Manfred,
If this project is the same quality and benefit to the home-builder as
your Fodtrack (and I am sure it will be), please go ahead!
Angel HB9SLV
Manfred Mornhinweg a écrit :
> I really hope it's not too improper to take this thread for my first
> post to this group:
>
>
>> I am becoming more and more disgusted with the lack of technical
>> knowledge QST authors.
>>
>
> If you mean the very usual bugs in the schematics, and omission of
> important information, that's mostly a problem of the editors, not the
> authors. Some years ago I submitted a technical article of some weight
> to QST. It took some work convincing them to actually publish it in QST,
> as it was deemed too technical. Then, they insisted on re-drawing my
> schematics, despite my having submitted them ready to be published. They
> introduced many severe errors. I proofread the article, corrected the
> errors, they made the corrections but introduced some new errors and
> then published the article without further proofreading. Anyway it won
> the cover plaque award, which shows that the readers after all DO like
> to read "heavy" technical articles!
>
> QEX is less "editoriated", so there is a greater chance to get an
> article in without unwelcome modifications.
>
> Now to old amps:
>
> > A fine example is the article about reviving old
>
>> linear amplifiers in the most recent QST. There is a schematic and
>> description of a half-wave voltage doubler which is claimed to have been
>> used on many older amplifiers. But, everyone that I have seen uses
>> full-wave voltage doublers.
>>
>
> You mean full-wave rectifiers?
>
> I own and regularly use, and have repaired, a National Radio NCL-2000
> amplifier. I think it's from 1963 or so. This amplifier indeed uses a
> voltage doubler to make the 2.6kV. In a homemade beast using four 813's
> I also employed a voltage doubler, just to save me a lot of turns when
> winding the transformer! So that makes two.
>
> > Where is Wayne Green when we really need him?????
>
> He's alive and well. I had e-mail contact with him a month or two ago.
> But in my opinion he turned too far away from radio. The last issues of
> 73 I got were more about esoteric holistic cancer-curing stuff than
> about radio, so I discontinued my subscription. Shortly later the
> magazine bit the grass. It's a pity.
>
> Now to the main purpose of my post:
>
> QEX carried two articles lately that are interesting. One is about a
> class AB/F amplifier using TV sweep tubes. The performance of the AB/F
> principle seems good enough for all kinds of ham use, and the high
> efficiency is very attractivo to save space, weight, but above all heat
> and thus fan noise. Then came another article about a 1.5kW solid state
> amp using a pair of ARF1500 MOSFETs. I had been watching these FETs for
> well over a year, but didn't dare to try them due to worries about
> hotspotting, and cooling issues. The rated 1500 Watts are fantasy
> values, unachievable in practice, with 500 Watts being reasonable and
> 700 Watts possible but hard to do. I was thinking about running a pair
> of ARF1505 at 300V, obtained by directly rectifying and filtering my
> 220V AC line, and making the insulation in the RF transformers. That
> would be the ultimate in cheap, simple, lightweight solid state
> amplifiers! But the hotspotting problems seem to make reliable operation
> unlikely.
>
> Then it came to my mind that joining the two articles seems almost
> ideal: A class AB/F amp with ARF1500 MOSFETs would be free of
> hotspotting, because in the AB class it would run at very low voltage
> (20 or 30V at most) and above that it would be running class F. At the
> same time, the reduced dissipation goes a long way in helping with the
> cooling problem. The added complexity of the modulated switching power
> supply would be rewarded by the high efficiency. And the whole thing
> would still be small, lightweight and reasonably cheap. Any takers, out
> there?
>
> If nobody else tries and publishes this soon, I might be the first
> volunteer to try it. What scares me is the risk of blowing up a few
> pairs of FETs during development, at $450 per pair (plus shipping to my
> end of the world, plus taxes). Also, time is scarce, but I guess I would
> steal some time off other activities for this project! I already made a
> crude design, some simulations, and the biggest problem is input
> impedance matching. After all, in class F we need really stiff driving.
> So far it seems that a band-switched LCR input circuit is needed, with a
> separate (but simple) matching network per band, before going into the
> broadband input transformer.
>
> I would be really interested in knowing what you think of this. Am I a
> crazy dreamer (from reading too much 73) and just loosing my time, or do
> you see merits to this approach? Or do I come late, and someone has
> already done it?
>
> Manfred, XQ2FOD.
>
> --------------------------
> Visit my hobby homepage!
> http://ludens.cl
> --------------------------
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