[Boatanchors] SX-25 Troubleshooting Help Needed

[Al Klase]

Joe,

Check that the local oscillator is running.  Do one of the following:

    * Put a scope probe near the oscillator coil, or front section of
      the variable cap.
    * Listen for the oscillator with a second CW receiver.
    * Observe a negative voltage on the oscillator grid.


Check the value of the 6K8 oscillator grid resistor.  May have aged high.
Check the voltage on the 6K8
Try another converter tube.

Good luck,
Al

On 6/24/2011 8:43 PM, Joe Connor wrote:
> 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.
>   
>   
>                             Joe Connor
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/