TheRadioBoard

I was browsing old issues of Popular Mechanics online, and came across this advertisement:

http://tinyurl.com/4yqz4p4

As I am currently collecting all kinds of information on low plate voltage radios, these Imp tubes attracted my attention. I was not able to find any further information on the Imp Radio Corporation, or on Prof. Kolb mentioned in the ad.

So, I decided to ask here, hoping that maybe someone can shed some light on what kind of method was used to eliminate B+ with these tubes?

Hello, this is almost certainly an early attempt to introduce the US market
to the space charge grid tube.The ads picture shows clearly the presence
of two grids.Also the short wire with connector would point to this being
the space charge grid connection.There is little literature published on
space charge grid tube operating principles.The most comprehensive
treatment is an article by Wolfgang Holtmann here:
http://www.jogis-roehrenbude.de/Radioba ... gitter.htm

Eb

Yes, good catch. I didn't count the number of electrodes in the bulb until you pointed it out. Now I'm quite certain that it's a dual grid intended to be used space charge mode.

Who is Prof. Kolb remain a mystery to me, though. And I suspect he was a fictitious character

Space charge grid tubes were developed by Schottky (Siemens) and
Langmuir in Britain independently during WWI. There was little
use in Europe,:
- Mixing in early superhets, a specialty of French superhets.
The "bigrilles" = "double grid" were the only dual-grid tubes available in 1924.
- German Reichspost (Mail &Telecom) had a amplifier
for telephone lines operated on a 4.5 Volt flashlamp battery.
- Tinkerers loved the tubes, especially boys not allowed to play
with 120 Volt B batteries (Or those were too expensive)
- Kosmos sold a educational set from 1930 on up to 1956 :
http://uv201.com/Radio_Pages/radio_technician.htm
http://www.sarganserland-walensee.ch/KO ... iomann.htm
The latter lead to some knowledge about space charge grids among German Radio
tinkerers of that age.
- some tubes for Wehrmacht, I do not know reason.
Producers of such tubes were Philips (including some affiliates)
and Telefunken.
Such tubes are in short supply today, I know of 300 DM at Ebay ten
years ago. As far as I know, production was ended mid 30ties.
And some point often understood wrongly: A space charge grid tube
is not a tube with a control grid used in a "wrong" way! The space charge
grid is a grid with special design to do "its duty".
Georg

http://www.radiomuseum.org/tubes/tube_dm30al.html
http://www.jogis-roehrenbude.de/Roehren ... oehren.htm

Some other examples here: Note - Philips "Q", 1921 ( more likely 1923)
http://www.museumoftechnology.org.uk/va ... =valves_rx