Re: LF: Linear Amp for LF

[gw8glo@aol.co.uk]

Andy I have used an ENI amp, the 1140L. These work well at 136 with up to 1.5kw on my amp. They are very inefficient as would be expected. They are also very expensive unless you are lucky, mine came from a 50kw tx and was the grid drive amp! I have benn able to transmit Opera WSPR and PSK31 at the same time using this amp with no problems. Mine needs a 110v supply and is not isolated so I use a 5 kw transformer to do the job.
73 Dave

-----Original Message-----
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>; rsgb_lf_group <rsgb_lf_group@yahoogroups.co.uk>
Sent: Fri, 8 Jan 2016 21:48
Subject: LF: Linear Amp for LF

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