Rickenbacher lunchpail amp circa 1934

[terminalgs]

My newest restoration project is a ca.1934 Rickenbacher "lunchpail" (pre-dates the "*backer" name change...)  tubes are old-school 2.5V filament two 47's and one 53, plus an 80 rectifier.  Here's the hand drawn schematic, I forgot  to draw the cathodes/filament connections on the 47's but the 200ohm cathode resistor is in there on the CT of the 2.5v winding..


I have measured resistances  written across the top with the layout of the board.


I fired it up with all the tubes and a light bulb limiter and the result was the light bulb took all 110V (all behind a variac to dial it down to 110),  so  removed all tubes and did the same.  This time the PT took all 110V.  I measured good voltages on the filament windings and just under 370V on the HT winding.  I put the '80' rectifier in and fired it up:  this time the amp took about 70VAC of the 110V and the light bulb took the rest.  I ran it like this for a few minutes with no change in voltages.  maybe I have some capacitor problems (they are 80+ years old!).


The choke has a weirdness to it.  It has three leads,  one has 2 20uf caps on it and nothing else, the other lead goes to the field coil.  Is this a multi-tap choke?  I wrote down the DC resistances between the input from the transformer "A", "B" (the 2 20uf caps) and "C" the F.C. 
"A-C" was about 248ohm, "A-B" was about 10ohm.


The speaker measured about 0.5ohm DC.  I know that 2ohm speakers were common back then.  I figure they'd measure ~1.2-1.5ohm DCR,  so the speaker is a question mark.  FWIW with the just the "80" installed and amp powered on, there was a VDC drop across the F.C., which I believe to be a good thing (my first pre-war amp, so there are some new things here for me to learn).




The amp is remarkably clean,  and the wiring is super tidy.   Evidently Roi Van Nest's radio shop assembled and wired these.  The speaker is a Rola and the power transformer is an "Inca".  Caps are all Cornell-Dublier.  the fuse pre-dates the 3AG style.  It's a screw in edison style (is that the right name?).




any thoughts or tips?

[PRR]

The speaker impedance is unimportant as long as the OT is OK. Keep them together.

The 3-leg choke gives a small extra filtering, _IF_ the caps are the original values. Let that be for now.

With '80 in and no other tubes, there should NOT be drop across the FC. There is no path for DC current. But really the path is through too-leaky electrolytics. At least for smoke-test, I would disconnect ALL electrolytics, tack-in good new ones.

The resistor values look rightish, not wrong. Drifted but not out of bounds, at least when cold.

When you get that far, bring up the preamp section without the power tube. Check for <1V at power tube grids (may have to wait a minute). If the grid points go high, replace the grid coupling caps.

A '53/6N7 is a very odd choice for final here. The cap-coupling will not support positive grid operation. In negative grid the '53 can only do like 5mA, which is pathetic "power". In that period, transformer coupling was still popular; any trace of that? However the circuit as drawn is a fine push-pull amp for a neg-grid power tube; I wonder if the '53 is wrong (any label or marks?). ....well, that was stupid.....