Thought on OTL tube amps

If the Berning folks might be stretching it a bit to call their amp an OTL, what about companies, like Tenor (I believe), that put out a solid state amp that they described as OTL?  This was absolutely true, but, aside from a few solid state amps like models produced by McIntosh, all solid state amps are OTLs (low output impedance of transistors makes transformers unnecessary).

I remember when Allied used to write up the receivers in their catalog back in the early 70s. They referred to their circuits as ITL/OTL and maybe with good reason at the time. A lot of solid state amps back in those days employed input transformers as phase splitters to the output section!

These days though OTL generally refers to a tube amp, not a solid state amp as its no big shakes with solid state in that regard.

Using the Zero in OTL, kill dynamics and will not be OTL anymore.Going back to  PP.

The ZERO will not kill dynamics. The ZERO is a problem solver, used when someone wants to drive a speaker that is lower impedance, perhaps too low for the OTL to do on its own. All you have to do if you don't want to use the ZEROs is get a speaker of higher impedance (8 ohms minimum usually works with our stuff) or get a bigger OTL.

The ZEROs usually get used with our smaller OTLs, an example being our M-60s used with Magnaplanar 3.7s or the like. The result of using the ZEROs is that the output power of the amp is doubled (from 40 watts to 80 watts), the distortion is reduced and the tubes run cooler as the power they are making is dissipated in the load rather than in the output section. MA-1 amplifiers drive the Magnaplanars just fine without the ZEROs.

The ZERO would not be possible if the amp did not already have a lower output impedance and did not make any DC voltage at its output. The result is that the ZERO then has actually greater bandwidth than the amps- going from 2Hz to 2MHz. So it does not limit bandwidth of the amp. The resulting combination is impressive- a tube power amp with full power from 2Hz to about 100KHz or so, which can drive 2 ohms or more. You can't do that with a regular tube amp!

The output can not be equal to input always,How do you categorize amplifier with an output transformer?OTL?Are we going in circle?or we might just go back to SE or PP.The mean reason why  these amp were design is that they will work without OPT.

Al,That's their selling point plus the exotic wooden case, which has nothing to do with sound or else  zero will not be in bizznes,I already ask him,the autotransformer maker  about if it kills dymanics and  he said decide it yourself.Auto transformer works two ways either step up which makes the sound louder or step down which make the sound lower.