|[Hallicrafters] SX-25 Troubleshooting Help Needed|
WA1KBQ at aol.com
WA1KBQ at aol.com
Sun Jun 26 09:08:20 EDT 2011
Difficult to troubleshoot when you have original parts which most are
likely degraded (capacitors act like resistors and resistors have drifted
upwards in value over time). A radio not working properly will always show up in
out of spec tube pin voltages. You will need to check them starting with
the RF stages and work toward the audio. Pay close attention to grid #1
voltage with respect to the cathode. To quickly find a stage not working touch
the control grid of each stage from RF forward and it should produce a loud
buzz in the audio. You can touch them with the tip of a soldering iron if
you don't want to use your finger.
In a message dated 6/24/2011 8:43:38 P.M. Eastern Daylight Time,
joeconnor53 at yahoo.com writes:
I picked up a beat-up SX-25 today and need some help.
After changing the 'lytics, the broadcast band (Band 1) plays beautifully.
The set, however, is completely dead on all other bands. There isn't even
static. There is no sound when I disconnect or conntect the antenna.
Jiggling the bandswitch does not help. I have plate and screen voltages on both
the 1st and 2nd RF tubes (6SK7s).
I did signal injection. On Band 2, I got an RF signal from a signal
generator through the 2nd RF with some amplification. (Thanks God for tube
extenders!). I got an RF signal through the 1st RF with no amplification. Even
the amplification I got on the 2nd RF was far less I got on Band 1 (BCB). On
Band 3, I couldn't get any signal through either RF stage.
The set is pretty original. There are signs of a few caps being replaced
in the '40s or '50s. The only modern cap is one orange drop used as a bypass
cap. I'd like to troubleshooting this systematically, rather than simply
blindly replace caps and hope I hit the problem.
Any ideas or troubleshooting tips?
As always, thank you for your help.
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