[AMRadio] Pw Supply

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Wed Dec 6 09:03:23 EST 2006

I would not buy anything from MFJ!

Why the big hurry, wait to find a good transformer,
they are around.
What ratings are you looking for?

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.

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.
For small supplies with steady loads, that is ok,
but for big supplies with loads that vary its not
good. On key up, a cap looks like a dead short till
it charges up, a choke looks like a resistance
in series with the voltage...a big difference...

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.

The old Bill Orr handbooks have loads of great info about power
supplies in them.


> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jack Schmidling
> Sent: Tuesday, December 05, 2006 11:12 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: [AMRadio] Pw Supply
> I am not having much luck finding a HV xformer for my power 
> supply so an 
> idea occurred to me that I would like to pass around.
> MFJ has a 900v one for about $100.  Is there any reason why I can not 
> use two of these and tie one side of the secondaries together 
> and call 
> that the center tap and have an 1800v ct transformer/s?
> I am using 866's so I must have a center tap.
> Second question is:
> Mine has the HV going to the choke and then to two 4 mf 3kv caps in 
> parallel.  Is it not more conventional to put a cap on each 
> side of the 
> choke or two chokes for a choke input filter?
> What would I gain or lose by moving one of the caps to the HV side?
> Thanks,
> js
> -- 
> PHOTO OF THE WEEK: http://schmidling.com/pow.htm
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