Dual Primary OT - Is this possible?

[MarshallPlexi]

It is possible to use one OT with dual primaries for two completely separate sets of tubes and have them share a common secondary? I included a sketch to show what I'm talking about.

I've seen Marshall use dual OT's but I've never seen this before.

[Stevem]

Sure, as long as the plate voltage is cut off from the unused output tubes.
Hammond kinda does the same thing on there OTs ( non stock replacement types), but on the secondary windings.
I am not sure but the duel primary set may not allow for interleaved windings to be done if that's a concern?

[VacuumVoodoo]

SE or PP? your sketch shows SE primary windings.
Keeping a common secondary winding and winding 2 primaries, one having roughly 1.75 times the number of winding turns than the other is not the best idea IMO. The winding with fewer number of turns will have 3x lower inductance resulting in 3x higher low frequency bandwidth limit. Your low end will go out the window.
Two secondaries are better if you must have the option.

[Structo]

Heyboer can wind a dual primary OT.

The OT I got with my D'lite amp had a 4K and a 8K primary so you could run 6L6 or 6V6.

The secondary has 4, 8, 16 ohm taps.

I think it is a 50w OT.

[Blackburn]

I've gotten a triple primary from MM for a JTM build. It has 3.4k, 6.6k and 8k. A big mess but very nice for being able to noodle with different tubes and settings.

[MarshallPlexi]

SE or PP? your sketch shows SE primary windings.
Keeping a common secondary winding and winding 2 primaries, one having roughly 1.75 times the number of winding turns than the other is not the best idea IMO. The winding with fewer number of turns will have 3x lower inductance resulting in 3x higher low frequency bandwidth limit. Your low end will go out the window.
Two secondaries are better if you must have the option.

My bad! They are both push pull. Sorry it was late when I posted that.

Any problems with running two independent sets of of tubes at the SAME TIME with this kind of setup? Like 2x 6V6's and 4x 6L6's?

[bruce egnater]

If your idea is to parallel the two different tube pairs (quads), you would more likely tap the primary at the desired impedances rather than two individual windings. Look at the Boogie Simulclass circuit. Though not exactly what you are doing, it is a similar concept.

[Structo]

In that case what is the total impedance the speakers see?

Instead of 2.2K or 6.6K does the amp see 9K?

[martin manning]

You would have a primary that looks like a UL, where the "inner" taps would be at 1/(6600/2200)^0.5=57.7%. The turns ratio for the "outer" taps to match an 8 ohm secondary would be (6600/16)^0.5.