"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

In article ,
Bill M wrote:
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.

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.

I pulled out the HB-3 for this and wow... it sure IS different. Only
8.5 watts dissipation, versus 14 for even the baby 6V6.

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.

According to the HB-3, the 25L6 has ten watts which is a bit more than the
50L6. Mine does not have a page for the 35L6 but there is a note saying
the 35B5 is an equivalent.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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.