Any benefit for 2 Parallel 50 watt OTs?

[frost]

Hey there,

I'm curious if there are any benefits or consequences for using two 50 watt OTs for a 100 watt amp (1 OT for each pair of tubes). Obviously, this would cost more, probably be heavier and take up more chassis real estate. However, is there an adavantage for doing so? I have seen a few high end boutique amps that are doing so and have been pondering this for some time.

Thanks,

Heiko

[Tom Phillips]

I see no advantage if all you really want is a 100W mono musical instrument amp. You already listed some of the disadvantages. Another is possible problems that will happen due to imballances between the two 50W sections when you try to hook the outputs together. Or did you intend to drive different speakers with each OT?

[Enzo]

Keep on mind that boutique amps have to have something to make them special. Marketing is important. Dual OTs? How novel! Gonna drive separate speakers with them? They might claim that separate OTs allows the pairs of tubes to be balanced individually or something. Of course that implies differences, and those differences would then be trying to join to gether when those secondaries are parallelled into the speaker. Then again, isn't it simple to get a matched quad of tubes than to make two pair fit together. For that matter bias twiddles for each socket gets there too, and a lot cheaper.

[Ray Ivers]

Heiko,

It's kind of late here and perhaps I'm not thinking clearly, but if you had two single-ended stages - each with its own SE-type OT, and driven in opposite polarity - and connected the OT secondaries in series, pseudo-push-pull operation with no cancellation of even-order harmonics should result.

Just a thought.

Ray

[frost]

Hey guys,

Thanks for your repilies; I appreciate it. It has just been a thought of mine that has been on the backburner for a while. It looks like I'll stick to just one 100 watt OT.

Take care,

Heiko

[andrew4566]

One advantage I can see is that you could set them up with two tubes on each OT it would be possible to switch one set off for a 50watt setting without as significant a change in tone.

-Andy

[R.G.]

There is one advantage if you do it right - reliability.

If and only if you actually make this into a two-power-amp setup by going ahead and using two more tubes to make two full power amps, a failure in one amp will not kill the other amp and you could go on playing. It makes sense to also do two power supply transformers and chokes though if you're going to do this. That way, all the high-failure-rate stuff is working with a hot backup and any single failure will not put you off-line.

I would not recommend paralleling two OTs into four output tubes. At least drive one OT with a pair of tubes and parallel the tube drive. What to do with feedback and what happens if the drives, tubes, and OTs are not really identical starts getting sticky very quickly in haphazard setups with parallel paths. Better to make a clean separation at the power amp level - unless you gotta have a gimmick.