Model 70 plate to ground question. - Printable Version
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Model 70 plate to ground question. - radio1 - 06-24-2020
Still working on this unit. I measure 7k ohms first detector (converter 2nd 24 tube) plate to ground - all tubes installed playable unit, the volume control does nothing to alter it. Is the first IF coil leaking or normal?
https://www.philcoradio.com/images/phorum/schem/70a.jpg
RE: Model 70 plate to ground question. - morzh - 06-24-2020
No it is right. Your wirewound #37 divider plus the #36 field coil and the F to G volume regulator do this.
Simple test, remove the speaker, then the curcuit should become open.
RE: Model 70 plate to ground question. - radio1 - 06-24-2020
Shouldn't the volume control vary the ohms? The volume intercepts the wireround, my field coil is just resistors.
RE: Model 70 plate to ground question. - radio1 - 06-24-2020
I removed the speaker, still obtained 7k ohms.
RE: Model 70 plate to ground question. - Steve Davis - 06-24-2020
7K sounds like a good number. You have the winding of the IF transformer, a field coil, the volume control and three resistors in the BC resistor all in series to ground, should come out pretty close to 7K.
Steve
RE: Model 70 plate to ground question. - morzh - 06-24-2020
You mean you UNPLUGGED the speaker altogether and still got 7K?
Oh...wait, you have permanently replace Field coil with the equal value resistor?
Then yes, unplugging the speaker will not affect anything and this will remain about 7K.
And no, the volume will not vary anything. Not just because it is low value compared to the rest of the divider, but the wiper is not part of the circuit.
RE: Model 70 plate to ground question. - radio1 - 06-25-2020
Thanks for info, whew for me, the volume control confused me, but I guess it's a path to nowhere until fired up. Thinking about it, what a wonderful upfront test to check for failure areas.