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A little help Please - Printable Version

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RE: A little help Please - elfiself - 03-07-2018

Terry what are the proper connection points for the #12, 27K ohm resister ? The schematic is confusing and my interpretive skills are weak. Looks to me like pin 5 on #9 and pin #3 on the 7B7. Then a connect from pin #3 on 7B7 to pin #5 G3,5 on the 7A8.

RE: A little help Please - Radioroslyn - 03-07-2018

Perhaps this will simplify it for you.
The HV is directly connected to the bottom on the output transformer, SG of the 50l6 (pin4), bottom end of 20 (1st audio plate resistor), bottom end of 13 which in turn feed the plate of the IF amp, bottom end of 10 which in turn feeds the plate of the 7A8 mixer, pin 5 of the osc coil, and the left side of 12. The right side of 12 feeds the SG voltage to 7B7, grids 3 and 5 on the 7A8 and is bypassed thru 11 back to B-.

RE: A little help Please - elfiself - 03-09-2018

Hi Terry, just found a dead short on the oscillator side of the tuning capacitor. The stator is shorted to chassis even when the variable cap is wide open. Have to check how its isolated from chassis. Was hoping not to have to remove from chassis. We'll see.
Elfiself

RE: A little help Please - morzh - 03-09-2018

Are you sure you are not seeing the low resistance of the coil 9 across it?

RE: A little help Please - elfiself - 03-09-2018

Well I just spent an hour with a 15X glass, inspecting the fins and couldn't find a problem. What do you suggest to verify the coil effect?

RE: A little help Please - Radioroslyn - 03-09-2018

< What do you suggest to verify the coil effect? 
Disconnect the wire from pin 2 in the coil. This will break the ground connection thru the coil. With that disconnected the tuning cap should read open.

RE: A little help Please - elfiself - 03-09-2018

Bingo !!

RE: A little help Please - elfiself - 03-10-2018

Looking at the 42-PT7 schematic can you help me identify the pin numbers of the 7C6 diodes. Is there some convention to identify which is #5 and #6
thanks
Elfiself

RE: A little help Please - morzh - 03-10-2018

https://www.radiomuseum.org/tubes/tube_7c6.html

This is looking at the pins.

RE: A little help Please - elfiself - 03-10-2018

Yes but which is which on the schematic itself. I don't know what to wire to which pin.

RE: A little help Please - morzh - 03-10-2018

Here's the thing: choose any diode plate of the two to be 5 and the other - 6.They are the same and it doesn't matter if you reverse them.

RE: A little help Please - elfiself - 03-10-2018

Thanks morph. This is what I suspected.
Larry