Old Gernanium Transistor Repair

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I was just thinking are you shure it is the oscillator ?

Tune near the bottom of the band take another radio and try to tune to
the oscillator probably 455Kcs above tuned frequency, listen for a dead
spot with a little background noise, that changes when the dial is
rocked slightly on the defective radio. Do this while the radio works
then chill it and see if you can still tune the oscillator or not,
don't change the dial on the now cold radio.

Yes, did that and the oscillator definetly stops at low temperature.
Measured HFE was 75 so I switched the oscillator transistor with
another germanium with HFE of 220. Performance improved, but oscillator
still stops at 40 degrees F or lower. I also switched the last IF with
a high gain silicon and adjusted the bias and retuned the coils.
Performance again improved, but radio still has noise problems on weak
stations. The signal trimmer capacitor peaks near the center of the
range, so I'm pretty sure the front end is aligned correctly. The noise
must be coming from one of the IF stages.

If I can fix the noise problem, the thing should work as good as new at
moderate temperatures.

-Bill

 

[Homer J Simpson]

Yes, did that and the oscillator definetly stops at low temperature.
Measured HFE was 75 so I switched the oscillator transistor with
another germanium with HFE of 220. Performance improved, but oscillator
still stops at 40 degrees F or lower. I also switched the last IF with
a high gain silicon and adjusted the bias and retuned the coils.
Performance again improved, but radio still has noise problems on weak
stations. The signal trimmer capacitor peaks near the center of the
range, so I'm pretty sure the front end is aligned correctly. The noise
must be coming from one of the IF stages.

Check the voltages on the bases of the first one or two transistors at
different temperatures. Check all of the resistors - if you have a low
voltage meter that can test without turning the junctions on use it.

 

[[email protected]]

R! wrote:

Yes, did that and the oscillator definetly stops at low temperature.
Measured HFE was 75

then your problem certainly isnt the transistor.


NT