[AMPS] Alpha (HOME BREW OR NOT?)

[Barry Kirkwood]

The issue of light weight amps has come up before.
Deserves serious thought.
PL509 tubes could have filaments seriesed to run direct from mains, saving a
filament transformer.
Keep thinking back to those old DC-DC power supplies we used to use. Couple
of power transistors running from 12V dc with a ferrite toroid transformer
running at audio freq sinewave, rectified and needing only small C for
filtering, altho issue of reservoir capacitor would arise with linear amp.
There were plenty made to give 800V for transceivers of the day.
Wonder about rectifying 230V ac to feed a power oscillator at x kHz and
feeding a lightweight transformer to give several kV.
Or am I being silly?

end
Barry Kirkwood PhD ZL1DD
Signal Hill
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
www.waiheke.co.nz/signal.htm
----- Original Message -----
From: Hans Goldschmidt <sm5ki@algonet.se>
To: Michael Tope <W4EF@dellroy.com>; Bob Marston <k1ta@contesting.com>;
<w7ti@jps.net>
Cc: <amps@contesting.com>
Sent: Sunday, 31 December, 2000 1:16 AM
Subject: Re: [AMPS] Alpha (HOME BREW OR NOT?)


>
>
> It is much cheaper to buy a used SB220 for little money then trying to
> collect parts for a homebrewed amp. If you are an old timer with a big
junk
> box or visit a lot of flea markets, you may be able to collect enough
parts
> to be able to build a much better amp with better parts than the
commercials
> could afford. And cheaper too. You may find an overrated transformer or a
> vacuumcap that would be too expensive for a relatively lowpriced
commercial
> amp.
>
> The charm with a homebrewed amp is that you can build an amp to meet some
> special preferences. Lets look at my problem:
>
> I travel a lot in summertime and like to operate portable from DX spots
like
> OH0. I have a bad back and no drivers license. So, the amp must be low
> weight and easy to transport. Then there are two choices:
>
> Build a low profile rf unit and separate power supply to be transported in
> two suitcases.  As it seems there are no high voltage switched power
> supplies avaiable, will then use a low profile hi-voltage swedish toroid
> transformer that still are on our surplus market.
>
> Or, build a number of normal power supplies that could be staying all year
> around in the qth:s I normally use and only carry the rf section with me.
>
> Could use 3 himu triode connected 8072 tubes in paralell with homemade
> external coolers similar to the EIMAC 8875s. Cooled by two flatpack
blowers
> for low weight and size. To further lower the cooling requirements could
use
> instead a supercathode, a DAF ( here we go again,hi!) or a carrier
> controlled bias system to lower anode dissipation. The box could be made
of
> glass fibre laminate still giving rf shielding and low weight.
>
> I need only need a few bands. But, for all band coverage I can use small
> sized variable capacitors plus the the high voltage high current LCCs and
> toroids I already have. That could be switched in with the hi power relays
I
> already have also.
>
> The 8072s are quite cheap in Scandinavia - I have a number of them. The
> control grid can take 100mA and one can assume the screen grid can take
even
> more. I have anumber of them but only one socket, so far. Anyone?
>
> This system cannot be found on the commercial market and I must build it
> myself. Transistorized amps still are no low weight and not considered.
>
> What say - any comments or suggestions?
>
> Happy New Year to all from Hans SM5KI
>
>
> --
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>
>


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