Paper caps all replaced, and a couple out-of-tolerance cathode resistors swapped out for 1 watt carbon film. The 6F6 output stage cathode bypass electrolytic was also replaced; it wasn't in the can as specified in the schematic but was a "Dandee" brand 10uF axial lead type air-wired inside the chassis.
The paper caps were a hodge-podge of different brands - Mallory, Aerovox, Sprague, Tobe Detustchmann. The can electrolytic is an 8uF/8uF unit instead of the specified 6-6-6. Some of the paper caps weren't the correct values e.g. the 0.25uF paper cap was actually a (very large)
0.5uF unit. I'm guessing the last time this radio was serviced might have been during WW2 and perhaps wartime rationing had something to do with it - repair shop made use of whatever they had on hand.Maybe surprisingly both sections of the can electrolytic reformed OK running a current thru it via stepping up the voltage ranges while on the "leakage" setting of my Heathkit IT-11. It took about a minute for the eye to open at the rated max voltage of 450. I measure a "power factor" of around 3-4% on both sections at that voltage. Don't know if it would be good to leave that as is but I'm using it in-place for testing.
The 5Z4 and 6F6 + power supply circuit seems to be working fine, with the set powered up the voltage on the first capacitor section and the second after the field coil choke look approximately correct. Injecting1kHz into the 6F6 grid and into the grid of the 6J7 detector I get a strong output through the speaker with no hum.
The problem now is that the plate and screen voltages on the 6A8 and 6K7 are way off; the service manual specifies 195 and 210 for plate voltages respectively but I'm actually getting more like 260 and 275. The screen voltages are specified as being 70 and 90 respectively but I'm looking at about 130 for both of them. Pin 5 of the 6A8 looks correct at about
-10.5 volts. Cathode resistors and bypasses were replaced on both of them but the cathode voltages are high, e.g. with the AM broadcast band selected, volume all the way up I'm reading about 4.8 volts on the cathode of the 6A8 instead of 3.
With a 3 meter longwire antenna I'm getting one local strong AM station (50kW about 8 miles down the road) at night but the AM band is otherwise silent. I'm guessing at this point one or both of the 6A8/6K7 has poor emission? I don't own a vintage tube tester but I have both HV and low voltage bench supplies available, any suggestion on how to rig up a quick emissions test?