On Wed, 9 Apr 2008, Chuck Harris wrote:

A wrote:


If we extend the universe of tubes observed to the TV and radio types, I
would have to say that it is very rare for me to find a burned out
filament
in the 6.3 and 12V tubes. And very common in the very delicate 35-75V
tubes
used in series string sets.

-Chuck


Well, my comparable experience is the ac/dc AM/FM radios (12 v and 35 v
tubes) and in another post I mentioned buying up a number of them at a
couple of hamfests (and a thrift store) and finding that they all still
worked AND had the original tubes (marked with same brand as brand of
radio) in them.

It can happen, but probably your good luck was the result of the radio
not seeing much use. Does it show signs of obvious use?

Lots of dust, but looks mainly like there was never much moisture present.
However, I have one old Zenith with lots and lots of wear on the knobs,
loosness to the knobes-shafts, and it has all the original tubes, too.

But, by the way, I've had a lot of tube/transformer as well as ac-dc
radios and never had a tube blow out. Yeah, I know, it can be luck.
Certainly it was different with tube TV sets wev'e had where we had to
replace a tube every six onths because of brightness/constrast weakness,
or vertical/horizontal roll, etc., problems.

The 35 - 117V tubes have a large hank of zig-zagged very thin wire
as their heater. The wires come to a sharp V which isn't a good
idea. I have almost never found a 50V tube that was good.

Well, my experience was different.

But, the series string strategy was obviously the "cheap" way for
manufacturers to save on the price of a power transformer AND any
irregularities in the filament mechanical tollerance contributed to early
failure, which, of course, contributed to pressure on the consumer to buy a
whole new TV or radio, thus contributing to the nation's economy (if you
get my drift).

The AA5 tube lineup was definitely an economizing move that could only
happen in the US. At one point, GE put everything in two tubes: one
compactron,
and one rectifier/audio output tube...if I recall correctly.

Yeah, and I was a little bit against that for the reason that if you had
three functions in a tube and one blew out, you had to replace the whole
tube. Probably cheaper to manufacture, but I never looked up the prices on
the compactrons vs one/two function tubes, do you recall any?

Also, its harder to find compactron sockets and they seem smaller spacing,
so harder to repair.

FWIW, I'm phasing out of miniature tubes in favor of
octals because they are much easier to work with, solder, put VOM probes
on, and with octal keys easier to put into sockets and take out of
sockets, and I thing the glass envelope should be a little cooler since
comparable heat is dissipated over a larger surface area.

Thanks for your comments.

-Chuck