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Philco 38-690 Oscillator Not Working?
NV3G
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City: Shinnston, West Virginia State, Province, Country: USA
#1

04-02-2019, 07:53 PM
I have strong audio signals and strong IF signals. I am receiving no stations at all.

The local oscillator does not seem to be working. Oscillator voltages are as follows:
Pin 3 - 191.8 VDC
Pin 4 - 93.0 VDC
Pin 5 - 1.58 VDC
Pin 6 - 195.5 VDC
Pin 8 - 2.53 VDC
Grid Cap - 0 VDC

The mixer voltages are as follows:
Pin 3 - 238.1 VDC
Pin 4 - 99.7 VDC
Pin 5 - 1.58 VDC
Pin 6 - 99.7 VDC
Pin 8 2.53 VDC
Grid Cap - 0 VDC

Shouldn't the pin 5 of the oscillator grid measure a large negative voltage? Does the OSC CONT tube
have control over the oscillator?

Thanks for any suggestions and help.
nv3g
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Radioroslyn
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Threads: 268
Joined: Dec 2009
City: Roslyn Pa
#2

04-02-2019, 08:41 PM
>Shouldn't the pin 5 of the oscillator grid measure a large negative voltage?

I wound think so also the control grid of the mixer too as they wired together.

If you are not seeing any -voltage there you may want to check the normal suspects. These being a dirty band switch, weak 6A8, or bent plate on the osc section on the tuning cap. Did you replace ALL of the foil paper caps in the sub chassis? A missed one could kill the osc. If you removed the sub chassis is it wired in properly?

>Does the OSC CONT tube have control over the oscillator?

Yes it does via the magnet tuning circuit. Don't think that it would stop the osc from working.
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
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