Tokyo High Power had a nice compact 2x 4X150/250 amp that was Super Cathode
driven. Ive repaired a few but didnt have the equipment at home then to run
IMD tests.
The NCL-2000 may have been the first commercial linear (1963) to use a 50
Ohm swamped grid input. In that tap position it would do 1200W out key down
with 15-20W drive.
Carl
KM1H
----- Original Message -----
From: "LA7SL Nils Petter" <la7sl@norgespost.no>
To: <amps@contesting.com>
Sent: Friday, April 01, 2011 2:16 PM
Subject: Re: [Amps] 813 Amplifier Article
>I ran 2x 4cx250B grid driven with passive grid in AB2.
> Grids loaded by 50ohms dummy load and bias feed on
> "inside" of grid coupling C via RFC (could have coupled
> bias to ground side of dummy R but then I would have
> needed a real RF bypass cap there to handle the drive power.
> I got away with a regular 200V disc :-)
> G2 fed with normal voltage and bypassed to ground. I got into trouble
> with my first screen supply as those tubes draw negative G2 current
> over part of operating range. That solved ,-this little amp performed
> flawlessly more than three years. The driver was a FT901 (tuned output)
> so the IMD was not too bad. Pwr out was in the range 650 watts. The amp
> was a monoband 75 meters job. Worked a lot of good DX phone on it !!
> Telling this just to show that it does not take much to get a respectable
> signal, not much work or professional skill either really.
> My next project was a very similar thing, just BIGGER :-) using
> QBL5-3500's
> Those are 3KW plate diss jobs... and tuned grids this time,- but that is a
> different
> story...nearly burned down my barn on the farm here.... too tight coupling
> to
> something apparently :-) Did not work much more DX on that one, I just
> did
> not
> have to spend the same amount of time in the pileups....
> Now I am 61 and have become an appliance operator...
> Peter
> ----- Original Message -----
> From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
> To: "Rob Atkinson" <ranchorobbo@gmail.com>; "Carl" <km1h@jeremy.mv.com>
> Cc: <amps@contesting.com>
> Sent: Friday, April 01, 2011 7:28 PM
> Subject: Re: [Amps] 813 Amplifier Article
>
>
>>I once knew a guy in Nashville, John Brown, who loved building amplifiers
>>in the 1960's.
>> He made a RF deck that he drove with his TR3 or TR4 which he could change
>> sockets and
>> try different tubes that most people would not try or had be advised not
>> to try.
>> One setup was four 4-65As in grounded grid. Talk about hot plates when
>> he
>> pushed up the plate input power. They were a bright yellow
>> Another set up was 4x 4CX250bs or were they 4X150A/7034? No difference
>> really.
>> He tried direct grounded grid, they were toasted. Then connected the g1
>> to k and low
>> power gain but worked well and lastly he tried g1 to ground via a
>> resistor
>> to limit grid dissipation.
>> None worked out to his satisfaction.
>> 73
>> Bill wa4lav
>>
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