Good info Bob. I understand from a few forums that a new Sibley book is
ready for release. Is this true? Id rather wait than buy an outdated
version.
In the same vein do you know the introduction date of the 247 ? Im trying
to date a superhet console radio that appears in no literature or is known
by several large collectors. The 247 appears to be the newest tube in the
lineup. The radio faceplate says Little Giant and the label on the chassis
is gone. With Meissner black wrinkle IF cans its obviously assembled from
catalog parts. Some suggest it is a bootleg from a small independent to
evade the RCA licensing. Build a small run, sell to a store and then move on
and keep doing it.
Tube line up is (2) 24A, (2) 235, (2) 227, 247, 280 and a pair of 2 pin 3L's
on a sub chassis which Im guessing are mercury vapor ballasts? The sockets
are marked Amperite.
My guesstimate is that it was built in1932-33.
Carl
KM1H
----- Original Message -----
From: "Bob Deuel" <[EMAIL PROTECTED]>
To: <amradio@mailman.qth.net>
Sent: Thursday, February 14, 2008 6:12 PM
Subject: [AMRadio] Re: 6V6 vs 6L6
I agree that substituting a 6V6 for a 6L6 is quite a stretch. I am an
active and founding member of the Tube Collectors Association, Inc. Over
the years the topic of tube substitution guides has been discussed within
our group. The general consensus is that there are numerous "tube
substitution stretches" and downright misinformation in the literature.
Sometimes it is just a simple alpha transposition such as 6AC7 v.s. 6CA7
(there is a big difference between those two tubes) and other times the
recommended substitution totally incompatible. It is interesting to compare
recommended tube substitutions by various authors and see how the authors
differ in their substitution findings. In my opinion, a tube substitution
guide is a valuable resource in "homing in" on possible replacements and no
more than that. One should then review the published tube specifications of
the intended replacement tube and determine its compatibility before making
the substitution.
While on the subject, as the demand for tubes waned and production
decreased, manufacturers resorted to creative substitutions so they would
not have to tool up for a particular tube. Here are some examples I have
in my collection: a 6SQ7GT (octal based duodiode-triode) that obviously
has the internal elements of a 7-pin miniature 6AV6 (duodiode-triode)
complete with the mica wafers designed for a 7-pin miniature glass
envelope. I also have a Sylvania 6J5GT (octal based medium mu triode) that
has the internal structure of a 6SN7GT (octal based twin medium mu
triodes). Only one of the twin triode sections is used and connected to
the base in the 6J5GT configutation. The other triode section just sits
there supporting the mica wafers and totally unconnected. More unusual, is
a Sylvania 6SF5 (metal shell octal based triode). Inside the metal shell
is a a 7-pin miniature 6AV6 (duodiode-triode) complete with a 7-pin
miniature socket! The extra non-needed and unused duodiode elements of the
6AV6 are strapped to the cathode. What made this tube suspicious was the
tall metal shell normally found on a metal 6V6. Another unusual one is a
metal RCA 12SK7 that has inside it a 7-pin miniature tube which is assumed
to be a unmarked 12BA6. Also interesting is that the 12BA6 tube has the
four creases on the top of the glass envelope that is common to European
tubes! So you can see the "big boy" manufacturers were scrambling to
supply various tubes towards the end of the US tube manufacturing era.
It is also interesting to note the industry's blatant mis-marking and
deceptive production of various tubes. Jim Cross has on this web-site
www.vacuumtubesinc.com a link that he authored and calls "Vacuum Tubes,
Inc., Hall of Shame". There he identifies various tubes that are "Marked
with the Intent to Deceive", "Marked as a Suitable Substitution" and
"Friday at the Tube Factory". His site is worth looking at. For those of
you that seriously work tubes, there is a great reference book for both
users and collectors alike called "Tube Lore" by Ludwell Sibley. I know
Vacuum Tubes Inc. has that book available.
Bob, K2GLO
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