]

I need tjhe wisdom of the list as this one has me totally stumped. A
week ago I posted about static crashes on this rcvr. The collective
advice was to check out the stages by removing tubes and then replace
the micas (which are discrete components on this rcvr) in the IF cans.
Well, the first tube that made a difference by removal was the 50.75
KC IF amp (6C4 V13) on the 2nd converter IF chassis so...I bit the
bullet and pulled the subchassis. Easier said than done on this rcvr.
I replaced the micas associated with T3, T4, and T9 the cans on the
subchassis. Still had static crashes...so I replaced all the IF micas
in the other cans while I was at it. Aligned it and sensitivity is
great but still static crashes. I thought maybe the C31 mica which
carries the signal out of the subchassis to V13. Tried subbing a cap
in and same result. The funny thing is that when I put my signal
tracer on V4 or T2 which is the 1st IF amp, I can hear the crashes,
but removing the V4 tube doesn't have an effect. Also removing the
tubes V5 and V12 on the subchassis doesn't stop the crashes. Several
questions. Could the static crashes be back feeding from the
subchassis to T2 or is the problem in that stage? Besides micas what
other component failures should I be looking for? Can a bad tubes
cause it? Thanks in advance for help. Mike KF6KXG

[COLIN LAMB]

I have had "static crashes" due to dry electrolytics. If you have a scope,
you might watching the dc lines to see if you can observe any of the
"crashes" there. I would also replace all of the paper caps.

It could be a number of things, such as a poor ground caused by oxidation or
even a noisy resistor. A scope should be able to help you isolate the
general area.

Note that if it is a bad electrolytic, often paralleling a good one will not
eliminate the crashes. The bad one needs to be removed from the circuit.

Hang in there. We all go through this at one point. I remember my friend
had a microphonic mica cap iinside an if transformer of his NC-183D. He
worked on it every night for 6 months until he found it.

73, Colin K7FM

[tchrme]

Colin,
Thank you for your recommendations. I replaced all the
electrolytics 5 years ago when I got the rcvr. When I pull the 2nd IF
tube they go away. So I don't think the electrolytics are the cause. I
have tapped all the resistors and remaining micas (except the
subchassis because it was removed) and nothing is microphonic. Does a
resistor or mica have to be microphonic to cause the crashes? Mike
KF6KXG