On Mar 9, 10:02�pm, raypsi wrote:
On Mar 8, 9:23 pm, JIMMIE wrote:





On Mar 8, 7:32 pm, wrote:

On Mar 4, 7:20 pm, JIMMIE wrote:

Ive been playing around with some old UPSs that are the switch mode
type, the ones without the big iron transformers. I m not sure if I
have a handle on how they work or not but it seems very similar to a
Class D amplifier amplifiying a 60HZ input, well sort of. It seems
like they dont actually input a 60Hz signal rather they just go
directly from digital by generating the pulse width modulated
waveforms with a computer. I was thinking that a transformer might be
placed before the output low pass filter to step up the voltage for
tube circuits, maybe even a TX PA. No doubt for this to have any merit
the LPF would have to be redsigned.

Jimmie

There are a number of different topologies. �One is to convert the
120VAC to 167VDC and then chop it up, usually 20khz and feed that to
transformers to convert to the desired voltages, and then rectify and
filter it once again to get the DC outputs.

The utility of a SMPS is the efficiency, and the light wieght.
Efficient because it operates class D and light because the magnetics
at high frequencies are much lighter than 60hz.

The downside of SMPS is the electronics are rather complex, and the
magnetics are hard to (for me) design.

I don't see any reason you could not modify a SMPS to get a couple KV
for Tube operation. �Seems I remember someone advertising a SMPS
capabible of KV output, but I can't put my hands on it. �Keep in mind
that a SMPS will tear up you receiver all up and down the bands unless
it is very well designed to eliminate noise.

I use a commercial 50VDC 22AMP SMPS to run my 600 watt solid state
amp.

73 Gary N4AST

Gary I have likewise used a UPS for a DC power supply by taking the
voltage of from across the batteries. I briefly had a similar amp that
I was repairing for a friend and thats the way I powered it.

Jimmie

Hey OM

Sometimes you see 2 �transformers in these SMPS and one is a magnetic
amplifier. Just before transistors took hold they were using mag
amps . The Germans were experts in mag amps and we got the tech from
them after WWII. I think one could have a mag amp for each hf band.
Who knows if it weren't for transistors we might be using mag amps all
over the place. You can't get much simpler than a hunk of wire on a
magnetic core, there's no money to be made there. And mag amps don't
blow out like semiconductors. they aren't effected by huge EM pulses
either.

73 OM
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Mag Amps were used quite a bit in battery chargers, AC motor controls,
AC generator excitation systems, voltage regulators ect., they were as
you say, simple and rugged. I think it was in the 80's when power
semiconductors started getting bigger and better that they started to
get phased out. There is a book about mag amps written in 1960 that
you can download on the free tech books site. It talks about how
amazed the British engineers were at the Germans use of mag amps in
their rockets and fire control systems. Even though vacuum tubes had
been around for several years, the Germans discovered that mag amps
were superior in many applications.

I don't think they would make a very practical HF amplifier, because
they operate with AC supply voltages. They will not effectively
amplify an AC voltage whose frequency is any higher than its supply
voltage frequency. That is why mag amps usually operate at 60HZ,
there are plenty of 60HZ power supplies around.

Gary N4AST