"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

Richard Knoppow wrote:
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.

Yeesh! That is not good at all! That is a very misleading number in
that case.

What about the 25L6 then? I have pitched a lot of 25L6 tubes
over the years because they showed low transconductance compared with a 6L6.
--scott


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

"Scott Dorsey" wrote in message
...
Richard Knoppow wrote:
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.

Yeesh! That is not good at all! That is a very
misleading number in
that case.

What about the 25L6 then? I have pitched a lot of 25L6
tubes
over the years because they showed low transconductance
compared with a 6L6.
--scott

Its identical to the 50L6 except for the heater voltage
and current.
The numbering system for tubes was intended to be
systematic but broke down pretty quickly because of the
plethora of new tubes. The earliest system was chaotic with
numbers but also prefix letters usually indicating the
manufacturer. For instance, RCA prefixed its tubes with UX
so a UX-210 is a 210 tube made by RCA but others also varied
the numbers, I think DeForest used 5 in place of 2 so a
Deforest 210 became a 510. The number-letter-number system
began sometime around the early to mid 1930's. I used to
know the exact date but its evaporated. Note that while the
first number usually indicates the filament voltage that is
not always true. For instance, Philco and others made
"locktal" tubes, a variation of the octal type but with
plain wire leads and a sort of locking base. These usually
have a 7 as the prefix of the type number but mostly have
6.3V filaments. As usual in life chaos reigns supreme.


--

--
Richard Knoppow
Los Angeles
WB6KBL

Other two cases of inconsistency:

- the old 814 made by Taylor is a transmitting triode, whilst the 814 we all
know is a power tetrode.

- the 6BN8 is a noval twin diode - triode. But there also is an octal 6BN8 which
is a twin-diode pentode.

73

Tony I0JX

On Mon, 05 Jan 2009 09:54:36 -0500, Scott Dorsey wrote:

Richard Knoppow wrote:
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.

Yeesh! That is not good at all! That is a very misleading number in
that case.

What about the 25L6 then? I have pitched a lot of 25L6 tubes over the
years because they showed low transconductance compared with a 6L6.
--scott

AFAIK the numbering -- other than the filament voltage, and other than
suffix letters -- is almost completely arbitrary; any similarities in
functions between similarly numbered tubes in a marketing, rather than an
engineering, decision.

Even then, as Richard pointed out, the filament voltage sometimes isn't,
and a 'G' variant of a metal tube often has different interelectrode
capacitances than the parent tube or the 'GT' variant.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Scott Dorsey wrote:
Richard Knoppow wrote:
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.

Yeesh! That is not good at all! That is a very misleading number in
that case.

What about the 25L6 then? I have pitched a lot of 25L6 tubes
over the years because they showed low transconductance compared with a 6L6.
--scott


Personal opinion of mine...I think the * manufacturers* intended a
35/50L6 to be a DESIGN replacement for the old 6L6 as applied to AA5
50s-60s radios. Walks the same walk but its a 150 volt tube.

No question about it....its not very closely related if you're looking
from a conventional 6L6 perspective. 25L6 is sort of a different animal
not related to either of the two.


-ex

"Bill M" wrote in message
...
Scott Dorsey wrote:
Richard Knoppow wrote:
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.

Yeesh! That is not good at all! That is a very
misleading number in
that case.

What about the 25L6 then? I have pitched a lot of 25L6
tubes
over the years because they showed low transconductance
compared with a 6L6.
--scott


Personal opinion of mine...I think the * manufacturers*
intended a 35/50L6 to be a DESIGN replacement for the old
6L6 as applied to AA5 50s-60s radios. Walks the same walk
but its a 150 volt tube.

No question about it....its not very closely related if
you're looking from a conventional 6L6 perspective. 25L6
is sort of a different animal not related to either of the
two.


