[Amps] 8122 x 12
avilaseca at bluewin.ch
Wed Dec 29 01:52:04 EST 2004
How could such an amp be converted for shortwave use?
Can it be assumed that a broadband 4:1 transformer (ferrite toroid core)
at the output is all what it takes to get it running on the shortwave
bands? A no-tune linear from 160 m to 10 m or even higher?
Angel Vilaseca HB9SLV
jeff millar wrote:
> 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
> 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?
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