Quote:
Originally Posted by Electronic M
I just recapped mine over the course of two days.
I have a hunch your repairman did not try to understand the audio circuit on these. The thing to know on these is that the there is no fine-tuning because the ratio detector in the audio circuit doubles as an AFC/AFT circuit (*!)...Basically, there is a feedback loop that adjusts the tuning at the tuner's local oscillator to tune for best sound based on the DC offset at the ratio detector in the audio stage. If the audio IF and or ratio detector is out of alignment the circuit will stumble all over it's self to compensate and the results will be lousy intermittent unstable distorted sound...And the AFC will make aligning it by ear more difficult. Mine after the recap had weak intermittent distorted sound with lots of video noise...To fix it I had to disable the AFC by grounding the AFC line, (check the local OSC adjustment), then tune the IF cans for max volume/minimum video noise and adjust the ratio detector for minimum distortion, then unground the AFC line. The sound was nice and stable after that.
There is still a bit of video noise, but not much compared to some sets. Volume is a tad less strong than I would like, but then again broadcast TV audio carrier levels dropped substantially within a few years after they made this set so many of the early sets of all makes have diminished max volume levels baked into their design.
*It is very interesting to me that Philco put an AFC/AFT circuit into this set. It was around two decades ahead of its time (I have not seen many sets pre-1968 with AFT). It is also interesting that they were confident enough in it to not provide the user a fine tuning knob.  |
Very good work! My repairman told me, years after he restored the chassis on my now sold-off 48-1000, that he could've done something with audio. Someone doing a repair job will rarely put the amount of hours into it as the owner of the set.
I've owned many vintage TV's over the years, but a good working early post-war Philco has always alluded me. I had 2 and sold them. You just can't beat Admirals, RCA's, GE's, and Motorola's if you like to use the sets.
Enjoy your Philco!