On Sep 11, 2:32*pm, (Scott Dorsey) wrote:
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."

Cool.....thats what I was thinking. THe tube hadn't been in use for 40
plus years, and I suspect it wasn't used alot since the glass is still
clear (slight green tint visable where the plate and grid connections
are) with a few small brown streaks up near the top of the plate. I
like having it around for those who think thier KT88s are "huge
beasts". Then I can go all Crocodile Dundee and point to that 450TH
and say....no, *thats* a huge tube.

I can't find it now, but some time back I saw a video somewhere on the
net of some guy that built a ~300w SE xmitter triode audio amp. The
tube was out in the open with a plexiglass shield around the front
while he stood in front of it playing a guitar through it. I got a
chuckle out of that.