On Jan 1, 2012, at 5:06 PM, Eddy Swynar wrote:
Hi Garey,
Yes, a VERY good point, indeed! Thanks for adding that "PS"...
It never ceases to amaze me, whenever I'm looking for possible
"subs" in my books like that here, at just how many tubes seem to be
so very much alike---yet they have different numbers. You have to
really examine their individual specs closely, & then act
accordingly, dependent upon your specific application of the
substitute tube...
That's because most people don't understand the base concepts behind
vacuum tube numbers. RCA for example would sell a specific tube for a
function and use it in their radios and TV sets. GE would make a
similar tube to do the same thing in theirs with a different model
number. The same with Zenith and so on.
European and Japanese manufacturers used different model numbers and
numbering standards, but in the US, the substitution guides did not
show them as they were not available anyway.
TV repair people carried around, and stores, such as drug stores, etc,
had tube testers and substitution guides. The testers were very
simple, if the tube would heat up and conduct electrons it was good
and if it did not it was bad. Some testers had neon lamps that would
glow when the tube was "shorted", and most had meters, but neither
were of much use.
Many short circuit conditions did not light the lights and drug store
testers were eventually set to show that a brand new tube of the
manufacturer sold by that store showed good and all others showed
"possibly bad" or bad.
For normal use, in a radio or TV set, you could substitute a tube of
similar kind from the same manufacturer or a different number from a
different manufacturer and it would work. Maybe not as well, but most
people had no idea of what was going on inside their TV or radio and
as long as there was a picture on the screen and sound from the
speaker, no one really cared.
There were a few years when I was in high school I made pocket money
by replacing tubes in TV sets and radios. The easy way was to look for
tubes that did not glow, or were not warm and replace them. All you
needed was a 1/4 inch nut driver and a "cheater cord". Then I went to
the drug store and bought a new tube.
The difficult ones required me to got to Lafayette or Radio Shack.
Drake on the other hand did not make tubes and therefore did not make
their radios to fit their tubes, they bought tubes to fit their
radios. Therefore they actually did engineering to design their radios
(instead of combining sample circuits from manufacturers) and in some
cases need an exact replacement or changes to the circuit for a
different tube, and some adjustment when using a new tube of the same
model and manufacturer.
They also "pushed the envelope" in tube usage, using them for things
that happened to work, but they were not intended. I doubt that anyone
who designed a TV sweep tube designed them to function as a high power
30mHz amplifier, but Drake (and others) found one that did.
After all, from the point of view of building a radio using a tube
designed for RF amplification there was the 807 and the 6146. I'm not
sure of the dates, but I think that the 807 was first available in the
the 1930's and the 6146 in the 1940's.
It's just that TV sweep tubes, no matter how mistreated or misused
they would be, were cheap and available in almost any drugstore,
supermarket, hardware and department store and cheap.
Geoff.
--
Geoffrey S. Mendelson, N3OWJ/4X1GM
My high blood pressure medicine reduces my midichlorian count. :-(
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