The world's most outrageously inefficient amplifier?

[Cursitor Doom]

[Bill]

In message , Cursitor Doom writes

It is certainly and interesting specification from a supposedly technical company. As it is nearly Christmas and in the spirit of good will I must assume it is a typo'

[Bob Minchin]

300W PEP out for 800W input is about right for a linear wideband amp.

[Cursitor Doom]

Yes, it *would* be I guess - still pretty poor, though. But *this* one appears to require connection directly to a local electricity sub-station.

[Cursitor Doom]

Actually I believe that's 300W CW not PEP. I'm guessing because it's not expressed in the customary technical nomenclature.

[Andy Burns]

Blame The manufacturer, not Maplin, they list 800A

though on their USA site, they've corrected it to 800VA

[Bill]

Indeed 300W out for 800W in is reasonable.

BUT they quote power drain as 800A which is a mixture of units anyway. But if it is 800A at either 110V or 230V then it definitely deserves the title of "The world's most outrageously inefficient amplifier"

I would have hoped they could get their units correct, maybe they will remedy this soon.

[Cursitor Doom]

Thanks for clearing that up, Andy.

[Johnny B Good]

Well, Duh! The "A" should have been "W". 800W maximum, worst case consumption from the mains input is about what you might expect for a

300W output HF *linear* amplifier.

This put me in mind of a 4 valve (PL519) linear similar to this one:

The example I saw at a radioham rally in the late 80s / early 90s (which may have simply been a later evolution by the same guy) was a compact lightweight design where the PSU avoided an expensive HT mains transformer by cleverly fullwave rectifying the mains to produce +/- 350v DC supply voltages applied in series to supply the 700v HT to the PL519 LOPT driver valves.

There may have also been a 40v 50VA heater transformer, I can't recall whether this measure to reduce stress on the heater cathode insulation was used or whether they'd simply been wired in series with a 'dropper' across the mains supply. Paralleling the valve anodes neatly reduced the output impedance feeding the Pi tuning network which reduced the voltage requirements of the input tuning capacitor which all contributed to its rather compact size compared to the more 'conventional' valve designs in common usage at that time.

I was impressed by this 'lateral thinking' approach but not quite enough to buy or build one for myself. However, its 'cleverness' did leave a lasting impression (enough at least, for me to give it 'An Honourable Mention' here). Despite its 48W heater 'vampire load', I rather doubt it drew more than the 800W quoted for its modern counterpart, the RM BLA 350.

[Johnny B Good]

I too thought the use of "Key Down" instead of "PEP" was rather odd. Perhaps they were referring to its ability to sustain very high duty cycles using extreme speech processing that would hold the average power level close to the PEP limit to give it the classic "Radio Bulgaria" punch through the QRM/QRN effect.

[Cursitor Doom]

Nope. It's an informal ham term for an unmodulated carrier wave such as you get in CW mode on a transmitter when holding a morse key down. PEP is the correct measure for this purpose (using two harmonically-unrelated tones as drive) and gives a significantly higher figure.

[Johnny B Good]

I was aware of that which is why I thought it a rather odd way to describe the power rating of a class A/B 'linear' amplifier. If all you need to is to boost the power of a simple CW 'exciter', a more efficient class C amplifier (with a highish Q tuned Pi load matching network on its output) would be a more elegant solution to going QRO.

[Bill]

This might be classified as QRO?