Running two transformers in parallel?

[SlowPaw]

Hi, all. I'm in the middle of building a 100W tube amp not horribly different than a Fender Showman, when all of a sudden one of those thoughts occurred to me...

What if I doubled the output stage to create a real screamer?

Past history suggests I should drown such thoughts in more beer and stick to the original plan, but it got me wondering about the transformer part of doing such a thing...

Can I "just" run two output trannies in parallel?

[Old Tele man]

...uh, "Yes," it can be done, but WHY?

...if you really want to use TWO separate Output Transformers, why not just split the 4 x 6L6 tube into a pair of 2 x 6L6 output like this: 2 x (2 x 6L6)?

...that way you could run 6L6's on one OT and EL34's on the other OT, etc. (assuming proper speaker and winding taps used).

[SlowPaw]

Sorry if I wasn't clear on my motivations... My goal is to roughly double the output power, and I'm assuming (haven't checked the specs) that the Showman OT will not pass 200 watts.

Surely Fender had these custom made, given the volume they consumed, so it seems likely that running 6 or 8 6L6s into a single OT will fry it.

I'm thinking that I'll have very little luck finding a suitable OT that will handle twice the current, but maybe I could run two in parallel...

Did that make more sense?

[SlowPaw]

And now that I re-read your post, I think I see what you're saying. I could drive two separate speaker cabs, from parallel (4) 6L6 output stages, rather than tying the OTs together on the secondary side.

I was hoping to have a single output (to a 200W mono cab), but that wouldn't be absolutely required.

[Steve Conner]

Marshall's original 100W plexis worked exactly that way. Jim Marshall used two 50 watt universal O.Ts in parallel.

If you're really power-hungry, NOS O.T.s from the Fender 300PS show up on Ebay every so often. One of these 16lb monsters would eat 8 or even 12 6L6s for breakfast. I bought one, but now I wish I'd gone for two smaller transformers so I could use the thing as a stereo amp too.

[SlowPaw]

And, what does it all mean?

Thanks, Steve - good info.

Any observations on the implications on either side of the OTs? I'll look up an old Plexi schematic to see what Marshall did, but I'm wondering...

Two OTs in parallel, hooked to the same (4 or 8 ohm) load I'd normally hook one OT to... does it do anything to the impedance seen by the output tubes?

[Steve Conner]

No. If you hook, say, two 4000 ohm to 8 ohm OTs in parallel, they'll still transform an 8 ohm load to 4000 ohms. The only difference is that the leakage and magnetizing inductances, and winding resistances, will be halved.