[AMRadio] Pw Supply

Jim Candela jcandela at prodigy.net
Wed Dec 6 13:06:19 EST 2006

> 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?

Reply from Jim, JKO:

   No you cannot do this. For full wave center-tap rectification the two windings must be on the same core. If you try this, it may appear to work, but the combined primary currents will be high by 2X from a single transformer. Those MFJ transformers are intended to work into a full wave voltage doubler circuit where 900 x 1.414 x 2 = 2545 volts unloaded, and about 2 kv loaded. This can work, but the capacitors need to be big, and a soft start circuit is needed. Not a good choice for "Push To Talk" B+.

   Take those two transformers, and with a full wave bridge on each one, series up the DC outputs. You will get the same unloaded voltage, but with MUCH better regulation. You could also run choke input filtering as well, but the output will drop to about 1600 volts.

   You are better off with better iron and just one transformer.


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