12-04-2023, 04:38 PM
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.
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.
