Newbie's First Questions RCA TS 721 Restoration

[Notimetolooz]

Originally Posted by Chris K

When I hooked the Leader up to my Zenith for testing, there was a tone. I'll check again this evening. My Conar generator definitely has one. Yes I have a Tektronix and a Heathkit scope

Some other generators do have sound modulation. The LGC-396 doesn't seem to.
That generator can only output channels 5 and 6.
That may be a problem if you want to adjust channels 3 or 4 on the tuner so that you can use it with the digital TV converter.

The suggestion that you might be able to use the output from the digital converter to align the sound could be a good one. If you arrange to not receive a station on the convertor it may put out a sound carrier without modulation.
You then might be able to peak the sound IF and adjust the discriminator for zero volts output. Using a scope would be the best way to see the results.
You would first need to make sure the tuner was adjusted correctly.

[Penthode]

Originally Posted by Notimetolooz

...
You then might be able to peak the sound IF and adjust the discriminator for zero volts output. Using a scope would be the best way to see the results.
You would first need to make sure the tuner was adjusted correctly.

Unfortunately that will not work here because we are dealing with a split sound set and not intercarrier! Because the set top box goes through the tuner, the fine tuning (local oscillator) in the tuner will change discriminator zero. In fact, when the set is properly aligned, each time you change channels, you are always adjusting the fine tuning for discriminator zero!

You must use only a crystal calibrated 21.25MHz oscillator applied to the IF input to initially set discriminator zero. You cannot do it with anything applied to the antenna terminals.

I would not worry about discriminator zero at this point because the ball is out of the ballpark. Let us find the audio first and then find a way to set discriminator zero.

I have a deep hunch the 5.1 ohm filament resistor is bad.

[Chris K]

Originally Posted by Notimetolooz

Some other generators do have sound modulation. The LGC-396 doesn't seem to.
That generator can only output channels 5 and 6.
That may be a problem if you want to adjust channels 3 or 4 on the tuner so that you can use it with the digital TV converter.

The suggestion that you might be able to use the output from the digital converter to align the sound could be a good one. If you arrange to not receive a station on the convertor it may put out a sound carrier without modulation.
You then might be able to peak the sound IF and adjust the discriminator for zero volts output. Using a scope would be the best way to see the results.
You would first need to make sure the tuner was adjusted correctly.

The Leader has a channel 3 or 4 option for output...not 5 or 6. Its LCG 396...not LGC 396. Maybe that's the issue

[Notimetolooz]

Originally Posted by Chris K

The Leader has a channel 3 or 4 option for output...not 5 or 6. Its LCG 396...not LGC 396. Maybe that's the issue

My typo.

The manual I found doesn't mention options. Perhaps yours is a later version.
http://bama.edebris.com/manuals/leader/lcg396/

You could use a sig-gen with AM modulation (1KHz) on 21.25 MHz to inject the signal at the output of the tuner. Trace it thorough the sound IF with a detector probe attached to a scope. You could not get the sound any further than the discriminator, however you could confirm the sound IF transformers were peaked correctly. You could check the 21.25MHz with a frequency counter if need be.