'49 Admiral audio problem

[kbmuri]

Wa2ise -

I tried loosely coupling the VCR signal on Monday -- forgot to report it. With a snowy picture, I get correspondingly weaker sound (less than 10% of normal). Sounds I would expect of a working TV, just quieter.

The "bar generator" is generating AM. It's just a standard sine-wave generator, amplitude-modulated with a fixed tone (middle-C?). The sine wave frequency is adjustable from a few kHz to many mHz. The tone is not adjustable.

The effect is bars when tuned to the video frequency, and tone when tuned a few mHz higher. It does this on all my TVs, old and new.

I have a battery-powered 1-inch Sony Watchman on the workbench for reference. I tune the (variable) tuner to Ch3 or Ch4 first, using the VCR as input. Then it shows bars when the Unit-Under-Test shows bars, and sounds a tone when the UUT sounds a tone.

You are correct, the Sony's tone goes to dead silence when the signal generator is "dead on", but is nice and loud on either side. I believe the UUT was doing the same thing, but I need to verify this.

The signal generator will produce an audio tone on my Magnavox PLL digital-tuner pocket radio. I use this radio for calibrating the generator. AM and Shortwave bands sound clean, FM is distorted. I will try seeing if the radio "silences out" when an FM frequency is tuned dead on. I suspect it will.

The C5 Electrolytic is new from Mouser.com, fresh stock. It's a 4.7 mF, not a 4.0, if that makes a difference. I didn't put it on a cap checker though (even though I have one). Lazy, I guess. I'll doublecheck it.

The R48 resistor is a little low, about 4 Ohms even. I don't have any 4.7's on hand.

I'll check the voltage at the 6AL5 filament.

I've rocked all the tubes in their sockets and swapped/rotated them all. No apparent effect. Nothing seems loose/dirty.

I will try tuning to Ch.6 and trying for some FM stations. I flipped the tuner thru the cycle once or twice and don't recall any, but I wasn't looking for it.

Excellent ideas, thanks!