"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