I agree about MOTs. It didn't take me long to decide that, for a big
amplifier, they're just not worth the bother. My home-rewound plate xfmr has
multiple taps on both primary windings and the secondary winding:
Vin = 100/120/200/240
Vout = 1180/1266/1353/1440 @ 3A
My target out of the FWD is 3500 to 4000V @ > 1A (max load = 785 mA). The xfmr
came from a piece of medical equipment, with a split bobbin (low leakage
current). Total investment (wire + NMN paper) ≈ $150. Thanks to Manfred and
others!
vy 73,
Bryan WA7PRC
> From: Jim Thomson
> Subject: [Amps] Microwave Oven Power Transformer
>
> From: Bill Turner
> Subject: Re: [Amps] Microwave Oven Power Transformer
>
> Guys.... it pains me to see you screw around with a
> transformer which was
> designed to cook food.
>
> Save your pennies, get a real Peter Dahl transformer and be
> done with it. Build
> it into a universal power supply you can use with any of
> your amps and it will
> last you the rest of your life and your children's and
> grandchildren's too.
>
> That will be two cents, please. :-)
>
> 73, Bill W6WRT
>
>
> ## MOT?s are a pita. They all have sky high primary
> magnetizing current. And that is caused
> by not enough primary turns ! The primary to
> sec turns ratio remains the same..as a real xfmr.
> You really need between 2 or 4 of em ( all identical)
> to do the job right. You also have to
> knock
> the shunt out of them with a drift
> punch. One side of the sec on most of them
> is bonded to the frame,
> IE: grnded. Even with 2/4 of em, you still
> have sky high magnetizing current.
>
> ## using a series drop resistor in one leg on
> RX... + a relay to shunt out the same resistor on TX
> will work, but
> its still a pita.
>
> ## Time to get off the ....?get cheap program?
> and just do it right the 1st time. Buy a
> new dahl 46-68-86-120 lb
> xfmr with LOTS of primary AND sec taps. Get the
> primary tapped for 220/230/240. Get the sec
> tapped at several voltages.
> Like at least 4-6 sec taps. Then you now
> have a xfmr that will run any amp you can think of.
> Its resale value will be
> a LOT higher....with all the taps. Your wife and kids
> will get all their $$$ back out of a good xfmr...which means
> one that
> can be used.
>
> ## The heart of any amp project is the HV
> supply. And the heart of the HV
> supply is the plate xfmr. Screw that up, or try and
> go cheap, and lose it right there. The big
> xfmr?s are the way to go. They don?t break a sweat,
> don?t heat up, and best of all, their
> V regulation is a helluva lot better. On a
> buddy?s hb 2 x GS35B 6M amp, he had 2 x xfmrs to
> play with. One of em resulted in a
> 700 vdc v drop. The bigger one resulted in
> a 50 vdc V drop...and loads more po. You
> don?t put a light duty eng in a dump truck.
>
> later........ Jim VE7RF
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