222Mhz amplifier - low cost possible solution to increase output power

Rick Beatty

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Nov 12, 2021, 11:53:12 AM11/12/21

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Hi there Pacific Northwest VHF'ers. With the increasing activity on 222Mhz SSB it came to me that a bit of power would be helpful. Looking for a solid state amplifier was pretty much not cost effective. So, upon checking the surplus market I found the Surplus of Nebraska

has a tunable 200 to 400Mhz amplifier with a pair of 4cx250K tubes in it. The price was right and one was purchased. Checking around in the junk box I found enough parts and pieces to construct a power supply that provides 1100Vdc, 300Vdc regulated, negative bias, and filament.

It was not rocket science to put this together and it only took a couple of days to complete. But it was fun.

The results are with 4 watts input, I get 150 watts output. The amp is only about 40% efficient at the lower plate voltage but it works, well.

If anyone has an extra plate transformer with something like 1000-0-1000 @.5 amps or

on I can doule to make a 1500Vdc supply at .5 amps please let me know.

Here are a couple of pictures of my military surplus amplifier

73 Rick W7RNB

Paul KD7HB

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Nov 12, 2021, 12:20:42 PM11/12/21

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Hi.

Have you been able to convert the amp to be a LINEAR amplifier?

Paul, KD7HB

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Lonney

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Nov 13, 2021, 10:22:20 AM11/13/21

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Nice work Rick, been many years since I built a tube amp for VHF (QQV 06-40A double beam tetrode, 4W in = 100W out grid driven with 600V plate voltage).

I'm from ZL, personally know Peter ZL2IK who you know, Peter also visited us when last here a few years ago now.