There a few "audio" transistors about, I am using Toshiba complementary
pairs 2SA1947 and 2SC5200 (4 of each) with 320W dc input. Naturally
there is plenty of heat to dissipate so I fitted large heatsinks and
cooling fans, using no insulating pads, the heatsinks are "live". The
power supply is linear and.shortly to be upgraded to provide at least
500W dc input.
No transmissions at the moment, I have an analogue IQ generator board to
fit as my IQ software has failed.
Hugh, M0DSZ
On 08/01/2016 21:45, Andy Talbot wrote:
Are there any proven reliably designed LF amplifier designs power
amplifiers for 137 / 475? Wideband, covering both ideally Rated
for at least 300 Watts output, and ideally a lot more.
I saw G3YXM's low-HF design, and it looks promising for low frequency
use, but he appears to have not gone that way and went for a
switchmode version at LF/MF
Of course, I could just redesign that, or something similar, using
suitable ferrite and a bit of feedback ,but it would be nice to avoid
reinventing too many wheels.
Using switching MOSFETs as linear amps still doesn't feel quite right,
but enough people seem have managed it now (including my own design
for a low power one) that it looks a sound-enough route to follow up.
The one thing that does bother me about the technique is bias
compensation with temperature. It is really asking for active bias
control, but in a class-B or -AB design, where bias just affects
standing current, that gets more-than a bit tricky as a concept.
Andy G4JNT
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