When I'm finishing an electronic restoration, I start procrastinating--finding unnecessary details to attend to--to defer the moment of truth: "What will happen when I power up this machine?" I still intend to build a DC power supply, but for the time being I'm going to use a store-bought battery eliminator.
I have an originally battery-operated Radiola 28 receiver-- no antenna, no speaker. It is an early model, but was produced after RCA discontinued the 877 "protective tube." It had been converted to AC with a Model 104 speaker. I have found no part numbers or values for any components except the grid leak condenser, for which the Radiotron UX199 information states, "One to five Megohms."
I have reversed the wiring changes from the AC conversion, but several components were also changed. The conversion involved replacing the rheostats for filament voltage and volume and elimination of a dual capacitor in the B+ supply circuit. I can work around the rheostat changes, but I have no clue what to use for the missing capacitors. For that matter, I don't even understand the function of the capacitors in a DC power line.
This is the best diagram I had to work from, with the missing condensers circled:
Here are the missing caps on my own diagram, on the B+ 45 and 90v lines:
So, approaching one issue at a time, I'm asking what I need for the missing condensers. I've done all the continuity testing in the chassis and the catacomb, and it seems to be okay. I checked the values of all components I could measure without opening the catacomb, and this is what I got:
If I can replace the missing condensers, or if I find that I don't need them, then I'll apply the power and start checking voltages--first without the tubes--and proceed from there.
Finally, I've reworked RCA's Radiola diagrams into something more understandable to me, and if anyone's interested, here are links to my diagrams:
'A' Voltage through chassis:
https://picasaweb.google.com/lh/phot...eat=directlink
'B' Voltage through chassis:
https://picasaweb.google.com/lh/phot...eat=directlink
'C' Voltage through chassis:
https://picasaweb.google.com/lh/phot...eat=directlink
Battery diagram through chassis:
https://picasaweb.google.com/lh/phot...eat=directlink
'A' Voltage through catacomb:
https://picasaweb.google.com/lh/phot...eat=directlink
'B' Voltage through catacomb:
https://picasaweb.google.com/lh/phot...eat=directlink
'C' Voltage through catacomb:
https://picasaweb.google.com/lh/phot...eat=directlink