tube noise

[Eric Barbour]

>Yes, welcome Eric!

Thanks!

>BTW, I have been thinking about tube generated noise, has
>anyone ever investigated the neon lamp as a noise source?

There were special methods for making noise using tubes.

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.

2) Special noise-diode tubes were made by Sylvania.
The 5722 for example. 7-pin miniature tube,
plain tungsten filament, uses 1.5 amps
(filament voltage must be adjusted for best noise output).
Put 150v on the anode thru a load resistor,
and you get noise with a bandwidth of 500 MHz, allegedly.

There was also 5845, a dual diode on the same principles.
(Why dual? God knows.......)

Of course, you can get usable noise from a 10-cent zener.......
but you don't get as much fun from it! Zeners are boring,
they don't give that hot-tube Cold War feeling.......

--Eric Barbour