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[AMPS] Tube IMD/6146/4cx10000

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Subject: [AMPS] Tube IMD/6146/4cx10000
From: (
Date: Sat, 20 Feb 1999 13:05:30 -0500

On Thu, 18 Feb 1999 18:09:05 -0800 (PST) igor rosky <>
>I have would also be interested in this area, my 4cx10000 has superb
>3rd order IMD. The problem is the driver,(all ham radios). My idea is
>to use  TS830s with a modified 6146, modified for improved 3rd order
>IMD to drive a 4cx600J(3rd order imd -46 db at 500 watts) then to
>drive a 4cx10000.
>My question, has anyone optimized a 6146 for best 3rd order IMD, and
>what is the typical figure. I would use solid state but typical 
>transistors have very low 3rd order IMD performance.

There are some interesting developments in SS IMD performance in the
microwave wireless industry. 
Using circuitry to sense the IMD and then phase shifting back to the
input, performance in the area of -50dB is attainable. I do not know the
details but understand it is somewhat involved.

The TS-830 is a nice xcvr Igor, I use a pair of them here on VHF/UHF to
drive transverters.
For HF you may want to add a low series R regulator to the screens of the
6146's and the 12BY7A driver. It appears that you will have more than
enough drive for the 4CX600J so consider reducing the Ep and Es on the
12BY7A primarily for longevity. 
With some fine tuning of the various voltages and currents you can expect
-40dB or better IMD under voice condx. The negative feedback used is
based upon the Collins design.

73  Carl  KM1H

>On another note i cannot measure the improved 3rd imd of the
>4cx10000J, its just as good as the plain 4cx10000. I use a HP141t, i
>might be doing something wrong in the measurment prcocess. I have
>played with numerous settings of plate/screen and grid volts, but 
>seem to get the improvement. The 4cx600J however is superb with
>bypassed cathode resistor.
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