"Scott Dorsey" wrote in message
...
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."

The 50L6 is NOT a relative of the 6L6. It is a pentode
power tube with 10 watts of plate dissipation compared to 19
watts for a 6L6. The 6L6 puts out about 2.5 times the power
when operating as a single tube Class-1A aplifier. Other
characteristics are also different.
The 50L6 was intended for use in AC/DC "5-tube wonder"
receivers usually with a 35Z5 rectifier and three 12 volt
tubes for the remainder for a filiment drop of 121 volts.
There are equivalent (but not identical) miniature tubes to
serve the same functions. There are also some lower voltage
heater rectifier and power output tubes for use in AC/DC
receivers with additional stages. Actually some fairly
advanced AC/DC receivers were made, for instance, the
National NC-45 and NC-46 , which are 9 tube AC/DC receivers
with two IF stages and push-pull output. Both have series
string heaters with a total drop of about 120 volts.


--

--
Richard Knoppow
Los Angeles
WB6KBL