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| To: | [email protected], [email protected] |
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| Subject: | Re: [rsgb_lf_group] Re: LF: Wolf Test transmission running |
| From: | Andy Talbot <[email protected]> |
| Date: | Mon, 29 Feb 2016 12:21:00 +0000 |
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Ah... SRI, if I blocked your last bit of listening for TAG/DES.... Think I must be getting old and doolally :-( Testing a linear PA I completely forgot I had, and, more to the point and worryingly, don't even recall much about building. It has been sitting in my loft for many years, with a price label on having been unable to sell at a few rallies. It looks like a G0MRF design, but using 2SK413 devices which are designed for audio amplifiers - not specifically switching types. Four devices, in 2+2 push pull running off 50V it seems to be delivering 250 Watts happily at the moment. I've also added feedback around each pair consisting of 820 ohms 2 Watt in series with 220nF The PA is built into the same casing as my old 73kHz unit that originally used two Maplin amplifiers in bridge and delivered 180W; that wouldn't work very well on 137kHz and I do - now- recall taking the modules out and building this MRF design. But, for some reason never used it in anger. Maybe because that was the time I was developing the 700 Watts switchmode one which was much more exciting It was all so long ago... Anyway, the whole thing is fully metered, with DC current RF voltage and current and heatsink temperature all available on a front panel meter. Switchable taps on the output transformer for 50 - 200 ohms antenna R. Gain rolls off but it does seem to give about 180 Watts at 475kHz, probably due to the driver I used, which is... wait for it.... A . [something]2000 (that's what its labelled, anyway) audio power amplifier in TO220 can. Probably a TC2000 looking at my datasheet archive, there is a file for that device, dated 1998 So hardly surprising gain is down at MF I'm soak testing it at the moment. Those FETs aren't really suitable for 50V working with uncertain loads. They are rated at 160 V max, so with a 50V rail see 100V anyway so a bit close for comfort. But I'm going to soak test it anyway! So, to recap - the signal your are getting from me now is 7.5dB up on yesterday's There is the added advantage, I can use the 50V SMPSU which suffers no heat problems at all, and laughs at the 9 - 10 Amps this PA is drawing Andy G4JNT On 29 February 2016 at 11:58, Steve Elliston [email protected] [rsgb_lf_group] <[email protected]> wrote:
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