27 Jul
2007
27 Jul
'07
12:39 p.m.
John Foust wrote:
At 07:50 AM 7/27/2007, William Donzelli wrote:
According to the RCA receiving tube manual (1960) the getter is
Barium-magnesium alloys. An earlier reference (1933) mentions magnesium,
barium, aluminum, calcium, cerium and Misch-metal.
BTW: The U-shaped ring is a ring so that after the tube has been vacuummed &
sealed, it can be inductively heated from the outside (forms a single-winding
secondary of a transformer) to fire the getter. If you look at a variety of
tubes the getter splash is on the envelope opposite the ring, be it the top of
the envelope or somewhere on the side, and the open side of the U faces the
envelope so the getter will fire out onto the envelope rather than the
electrodes. In really old (1920s) tubes the ring was a small cup holding the
unfired getter instead.
(.. tending OT perhaps but list traffic is kind of slow .. must be summer)
The idea behind the getter is to clean up and gas
that might be
trapped in the metal elements during pumpdown. A getter is really not
to clean up gases that sneak in thru the glass metal seals - the
getters just are not that effective, and as any plumber will tell you,
leaks only get bigger.
Hmm, that reminds me of a lingering question in my mind.
As a kid, I remember harvesting tubes from dead TVs behind
the repair shop. Breaking the tube, there was often a ring
at the top, U-shaped in cross-section. I seem to remember
that they were filled with a powder that reacted with
water, fizzing. Am I mixing up this smell-memory with playing
with calcium carbide? What were common getter chemicals?
- John