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?
Thanks
--

On Sun, 4 Jan 2009, 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?
Thanks

Yes.

The first number is the voltage of the filament. Most equipment would
have tubes starting in 6 or 12, indicating 6 and 12 volts, but in some
equipment they had no transformer to drop the voltage down to filament
voltage level, so they put the filaments in series. Since there were
only a handful of tubes in the unit, they used tubes created for the
purpose, which had higher filament voltages.


The 50L6GT requires a 50volt filament, and thus uses up just under half
the AC line, making it easier to drop the rest of the voltage. It was
common to have rectifier that used 35v on the filament, which then
totals 85 and only about 30 volts more were needed. That can be
made up of 12 and 6 volt filament tubes.

By using a 30L6GT in the radio, you've caused all the other tubes
to see a higher filament voltage. At the very least, that will cause
a shortened life for the tubes.

Michael VE2BVW

"Count Floyd" wrote in message
news:BJ4mQCBKg9HM-pn2-3dWudjBJPujT@localhost...
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?
Thanks
--

Add up the tube filament voltages and see which tube is closest
to what your line voltage. I'd think that the 50L6 would be
preferable.

"Count Floyd" ha scritto nel
messaggio news:BJ4mQCBKg9HM-pn2-3dWudjBJPujT@localhost...
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?
Thanks
--

Firstly the tube that was changed by your supplier should be a 35L6 not 30L6 (to
my knowlegde the 30L6 does not exist).

Secondly the 35L6 and the 50L6 are not exactly the same tube with a different
filament voltage, As a matter of fact the 50L6 is a slightly more powerful tube,
as witnessed by its somewhat higher power dissipation and by the fact that,
despite the higher filament voltage, its filament current is the same as that of
the 35L6 (that is 0.15A). This means that the 50L6 has more cathode emission.

In any case, using a 35L6 instead of a 50L6 causes the filament voltage of all
tubes in the series string to be too high by some 10%. If you have not used your
radio with a 35L6 for a long time, I believe no damage has occurred, but it
would anywy be wise to use the original 50L6.

Regards.

Tony I0JX

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."

On Sun, 4 Jan 2009 17:27:28 UTC, "Antonio Vernucci"
wrote:

"Count Floyd" ha scritto nel
messaggio news:BJ4mQCBKg9HM-pn2-3dWudjBJPujT@localhost...
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?
Thanks
--

Firstly the tube that was changed by your supplier should be a 35L6 not 30L6 (to
my knowlegde the 30L6 does not exist).
Tony,
Thanks, it was a 35L6, a typo. Put the old 50L6 back in, it basically
was just the rectifier tube that caused the problem, so I will not
mess with what is working!
Thanks
Tony I0JX



--

On Sun, 4 Jan 2009 17:16:59 UTC, "Tio Pedro"
wrote:


"Count Floyd" wrote in message
news:BJ4mQCBKg9HM-pn2-3dWudjBJPujT@localhost...
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?
Thanks
--

Add up the tube filament voltages and see which tube is closest
to what your line voltage. I'd think that the 50L6 would be
preferable.

Tio,
Thanks for the advice. It was a 35L6, not a 30L6, but I put the 50L6
back in, it was not the problem, it was the rectifier tube, don't fix
what works, right?
Thanks

On Sun, 4 Jan 2009 17:47:42 UTC, (Scott Dorsey)
wrote:

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

Scott,
I changed the tubes just to make sure, even though it was only the old
rectifier tube that went belly up. Plus, it was 35L6GT, just a typo.
Put the 50L6GT back in, and it was still good. The replacements were
only $5, so now I have some guaranteed good spares for later.
Thanks for the reply


--

"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

On 4 Jan 2009 12:47:42 -0500, (Scott Dorsey) wrote:
The 50L6 and 30L6 tubes are variants of the classic 6L6,

I used to think that too, Scott - but look up the details some time.
They are not at all like the 6L6.