tube noise

[Doug Tymofichuk]

On Wed, 8 Dec 1999 12:19:17 -0800 Eric Barbour 
<svetengr at earthlink.net> wrote:

> 1) John Atwood has a General Radio "Broadband Noise Source"
> from the 1950s. It contains a 6D4 thyratron, biased to be 
> conducting all the time, and with a large donut-shape 
> alnico magnet surrounding the tube.
> (anyone care to guess why?....) The gas noise appearing on 
> the plate is then amplified with a 12AT7 preamp. Works very 
> well--John says he tested it on the bench, and got a 
> fairly flat white noise spectrum out to >10 MHz.

O.K., I frequently work with high power magnetrons in 
linear accelerators, and I have a basic idea of theory of 
operation. Could the magnetic flux be doing similar things 
inside the thyratron, curving the path of electrons so that 
they strike the anode in a more random pattern? 

Or is it to better focus the electrons onto the anode? Or 
maybe to change the frequency spectrum of the noise to some 
degree by speeding up or slowing down current flow? All of 
this depends on the internal geometry of the thyratron, and 
mine is at home, so I can't check it now. Is this the type 
with the cathode vertical in the centre and the grid and 
anode wrapped around it, so that the electron flow is in 
the horizontal plane?

I just happen to have a 6D4 in my tube box, and a donut 
shaped magnet from a woofer, so I should give this a try. 
Is there a schematic available anywhere, or is it just a 
standard circuit configuration?
 
I'm still interested in trying to get noise from neons, 
however. Wouldn't you get some degree of gas noise from any 
gas-filled tube?
----------------------
Doug Tymofichuk
dougt at cancerboard.ab.ca