[Hallicrafters] SX-42 Hum(bug)

[Peter Sturdivant]

Hi Mike,

I restored a 42 a few years ago.  It's a good project.  As to the receiver
issues, you're going to have to troubleshoot rx stages.  Where you have
hum...the audio stages seem to work.  Do you have an O scope?  This is most
helpful to look at the stages.  Make sure the B+ is OK.  Is the meter dead
too?  I can't recall what IF stage the meter is in...probably one of the
last stages.  If dead, you have a dead stage in the RF or IF section.

Don't replace anything else until you get the radio working (you could ADD
troubles).  When that's done, you can then replace the caps and bias
resistors (the ones that are bad).  I seem to recall on my 42, that most of
the screen and plate resistors were way off (replace if off by more than
10%).  Doing this will improve the performance of the rx but is not the root
cause of your dead rx.

73,
Pete
n1ps


----- Original Message -----
From: "Mike Smout" <mikesmout at sympatico.ca>
To: <hallicrafters at mailman.qth.net>
Sent: Monday, July 29, 2002 6:53 AM
Subject: [Hallicrafters] SX-42 Hum(bug)


I've completed the first part of the SX-42 restoration which is the cosmetic
part. After sliding the chassis back into the cabinet I built up the nerve
to power it up. I know what you're thinking, but I do not own a Variac and
the temptation was great. Everything lit up, no smoke, no flames etc. All I
got was a hum. My first thoughts are that the electrolytics are shot, so I
purchased an entire set of caps *yikes what a job this is gonna be* and will
proceed to replace them, at least the ones that I can get at. The chassis is
super clean and it appears that there is no leakage from the paper caps.
Also, it appears that no one has done any modifications to it at any point
in its life. I have tested some of the tubes and a couple are testing border
line. Assuming that the electrolytics gave up the ghost, could this have
damaged some of the tubes if it were left on for a period of time. I would
welcome your suggestions on what to, and what not, to do. Thank you in
advance. I also looked at the bandswitch mechanism and switched it with the
power on to look for any of the famous "shorting out" and it doesn't do
this. Thanks, Mike Smout


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