Count Floyd wrote:
Just changed some tubes in my S-38 and the original 50L6GT was changed
to 30L6GT by my tube supplier. I know that it is the audio output
tube, but listening to it does not seem to make any difference. Is
there a difference? Should I pull the tube and use the 50?

With American tubes, the numbers at the beginning are the filament voltage,
the numbers at the end indicate the number of elements in the tube, and
the letters in the middle are more or less random.

The 50L6 and 30L6 tubes are variants of the classic 6L6, built with higher
voltage filaments for series string radios. If you put a 30L6 in place
of a 50L6, not only will it fail prematurely from the high filament
voltage, but so will all the other tubes in the radio because they will
also be seeing high filament voltages.

You _can_ make it work by increasing the value of the series resistor
on the filament string to make sure all the tubes are seeing the correct
filament voltages. If you do this, write a note inside the case warning
future users of the equipment about the modification.

Why did you change the tubes in the first place? The old ones are
probably all fine anyway.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."