[Amps] 8122 x 12

[Angel Vilaseca]

I made a search with Google and I found the Amplifier research Model
200L mentioned in a text about an experimental plasma generator.

G3rzp at aol.com wrote:
 
> I've got some papers from an IEE Conference on HF back in 63, where they
> were described. There'a also a paper from STC about a 60kW tx: 

Could you please make some info available?

> I don't think there's anybody left making fair sized HF tx's in the UK -
> well, maybe some of the UK subscribers to this reflector!

I am currently building a two 4CX250B shortwave linear. But I also do
have one 10 x 4CX250B transmission line amplifier I found at the CERN
surplus some years ago. No name or data printed on it. Until yesterday I
had never heard about transmission line amps and I had no idea what kind
of circuit this was. Maybe I will be able to use it at last.

In my amp, the ten 4CX250Bs are wired in pairs, the plates of each pair
are linked by thick ( 3 mm dia) wire inductors, with inner dia. about 10
mm. The inductors have a different number ( 3 to 5 ) of windings when
going from one end of the amp to the other. Which end should be
connected to the RF output and which one to the loading resistor? Also,
do the small inductances mean that the amp was intended for above 30 MHz
operation?

Of course, wasting half of the output power in a resistor is not very
satisfying. What if I replaced all of the inductors with a wide copper
strip and used the amp as a 10x parallel 4CX250B, with a classical tuned
switchable multiband input and output circuits?

Instead of wiring the output (and input) at the original end of the row
of tube pairs, I could re-wire it halfway between. The pairs ot tubes
furthest from the output would then be about 20 cm away from it. That is
2% of the wavelength on 10 meters. Would this cause problems, or would
it be beneficial, like making the amp more broadband?

The output capacitance would be very large, but maybe the amp could be
used at least up to the 20 m band?

What kind of power can I expect to produce in narrowband mode? Why not
10 x 250 W? Of course, I would throttle it back to 1000 W, the max.
legal output here in Switzerland, or less, to avoid the usual
"collateral damages". But this would give a very comfortable safety
margin.


I love this reflector. I learn at least one new thing every day with it.
Thanks to all posters!


Angel Vilaseca HB9SLV