-ex

The characteristics of the 50L6 are so completely
different from a 6L6 that its obvious that it was a
purpose-designed tube. About the only similarity is the use
of beam-forming plates to get higher efficiency than is
possible using a conventional pentode. This design
originated about the mid 1930's. I am not sure which tube
employed it first, perhaps the 807. In some ways the 6l6 can
be viewed as a single-ended version of the 807 although
there are some differences other than construction.
Also, most of the early octal-based tubes were derived
from previously available large pin base tubes. I am not
sure about the 50L6 although there were high-voltage heater
types available previous to the octal base intended for
similar applications, i.e., AC/DC receivers.
According to the _RCA Receiving Tube Manual_ edition
RC-19, the 25L6 is identical to the 50L6 except for the
heater rating.
There were modified versions of the 6L6: the original
was a metal-shell tube but was followed by the 6L6G which
originaly had a large partly pear-shaped envelope, this was
followed some years later by the GA, GB, and GC versions.
The GA has a low-loss base but there are other changes in
the latter versions, mainly increases in screen grid
dissipation. The GC is essentially the same tube as the
5881. This tube was intended for service in circuits such as
the "ultralinear" audio amplifier where the screens are
operated at the same potential as the plates, a condition
which will cause short life in a standard 6L6.
The manufacture of tubes is fascinating and much more
complex than appears on the surface requiring the services
of many specialists such as metalurgists, glass specialists,
etc.
There are two internal RCA training manuals about tube
design and manufacture on Pete Millett's web site at:
http://www.pmillett.com/tecnical_books_online.htm
Which also has a great deal of other stuff of interest
to boatanchor types including the 4th edition of the
_Radiotron Designer's Handbook_.


--

--
Richard Knoppow
Los Angeles
WB6KBL

Richard Knoppow wrote:

The characteristics of the 50L6 are so completely
different from a 6L6

Thank you.

"Bill M" wrote in message
...
Richard Knoppow wrote:

The characteristics of the 50L6 are so completely
different from a 6L6

Thank you.
You're welcome:-)

FWIW, here are some common combinations of tubes used
in 5-tube AC/DC sets. These were typical but its not an
exaustive list, there were other tubes designed for series
string operation directly from the power line. In England
and in Germany other tube types were designed for the same
purposebut operating from 230/250 volt mains. In fact the
famous and rare original tube used in the famous
Telefunken/Neumann U-47 was originally intended for such
use. It was chosen because the filament could be run off the
microphone bias voltage, an economy move since it
elmininated the need for a separate DC filament supply:

C.1934, from the RCA RC-12 tube handbook:

6A7 Converter
78 Remote cut-off IF amplifier
77 Combination dual diode and triode (detector, AVC,
first audio)
43 Audio output
25Z5 Rectifier
Plus 150 ohm, 10 watt filament dropping resistor

From the RCA tube handbook RC-19 (1959)
Miniature tube types

12BE6 Converter
12BA6 Remote cut-off IF amplifier
12AV6 Combination dual diode-triode (second
detector-AVC-first audio)
50C5 Audio output
35W4 Rectifier

Two other examples:

Hallicrafters S-38B, a five tube set typical of many of the
early 1950s.

12SA7 Converter
12SK7 Remote cut-off IF amplifier/BFO
12SQ7 Combination dual diode-triode (second detector, AVC,
first audio)
50L6 Audio output
35Z5 Rectifier

The original S-38 was a six tube set with an additional
12SQ7 tube as BFO and noise limiter. In the S-38B the BFO
was obtained by allowing the IF stage to regenerate, a
circuit patented by Hallicrafters and the ANL was
eliminated. I am including the S-38 because it is an
application of the 35L6.

S-38 (c. 1949)

12SA7 Converter
12SK7 Remote cut-off IF amplifier
12SQ7, No.1 Combination dual diode-triode (second detector,
AVC, first audio)
12SQ7, No.2, BFO and Automatic Noise Limiter
35L6 Audio output
35Z5 Rectifier

Note that the filament drop here is 118V and in the five
tube circuit its 121 volts, all close enough to the 110V to
120V range for AC current at the time these sets were in
use. DC voltage was common in some cities, notably New York,
I think at around 110 volts. DC was convenient for operating
traction motors of the sort used in elevators so it was
continued until a surprizingly late date. DC was also
available in some other US cities but its beyond my recall
which ones. 110 VDC was also common on shipboard.


--

--
Richard Knoppow
Los Angeles
WB6KBL

.. DC voltage was common in some cities, notably New York,
I think at around 110 volts. DC was convenient for operating
traction motors of the sort used in elevators so it was
continued until a surprizingly late date. DC was also
available in some other US cities but its beyond my recall
which ones. 110 VDC was also common on shipboard.

Richard Knoppow
Los Angeles
WB6KBL

110VDC on ships, Oh yes! Partner and I repairing radar
on one such ship, bravely plugged in our trusty Weller
soldering gun and pulled the trigger. Nothing for a few
seconds, and then a little curl of smoke. When trigger
was released, it hissed, breathing fire and sparks out of ALL
the air cooling vent slots. Throwing it on the deck and
stomping on it only aggravated the fireworks. Stone
faced Skipper calmly pulled plug from wall, and I think
he lost some admiration of our technical competence.
Old Chief Lynn, W7LTQ