[artbev]

I've got a two-45 tube model 90 on the bench. The owner had tried to restore the chassis but created a huge mess - instead of restuffing bakelite cap blocks he just added external caps (all wrong value parts) most of which are hanging from tails of wires. I've got this all straightened out at this point.

My question now is regarding the volume control. There are two sections, one passes a variable amount of antenna to the grid of the RF tube, (via coil #2), and the other straddles "F" and "G" points on the power resistor and controls voltage to the cathodes of two of the 24 tubes.

One of my schematics shows one section to be 5k ohms and the other 250 ohms.

It appears that the prior person flipped the wiring between the two sections, F and G are wired to the 5K section (with the wiper grounded which makes no sense) and the antenna is wired to the 250 ohm section. 

Based upon the schematic that I have with resistance values the current arrangement is backwards.

Can anyone confirm this? (The attached picture has some wires disconnected as I was measuring the sections. You can see that there are two pins grounded, which also doesn't match the schematics)

Thanks very much.

[Radioroslyn]

Hi and welcome to the Phorum,

Here's a couple of things that may make it easier to work on.

https://philcoradio.com/library/images/schem/90a.jpg

https://philcoradio.com/library/download...n%2056.pdf

Methinks you are correct that the two sections are switched, the 5k should be controlling the ant section and the 250 ohm section controls the bias on the rf/if tubes.

GL w/your project! I'm working on a early model 70 which uses the same setup.

[klondike98]

Welcome to the Phorum!

[GarySP]

Welcome Artbev! Looking forward to your posts on your progress. Take care and BE HEALTHY! Gary

[artbev]

Thanks everyone for the responses to the volume control question. I rewired it to match the schematic. I also cleaned up the bird's nest created by the owner many years ago. He had hollowed out some of the bakelite cap blocks and used them as terminal strips, others cap blocks were removed and new caps wired unsupported in midair, most were the wrong values.

Finally the cabinet was cleeaned up with a refreshed finish and new grille cloth.

The radio works extremely well, the owner's daughter arranged this repair for her now elderly father (the owner) and she is verry happy and excited to give this to dad for Christmas.

[klondike98]

Nice work!