[Amps] 8122 x 12

[Karl-Arne Markström]

About 30 years ago, you could buy such an amplifier from Marconi, the H-1000.
It used 12 4CX250B's in a distributed wide-band amplifier configuration and provided
1 kW CW or PEP with 100 mW drive between 1.5 and 30 MHz. 

The major use for these amplifiers were in Navy tactical HF and countermeasures.
As I remember them, they were a maintenance problem, as tube ageing always shifted
the operating points around.

There may still be some of these around in Naval installations somewhere.

73/

Karl-Arne
SM0AOM


----- Original Message ----- 
From: "Angel Vilaseca" <avilaseca at bluewin.ch>
To: "jeff millar" <wa1hco at adelphia.net>
Cc: <amps at contesting.com>
Sent: Wednesday, December 29, 2004 7:52 AM
Subject: Re: [Amps] 8122 x 12


> 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
> > 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
> > >
> > >
> > >
> > 
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