Quote:
Originally Posted by Kevin Kuehn
Couldn't one hook his digital to analog converter box set to Ch 3 or 4 rf carrier(no antenna) to the set's ant input and monitor the DC voltage at the output(pin 1) of 6AL5(V116) sound discriminator? With the TV's ch selector set to the corresponding carrier frequency it seems pin 1 should be at or very near 0v DC when everything is aligned correctly. If this works I'd set the fine tuning to center and adjust the Ch 3 or 4 oscillator slug in attempt to read 0 DC volts at pin 1. This assuming the sound IF and discriminator adjustments are very near their previous tampered with settings.
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Yes you could. However you will hear the audio as you are tuning the slug long before you will have anything intelligible on the meter. Further you can hear when it is tuned as you will be tuning between the two distortion peaks if the discriminator is properly aligned for a perfect s response. The alignment remains suspect now because the settings have been changed. But even if the alignment is bad, you should hear something.
So the first rudimentary step is to try and bring the local oscillator back in line. I suspect a simple swap around of the tubes will yield some audio. Then we can focus on its precise final adjustment.
Which reminds me that split sound TV tuning is no different from an FM radio tuning which uses the discriminatory circuit. That is as you approach the correct tuning, the audio builds in level, becomes distorted then the loudest and clearest audio is received. Tuning further you reach a second distortion peak and the audio clears and is weaker. Many forget that either side of the best audio point is slope detection which is weaker and slightly distorted.
But here, we first need to hear any audio and the home in on it.