07-12-2019, 01:12 AM
Tested the tubes and most were pretty good but the two 78's (IF amps) and the 77 (mixer) were not so hot. Found a few replacements and gave them a try. Fired the chassis up and all was well but the sensitivity was poor and volume low just picking up a few local flamethrowers. A cursory check didn't yield any obvious issue so it was time to break out the signal generator. Got it warmed up and set up for 460kc. I was surprised that the 460kc trap works really well and has a nice sharp dip in signal. The If transformers were way out of adjustment. After repeaking them a couple of times to be sure they were on frequency the sensitivity was restored to what it should be. Obtw the 2nd transformer was ok.
The dial calibration was off on the bc band abt 40kc. This may have been because of retuning the IF to match the replacement transformer. Anyway I was reading the alignment procedure and it seemed kinda confusing, I'm thinking it's because the generators used back then were not so accurate so they used a crystal to hetrodyne a harmonic to come up with a reasonable close frequency to align to set. With that in mind it's just a matter of sorting which trimmer adjusts what frequency. Got the bc band in good calibration. I'll tackle the short waves tomorrow.
The dial calibration was off on the bc band abt 40kc. This may have been because of retuning the IF to match the replacement transformer. Anyway I was reading the alignment procedure and it seemed kinda confusing, I'm thinking it's because the generators used back then were not so accurate so they used a crystal to hetrodyne a harmonic to come up with a reasonable close frequency to align to set. With that in mind it's just a matter of sorting which trimmer adjusts what frequency. Got the bc band in good calibration. I'll tackle the short waves tomorrow.
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!
Terry