B+ PT Current Question

[MarshallPlexi]

Question.

I need to order a PT, and I need to have 310VDC using two EL34's in Class A. The tubes would idle at 83mA each, so I'm assuming that the total B+ current will be 83+83+misc (preamps etc.) = 200mA. I'm going to wind the B+ winding for 230-0-230, which I think should get me in the ballpark

230 * 1.4 = 322VDC roughly.
322 - 5% = 306VDC roughly.

My question is this. If I were to spec the B+ winding at 300mA, would the B+ rise even if I wasn't using this additional current that is available?

This simple problem has confused me for years.

Thanks!

[Moose]

Current DRAW is what matters. Always.

The rating of a tranny is how much you can draw before danger of damaging the transformer. It doesn't force that amperage down the pipe, or anything.

Kind of like a circuit breaker. 15A on a breaker doesn't get delivered all the time. If you plug in a 10A router, you'll only pull 10A. The rating just tells you that if you try to draw 20A, the breaker's going to pop because it's 5A over what can be delivered.

[MarshallPlexi]

So in theory, I could have the B+ winding at 500mA and still not see a voltage rise and it would deliver it's rated voltage UP TO 500mA and then start to sag?

Thanks!

[Moose]

Yes, though I do NOT suggest overworking your tranny to make sag. Sag at the tranny means heat at the tranny which soon means no more tranny. Bad juju.

You want sag, get some resistance in there with an appropriately rated power resistor at the recto.