[AMRadio] WTB: HV Transformer


Jim Candela jcandela at prodigy.net
Tue Dec 19 12:33:11 EST 2006



----- Original Message ----
From: Jack Schmidling <jack at schmidling.com>

Did some more "research" on that issue and it's a cute idea but as we 
discussed, the xformer has a WV of 1500 (whatever that means) and it 
would be limited to half the current, i.e. 250 ma.


Reply from Jim, WD5JKO,

Jack, I am not sure what exactly those 'WV' ratings actually mean, or how they are rated with a given safety factor. Maybe someone else can chime in with that. In general, some transformers don't like the center tap to float since insulation in that area might be marginal. If all the HV terminals including the C.T. are insulated with ceramic feed throughs, then using a FW bridge will probably work. You raise an interesting point about de-rating a transformer to 1/2 current when using a bridge. Keep in mind the duty cycle of amateur transmitters on AM. This might be 3 minutes on, and 15 minutes off when in a round table. That means the duty cycle is < 20%. As long as the core does not saturate, run it at rated current at 4 times the output power (twice voltage at same current = 4x power, P=E^2/R) so long as the duty cycle is low. Many transformers rated for CCS at high altitude are excellent candidates for this approach.

I am building a power supply for a 8877 linear amplifier, and I plan on using a Collins transformer that goes from 120/240 to 2250 CT at .565 amps (CCS at 10,000 feet). I will be using a FW bridge, and plan on loading the 8877 to 1 ampere at tune up for brief periods. That transformer is BIG and HEAVY, and the HV winding resistance is really low. I don't think there will be a problem, but I'll let you know once I get it built.

My 2 cents,
Jim










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