[Amps] 8122 x 12

[jeff millar]

That design is called a "transmission line amplifier". The tube output 
capacitance makes it very difficult to create a matched wide bandwidth 
amplifier. But, a transmission line can consist of a series of 
inductances in series and capacitors in parallel. So string a series of 
tubes with inductors daisy chaining between the plates and it makes a 
simulated transmission line with wide bandwidth. The impedance of the 
line is SQRT( L / C ), where L = inductance between tubes and C = tube 
plate capacitance. Design the line for an impedance like 200 Ohms and 
put a 4:1 impedance transformer at the output to make 50 Ohms. Play the 
same trick with the grids to form the input network.

They probably wanted to run the amplifier in pulse mode. That requires a 
lot of volts and peak amps but not much power. Pulses require a lot of 
bandwidth.

jeff, wa1hco

Chris Howard wrote:

>I dropped by the university surplus warehouse today
>and picked up a couple of beat-up RF amps, Amplifier 
>Research Model 200L.  Only one has it's RF deck, and
>that has just 11 of it's 12 8122 tubes resident.
>
>I'm a little confused though.  From what I can find
>out this guy was supposed to do 200 Watts output
>over a wide frequency range.  Why would they
>need 12 tubes?
>
>And the power supply looks pretty hefty, but
>the 8122 datasheet says 2000 volts and 300 ma
>for the plate.  Wouldn't that be (.3 X 12) 4 amps at
>2000 volts?  I don't think the primary side
>leads look like they will carry that much current.
>
>What am I missing here?
>
>Chris
>kc0atc
>
>  
>