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Re: Tube coil ideas using 600W tetrodes?
Jim,
I shy away from employing tetrodes in high powered Tesla coil service
because they are just too much trouble. It is very easy to melt the screen
grids out of them in a tuning accident. I stick with triodes almost
exclusively. Besides having to fabricate an extra screen grid supply, you
really should provide a means of detecting oscillator load variations in
some sort of a feedback path to correct the screen voltage and therefore
the SOA of the tetrodes. As you are aware, Tesla coils are certainly a
extreme example of an RF power source subject to wild load variations.
If your desire is to make a *BIG* vac toob TC, call around your local AM
and FM radio stations and try to make buddies with someone in their
engineering staff. You might be able to obtain a 3CX10,000D or better a
3CX10,000A7 (flying fil. leads) as a serviceable 'pull'. Such a tube can
make a pole pig work for its reputation.
I have built a unit employing three EEV BR1160 (5 kw dissipation each)
triodes in parallel that can source lots-o-RF watts in the 80-120 KHz
region. This machine is affectionately called the ''Coronatron'. Tube
biasing was easy!
Vac toob TC's is one area where one should follow the KITS principle. Keep
It Triodes S........!
These ideas represent merely my own opinion. Flames from overheated pole
pigs driving vac toob powered (any flavor) Tesla coils welcomed!
Robert W. Stephens
Director
AREA31 Research Facility
www.area31-dot-org
----- Original Message -----
From: Tesla List
To: tesla-at-pupman-dot-com
Sent: Thursday, February 10, 2000 20:24
Subject: Tube coil ideas using 600W tetrodes?
Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
I have just come into a set of 4 4CX600J (600W plate diss Tetrodes, good to
110MHz), and what's more, all the hardware (chimneys, sockets, etc.), power
supply parts, cooling plenums and fans, (the stuff that takes forever to
fabricate and a fortune to buy) (The 4CX600J/8809 is a low voltage, high
current tetrode specifically designed for exceptionally low intermodulation
distortion and low grid interception... from Eimac catalog:
http://www.eimac-dot-com/catalog/16384.htm )
Now these little puppies put out about a kW in RF amp service and around 1.9
kW running Class AB as an AF amp or modulator. So there is some real
potential here to build a big tube coil (5-10 kW peak?)..
The question is, is this a good use for these tubes, or should I use these
to build a big HF linear amp (Take that, pesky neighbor) and get some other
lower frequency tubes for coiling... After all, it seems a waste to run a
100 MHz capable tube at 100 kHz..
Jim Lux
phone:818/354-2075 fax:818/393-6875
Spacecraft Telecommunications Equipment Section
Jet Propulsion Laboratory M/S 161-213
4800 Oak Grove
Pasadena CA 91109