[AMRadio] Pw Supply

Jack Schmidling jack at schmidling.com
Wed Dec 6 10:04:53 EST 2006

Brett gazdzinski wrote:
> I would not buy anything from MFJ!

The transformers are Ameritron for whatever that is worth.

> Why the big hurry, wait to find a good transformer,
> they are around.

I have wanted one of these since 1955.  I have waited long enough 
besides, at my age, time is at a premium.

> What ratings are you looking for?

Good question.  Actually, I was going to post a question so I could 
answer that one.

I can't make any sense out of the 813 specs, either in the Handbook or 
the data sheet I got on line.

As near as I can tell, the "typical" voltage for AM is about 1300 but I 
see the Maul talking about 2000.  I see plate current at about 150 but I 
see elsewhere 250.  I am sort of confused but think that 2000v ct at 1/2 
amp would do the job.

> Is it supposed to fit on the deck over that big hole?


> Fair radio used to sell a nice oil filled Collins
> transformer, 2250 volt ct at 650ma, 110 or 220 primary.
> With a variac that would give 0 to 1500 volts.

I don't see anything like that on their site but I will  check further.

> Its always much better to go with choke input, much better
> voltage regulation, much lower startup surge current.

> With a cap input, the voltage will increase quite a bit,
> but will sag big time under a load.

Good info.  I read somewhere about needing some sort of step start and 
mine has a time delay relay but it doesn't seem to have anything to do 
with charging caps.  It connects to something in the RF deck which I 
haven't run down yet.  It has a high/low switch which applies either 110 
or 220 to the primary of the HV trans.  Would this be adequate step start?

> What are you going to run off the supply?
> 8UF is not very good for a modulator, I always go
> around 40UF for energy storage.

Unfortunately, I want to run the modulator and rf deck from this supply. 
  That would be 813's/811's.

This package I bought was a linear so that could explain the too low cap?


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