No subject

simply standard tubes used at the lower voltage, and with certain dropping 
resistors (like for screen voltage) and bias adjusted to compensate for the 
lower B+.

As I remember it, there are one or two tubes only, that are specifically rated 
for low B+ on the plate. The only one I can remember right off is the audio 
output tube. There was an all solid-state module that was brought out later to 
replace that tube. It simply plugged into the same socket. 

Every other tube in that receiver is a standard tube version with simply a 24 
V filament, or is a 12 V filamented tube connected in a series-parallel 
arrangement.

Also, as I remember it, the so-called "space charge" tubes were designed 
specifically for use in automobiles at the time when tubes were giving way to 
transistors. At that time, the audio output stage was a particular problem 
since it was difficult to get adequate audio power output at 12 VDC.

However, even "space charge" tube were experimented with, and some even 
sold commercially, back in the 1920s and 1930s, but were abandoned for 
various reasons.

To reiterate: MOST of the tubes in the R-392 are NOT specifically designed 
to run only on 24 V B+. They are standard tubes. A FEW of the tubes in the 
R-392 ARE designed specifically to run on 24 VDC and may not handle 
voltages much above that. However, again, as I remember it, there are only 
two or three of those.

Looking up the tube characteristics in any of the tube manuals of the period 
will tell which those are.

However, if that receiver was mine, I wouldn't be worrying so much about 
what the tubes could handle as what certain capacitors could handle. 
Raising the B+ much above 24 VDC might blow some capacitors, or short  
out certain diodes.

Ken W7EKB