"Scott Dorsey" wrote in message
...
In article
,
boardjunkie wrote:
I have an old Eimac 450TH xmitter tube I keep around my
shop as a
conversation item (I service pro audio gear). One of my
customers who
is well versed in the mfgr of vacuum tubes says it is not
really a
great idea to have it out in the open....possibility of
radiation. Any
truth to this? He said to put it in a box with some
unexposed camera
film for a while to see if there is any radiation
activity. I've never
heard of this and the envelope is still sealed as far as I
can
tell....there's no getter in these.

Okay, there are two issues here.

First of all, when you turn the thing on, there are soft
X-rays generated
from the electrons hitting the plate. That's a serious
issue, and it's
why transmitters have some steel shielding in there.

Secondly, on a lot of tubes (and I think the 450TH is
included), there is
a little thorium on the filament to help knock electrons
off. Thorium is
an alpha emitter, and so there might be a little alpha
emission there. Not
enough to worry about, but if it really worries you stick
a roll of Tri-X
in there and see what happens.

I wouldn't open the tube up and put the filament in your
mouth, and I
wouldn't sleep it with it under your pillow, but as long
as it's not
energized it should not be a big worry.

Note that if you take a sheet of Tri-X and leave a brick
on top of it, you
will get a nice outline of the brick after about a week
due to the radiation
from unstable potassium isotopes in the brick. A pack of
cigarettes will
fog a sheet of Tri-X within about 18 hours. So compared
with other
radiation sources in the house it's not too big a deal,
and the inverse
square law is on your side anyway.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
I'm not sure how much x-ray is produced. These tubes
run at relatively low voltage for x-ray production and soft
x-rays are absorbed very quickly by air or even glass. Most
of the metal in a transmitter is shielding to prevent
radiation of radio frequencies.


--

--
Richard Knoppow
Los Angeles
WB6KBL