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.

"boardjunkie" wrote in message
...
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.

This rings a vague bell. The filiments used in this
tube, and very many other tubes is thoriated tungsten.
Thorium, in some forms, is radioactive. I don't know how
much thorium is in the filiments but I suspect not much. BTW
some lenses made shortly after the development of rare-earth
optical glass contain some thorium and are radioactive
enough to require some care. These are mostly some WW-2
vintage aerial photo lenses. Thorium glass has some
desirable optical properties but is eventually stained brown
by the radiation. There is a bit on these lenses on the web,
do a google search for radioactive lenses.


--

--
Richard Knoppow
Los Angeles
WB6KBL

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."

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.

boardjunkie writes:
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.

There's a group making SE triode amps out of 833As ... could be the
same one ... http://www.wavac-audio.jp/he833v13_e.html

"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