[raydog]

I recently had a company build a replacement transformer for my Philco 18. It was specced out to be 120v primary / 760v center tapped per the Philco 18 code 124 schematics. Problem is that I am getting 420v from each leg, which means 840v total. The company says that they build in 10% higher voltage under no load conditions. Is this acceptable? The rectifier tube is a #80 which I thought was good up to 800v.

Don

[Ron Ramirez]

Let's see...760 + 76 (which is 10%) = 836 which is pretty close to 840.

The voltage will drop somewhat under load, so I wouldn't be too concerned...yet. It is what the voltages measure out to be under load that will make the difference.

Who did you contract with to build the transformer? On the few occasions I have had to have custom wound transformers made, I used Heyboer Transformers. Expensive, but worth it. And I specified 130 volt primaries, to more than make up for today's higher line voltages. Never a problem with any of them.

http://www.heyboertransformers.com/

[raydog]

I used Edcor out of New Mexico. They are supposed to ship the transformer back to me on Friday. Maybe I could see if they could raise the primary to 130v? Not sure how critical the power supply should be. Just don't want to be stuck with something that isn't going to work.

[Ron Ramirez]

Hmmm...I did not know Edcor did custom work. I have never purchased one of their transformers, but I have heard good things about them.

If they have already wound the transformer, it would be too late at this point to change the primary to 130V since the primary is usually the second winding from the inside - the high voltage secondary is usually the innermost winding. The filament windings are usually wound last.

This is not always true, but it seems to be the rule rather than the exception.

[codefox1]

The output of any transformer will be close to the expected load. Regulation as in core size, will keep it close, but it should be measured in play.

[Arran]

Hammond is another good vendor who will custom wind transformers, but I don't think they rewind originals. Hammond costs more then Edcor apparently, but they under rate their transformers so if something is specified as having a 125 volt primary it will withstand 130 volts not to mention the current ratings are better then what they spec.
As for increasing the size of the primary it's too late for that, the only way around it if line voltage is a concern, is to add a bucking transformer in series with the primary. The voltage that you are getting from the high voltage side doesn't sound far off considering that there is no load.
Regards
Arran