After a total re-cap, re-building the bleeder resistor strip, undoing old mods, and realigning this receiver, it plays very well now. However the metallic 5Z4 full wave rectifier tube seems to run extremely hot to the touch after a few minutes. Is this normal? Power source is limited to 115v as per spec for this radio.

Hi Steve,
That metal 5Z4 will probably run hot enough to burn the paint right off of it.
One thing to check: make sure your input filter cap is rated close to what is called out in the schematic. A higher value is ok but it probably shouldn't be higher than about 25Mfd.
BR,
Dave KC8RKC

Thanks Dave. The schematic calls for 16 mfd on one side of the speaker field and 30 mfd on the other. I used new can electrolytics with 20 mfd and 30 mfd respectively. An old repair job had 30 mfd on both sides, but I thought something closer to the original specs were better. I won't worry about it then. thanks

:Hi Steve,
:That metal 5Z4 will probably run hot enough to burn the paint right off of it.
:One thing to check: make sure your input filter cap is rated close to what is called out in the schematic. A higher value is ok but it probably shouldn't be higher than about 25Mfd.
:BR,
:Dave KC8RKC
:
:

Dave's correct - the rectifier tube always runs hot.

Larger filter caps increase the B+ inrush surge, and therefore causes wear and tear on the rectifier for a few seconds at power turn on. But, I don't think oversized filter caps will cause extra stress or termperature on the rectifier after it's warmed up and at steady state.