# Mystery transformer, providing voltage for vacuum tubes.

Discussion in 'General Electronics Chat' started by Thecomedian, Feb 28, 2015.

1. ### Thecomedian Thread Starter New Member

Oct 12, 2013
22
3
I found this old 15 pound transformer, and its got 10 lugs. There's a hand written piece of paper for its schematic saying that it has 4 primary lugs, and was putting out 14V on secondary 1, 20V center tapped on secondary 2, and 8.5V on secondary 3. It also says 15A by the secondaries, and says "using 220V mains" on the top.

This all looks like someone's tests of it, so I was wondering, does the 15A 14V mean that its actually 210V @ 1A if I were to reduce the current? Is there certain "expected" values of secondary outputs which I can hone in on by testing it? I notice that the transformers for supplying tube amps here provided an expected voltage/current value such as 325v and 200mA, for example. https://www.tubesandmore.com/products/P-TF22798

Would I see a larger climb in voltage with more resistance on the secondaries and reduction in current below 1 amp? If you have a transformer that isn't specifically set up to output exactly what you need, is it a waste of electrical power, in dissipation terms, to bring the voltage and current of a larger than necessary transformer into the pocket of desired V/A output?

2. ### crutschow Expert

Mar 14, 2008
13,477
3,362
The output voltage of a transformer will change some from no-load to full-load due to the internal winding resistances, but it's usually no more than about 10% for well designed transformers.
So a 15A @ 14 V winding will certainly not give 210V @ 1A.

You need a transformer that has a secondary voltage near what you need. Otherwise you just waste power.

Thecomedian likes this.
3. ### Thecomedian Thread Starter New Member

Oct 12, 2013
22
3
Thanks man, this is the kind of idea I was hoping to get. I dunno what the thing is actually for, then. 3 low voltage windings and weighs 15 lb... might be for running a microwave or a bunch of power transistor stuff..