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Old 10th Nov 2018, 8:25 pm   #1
G4YVM David
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Default Amateur radio HF linear amp

Looking for a linear, any age or type, project really with a positive chance of success. Whatever you might have...

David
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Old 10th Nov 2018, 8:32 pm   #2
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Default Re: Amateur tadio HF linear amp

I built one of these and it works really well: http://hfsignals.blogspot.com/p/25-w...40-and-20.html
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Old 11th Nov 2018, 12:41 pm   #3
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Default Re: Amateur radio HF linear amp

David,

as long as you are comfortable with valves and some potentially lethal voltages (2,500V for instance) then the old 813 or 2 x 813 types are both common and easy to get working. The danger is of course that you kill yourself before you can see it working.......just joking! (But great care is essential).

There should be lots of those old linears about - in the usual places. Maybe someone here will have one which is unwanted.

Otherwise you could DIY from scratch. And not necessarily with valves - Mr Bungle's offering looks excellent, though you may want a lot more power than 25W of course.

If its vintage you are after, then there are some interesting early military ones. The well known "Amplifier RF No.2" which boosted the WS19 to sensible levels is one - but now hard to find and very pricey - that had 2 x 807s or 4 x 807s in it. The little known LV-80, used to boost the Nato GRC-9 HF manpack is a very nice small unit - I think the valve in it was a 6146 or similar. And if you want to be totally ridiculous, there is a huge valve unit which came as the high power RF deck of the D11 SSB transmitter used by the British Army - a solid 400W output no problem (provided you have a power supply man enough for the job!) - I might be able to find you a spare one if that tempts you.

Richard
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Old 11th Nov 2018, 12:53 pm   #4
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Default Re: Amateur radio HF linear amp

You could also keep an eye open for an Ex R140 Soviet amplifier - All bands HF, from 1.5 to 30Mhz, and subject to power supplies, very comfortable at 26dbW.

F1FRV has conversion instructions on his website, and eBay seller DL6CHD usually has an RF deck or two floating around.
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Old 11th Nov 2018, 2:22 pm   #5
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Default Re: Amateur radio HF linear amp

Thanks all.

Im looking at puttingnup my 15watts to around 200 if possible. Ive never used a linear, so its more out of interest.

Im happy with valves...repaired a few old 101s in my day. I think ive actually got one or two 813s..I keep my eyes out.

David
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Old 11th Nov 2018, 4:47 pm   #6
Ed_Dinning
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Default Re: Amateur radio HF linear amp

Hi David, I can possibly supply mains transformers, chokes and period HV caps if you need any.

Ed
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Old 11th Nov 2018, 5:23 pm   #7
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Default Re: Amateur radio HF linear amp

Most commercially made amateur radio linear amplifiers are aimed at being used after 100W transceivers and put out a fairly comfortable 400W for the British market and up to 1.5kW for the American market.

So to start with 15W means you're looking at either 2 stages, or a rather high gain job. Most of the techniques for making good, linear amplifiers with solid stability and no neutralisation twiddles limit the gain to less than you're seeking.

The 813 is a good valve for gain, if used as a tetrode without anything fancy. So passive grid is out, as is G2FAF's trick of rectifying the drive to bias the screens. But 813s set up for high gain need careful parasitic stopping.

Anyway, you're outside the range where the usual amateur radio manufacturers tread.

Buying a homebrew linear is probably best if it's to a recognised design and well made, but this also falls into the 100W drive expectation.

If you buy anything homebrew it may be best to view it as a collection of parts and to look for a published design which covers what you want.

Me? I've got a pair of MRFE6V2300 devices sitting in the drawer, samples from a previous investigation. Oodles of power and >20dB gain, so some room for feedback. With semiconductors, the risk is you may kill several in developing a high power amp. With valves, the risk is that they'll kill you. Take care either way.

Come to think of it, there was a Racal linear amp to go after one of their exciters... that used a distributed amplifier architecture. That ought to do what you want. Plenty of gain, easy stability, broad band, valves and pretty tough. Valved. Can't remember the model.

David
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Old 11th Nov 2018, 5:38 pm   #8
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Default Re: Amateur radio HF linear amp

Thanks David


Yes I appreciate that my gain is rather high. I cant really see it working, and never have although Elecraft kxpa500 i think runs off the 15 kx3. I THINK. But this is thousands.

Ill have a mooch and keep it simmering away.

D
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Old 11th Nov 2018, 5:39 pm   #9
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Default Re: Amateur tadio HF linear amp

Quote:
Originally Posted by MrBungle View Post
I built one of these and it works really well: http://hfsignals.blogspot.com/p/25-w...40-and-20.html

Interesting. I built the walford 45 watter a while ago which worked well. Ideally id like a bit.more

D
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Old 11th Nov 2018, 7:38 pm   #10
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Default Re: Amateur radio HF linear amp

Perhaps a Racal TA 1816 - 500W Solid state for 10mw drive.

They arent exactly desktop though
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