Paralleled heater windings for more amperage?

[Squidward]

I have a power transformer with a HV winding, and four other windings at 6.3V. THey are 3.0A, 0.9A, 0.6A, and 0.3A. I want to run a circuit that needs 4A @ 6.3V. Is anything stopping me from using the 3.0, 0.9, and one other winding in parallel to make this work? I can still use the remaining 0.6 or 0.3 winding for other purposes (like heat for a preamp tube), too, right?

Thanks!

 

[bricktop]

If I knew the geometry of the windings, I might be inclined to....but (always a but) - those multiple secondaries may not be all the same number of turns, have the same coupling, etc - so you may end up with a type of short and excess current between each, even if they were wired in phase. You may, however, be able to just take 4A from that 3A winding, and leave the others unused. Just need to find the winding dissipation and make sure it doesn't get too hot (hard to say what too hot is - probably more than a few watts per winding, depending on the core size).

I'd only parallel windings if I knew that they were bifilar/trifilar/etc.

 

[GordonW]

What's the load? Is it a set of four output tube heaters?

If so, there's no reason why you couldn't hook three of them onto the 3 amp winding, and the other on the .9 amp winding, like so:

Even if the heaters are "referenced" to other voltage sources (other than ground), there's no reason why the common node couldn't just be hooked right there, for hum balance... they'd all be at the same DC potential, and see the same "signal" from whatever they're hooked to...

Regards,
Gordon.

 

[Squidward]

The application is indeed to heat tubes, but each tube could draw 2A each. I've since decided to go with a different tube for the circuit, sounds like it will cause me less headache in the end.

Thanks for the info, Micah!