02-26-2019, 12:00 AM
< Well I did more testing and I think I'm narrowing the problem down to the antenna transformer. Schematic says 7.2 ohms from the wiper of the volume through the coil. I'm reading 2.4 ohms .
Typically when the ant coil (primary) is bad it's open, from rotting or lightning. Check the other runs/code# of the model 38 and you may find one that matches yours.
<Can I inject sound from another source like a CD player through a capacitor at a point after the oscillator to verify?
No. If you are using an audio source you will only be able to use it to test the audio portions of the set. The mixer, IF amp, and detector are designed to respond to a rf signal. In these stages you would use a signal generator.
Reread the bottom portion of post#5 and complete the IF alignment.
Once that is done take another radio and place the ant wire or loop near the 1A6 tube. Tune the dial on the 38 to 1000kc (100 on the dial). Tune the 2nd set to roughly 1460kc. What we are doing is we are listening for the oscillator signal from the 38. In a perfect world it would be 460kc more that the dial setting. It = dial setting + the IF frequency (460kc). If it's working you will hear strong hum or hiss as you tune across it.
Typically when the ant coil (primary) is bad it's open, from rotting or lightning. Check the other runs/code# of the model 38 and you may find one that matches yours.
<Can I inject sound from another source like a CD player through a capacitor at a point after the oscillator to verify?
No. If you are using an audio source you will only be able to use it to test the audio portions of the set. The mixer, IF amp, and detector are designed to respond to a rf signal. In these stages you would use a signal generator.
Reread the bottom portion of post#5 and complete the IF alignment.
Once that is done take another radio and place the ant wire or loop near the 1A6 tube. Tune the dial on the 38 to 1000kc (100 on the dial). Tune the 2nd set to roughly 1460kc. What we are doing is we are listening for the oscillator signal from the 38. In a perfect world it would be 460kc more that the dial setting. It = dial setting + the IF frequency (460kc). If it's working you will hear strong hum or hiss as you tune across it.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got it!
Terry
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