"Bruce J. Richman" wrote in message
...
Robert Morein wrote:


"Robert Casey" wrote in message
...
Powell wrote:

I have Penta 12AX7A tubes. While looking for a replacements
I found these variations:
12AX7
12AX7EH
12AX7WB/7025
12AX7LP
12AX7LPS
12AX7-C

What accounts for the difference?

The "w" suffix meant that they met some mil spec, long life
or such. But realize that the military was interested on other
aspects of vacuum tubes than high fidelity audio work.

"W" stands for wolfram, which is anothe name for tungsten.
Tungsten produces a stronger filament than alloy substitutes.
LP -- low power. Filament designed for low power at the expense of
reduced
tube life.
EH -- high power variant, possibly with a stronger plate structure.
"C" -- probably modified for a minor characteristic, such as cut-off
behavior.

For Powell, I would recommend the 12AX7UYA.











Thanks, Bob. That's uiseful information for us "SS bigots" who like to
occasionally do some tube rolling in our favorite gear. But are you sure
that
those "LP" type tubes were not manufactured in the USA but barred in the
Detroit area because of threats emanating from...............?

Seriously, though, I've gone through several output tube variations wtih
my
power amplifier and always wondered about the designations. (1) GE 6550A,
(2)
Svetlana 6550C, and (3) my current matched quad of Ei KT-90 Type 3s.

I'm almost afraid to ask now, but what does "UYA" stand for?

running for cover

Bruce, we're in POLITE COMPANY here.
I would be no more inclined to explain the meaning of UYA than I would call
someone a rapist or child pornographer.
The UYA version is ideal for someone who is himself vacuous.