Hi Chas
Thank you for your interesting info.
I was surprised that you mention using 400w on PSK31
I've never seen anyone mention using more than about 70w on PSK31 as
high powers are not supposed to be necessary?
Just my comment as when I experimentally tuned up my Acom 1010 amp
for 400w output I had a very irate neighbour knocking on door!
That's another story and I'm still alive hi!
Since then I've been using 5 - 20 watts cw and psk31 and having fun
73 Robert G3RCE (from the future Islamic Republic of the UK - God
help us!)
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From: Charles Greene <[EMAIL PROTECTED]>
Subject: Re: [Elecraft] Tube Linear Amp design for basic K2
To: "Wyn" <[EMAIL PROTECTED]>, <elecraft@mailman.qth.net>
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Wyn,
I have an antique Hallicrafters HT33A with a PL172 tube, and I
modified it so it will accept lower drive. Right now when I drive it
with about 20 watts from my K2/100 in PSK31, I get about 400 watts
out. That's a gain of 20 times, or 13 dB. The tube input is swamped
with a 50 ohm resistor to help in its stability. The PL172 is a
power pentode with 1000 watts plate dissipation, operated in the
class AB1 mode (no control grid current) when amplifying SSB. On CW,
it operates in the class AB2 mode, with a little higher
efficiency, A 4-1000A is the nearest new(er) design tube. I
thought about how I could make the old guy put out something exciting
when driven by my K2. I could swamp the input with a 200 ohm
resistor and use a 4:1 balun and the impedance to the K2 would still
be 50 ohms. Actually, with the K2 automatic antenna tuner, you could
tune the 400 ohms to 50 ohms. Same difference. The tube itself
does not take any power in class AB1, but the input voltage needs to
be so much for a given output. A 4:1 balun would increase the drive
voltage by a factor of 4 times which would increase the output of the
amp to 1600 watts if the drive remained the same, 800 watts with 10
watts drive, or 400 watts PSK31 with the K2 maxed out at 5 watts,
which is respectful. From 20 watts to 1600 watts is a power gain of
19 dB which in my opinion is a little high. I would be more
comfortable with a power gain of 16 dB, but you can try it.
The point is, yes you can find a tube that will take a 10 watt
transmitter to 800 watts or so, but be careful. Those tubes are
expensive.
73, Chas W1CG
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