Of course, towards the end of the life of tubes, one could get some that
ran off 12v, intended for use in car radios. *Not so useful now since they
were produced in a limited time span as transistors were taking over, so
quantity is relatively limited.

The R392 ran off 24 or 28 volts, using those low plate voltage tubes. *Of
course, it had a lot of tubes so the filament drain was large.

Of course, some people experimented with low voltage on regular tubes. *A
loss of gain, but sometimes that was a good thing.



The R392 used conventional tubes selected for performance at 24 volt B
+. 24 volts isn't much but is a lot better than 12. The 12 volt tubes
were space chrge affairs and were current hogs and delicate.