Well, I have started tearing apart my 1920's Modern Electric Mfg. battery eliminator. It is proving to be a PITA, as EVERYTHING is potted in tar. I have also had to cut some spot-welds to get things apart as well. So far, it looks like the main power transformer drives both the BH rectifier tube as well as a separate filament transformer, plus two more leads that go to a 110-volt socket on top of the case (possibly for an "A" battery trickle charger?). There is no apparent rectification of the filament power - just a plain A/C output to the binding posts marked "FIL" - might be for something like a 71A power tube in the final audio stage. Also have not identified what everything is, yet. although I have isolated (and started to melt the tar out of ) the choke/capacitor filter unit for the "B" supply. One of the cartridge resistors - the one marked "50,000 Ohms" - is still within spec, at 53K. The other two are unmarked, so I don't know how far they may have drifted, or for that matter what values I will need for my usage. I have been trying to draw a schematic as I take things apart, but it's slow going...

Hey Rich - Are you sure you need to take that unit down to bare parts? You're likely to find out the caps and choke are perfectly OK, maybe the HV transformer too.

De-potting assemblies like that is always messy and in all probability will not improve serviceability. Can't be beat as a learning experience, though!

BH rectifiers are known for their declining output with use. But at least they don't need a filament supply.

Have you been able to measure the filament output voltage (s)? That could tell you what tubes the eliminator was designed for.

No - all the wires were so badly rotted that it would have been unsafe to plug it in. I have gotten everything de-potted, and in fact the rubber rot ran right into the tar, so complete dis-assembly was definitely required. In fact, I just got done de-potting the power transformer and am letting it cool off pending further examination. Power cord needs replacing, too, and that ran right into the tar. This will be a project for certain - if it succeeds...

My next step, I think, will be to hook up a temporary power cord to the HV transformer and determine what voltages it puts out. The caps were all wax paper/foil types, and those should all be replaced as a matter of course in order to avoid excessive noise.