tube noise

[Harry Bissell]

My turn to guess... is it...is it....

The toroidal magnet produces a large local field that swamps out
external magnetic fields and makes the device insensitve to disturbances
??? (earth's magnetic field, ac hum, Roswell N.M. ???)

:^) Harry (not afraid to look ignorant when he IS ignorant...) Bissell

Doug Tymofichuk wrote:

> 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