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Noob, looking for help restoring Philco 37-620 - Printable Version

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Noob, looking for help restoring Philco 37-620 - JLuke - 03-15-2021

Hi All,

I have recapped and finally got a couple of stations on my 37-620 chassis. The volume is low. When I touch the grid of the RF or Detector, the volume increases  and the noise  also increases. I think the AVC is not functioning properly. The schematic is attached. Hopefully someone can point out the AVC circuit.

Thanks

Jim

RE: Noob, looking for help restoring Philco 37-620 - morzh - 03-15-2021

Check the continuity of your RF coils in front of the 1st RF OR the actual connection to the Grid of it.

RE: Noob, looking for help restoring Philco 37-620 - OZ4 - 03-15-2021

I second what morzh said. There are things I would think more likely than the AVC. Dirty contacts with all those switches in the front end for starters.  Did you check the continuity of the coils? Did you test the tubes?

RE: Noob, looking for help restoring Philco 37-620 - JLuke - 03-15-2021

Hi All,

Thanks for the replies. sprayed and rotated switches.. seems ok. I measured 51.9K, from the grid of RF to the grid of Osc. Primary has continuity, so I think that there is continuity through the secondary of the AM coils.

RE: Noob, looking for help restoring Philco 37-620 - OZ4 - 03-15-2021

It sounds like there is enough gain. So it seems likely the antenna transformer is not working well. 

Poke around there and see if you can find something wrong. Try the antenna wire on the grid of the RF.
You should get lots of noise or maybe even be able to tune in a station.

As to your original question the AVC line at the band switches is where the b line and the d line come together through R6

RE: Noob, looking for help restoring Philco 37-620 - morzh - 03-15-2021

1. Put your Ohm-meter between "Black" and "Red" wire terminals on the outside Antenna screw terminal.

At any position of the band switch there should be continuity (almost short) between the two and any of this and the GND (terms 1,2 and 3).

2. At the input transformers secondaries, between any of theirs pins 4 and 5 there should be continuity to the RF Grid.

RE: Noob, looking for help restoring Philco 37-620 - JLuke - 03-16-2021

Hi All,

The continuity from red to black is almost  zero ( 1.5-2 ohms). Touching the grid of the RF does allow, very noisy, connection to a station. Touching the outside of the antenna coil does the sam. Connecting a an antenna or touching with a finger to Red does nothing.

RE: Noob, looking for help restoring Philco 37-620 - OZ4 - 03-16-2021

Sounds like something is killing the signal right at the transformer. Does that ground jumper have any effect?.

With the ground jumper connected there are two paths for the signal on ether side of the grounded center tap. (red or black)

Connecting to the ether side of the primary does that have any effect? 

This maybe a dumb question. You have tried switching the bands while testing?

RE: Noob, looking for help restoring Philco 37-620 - morzh - 03-16-2021

Luke,

what about the point 2 in my post?