When were the best tube amps made?

Transformers are the key element for both SET and push pull.  Even for OTL the power transformer is relevant.  Likely the best commercial winders were in Japan in the late '90s, companies like HIrata Tango and Tamura.

@rogerh113 Excellent power transformers can be made by a good number of companies here in the US.

If you take an OTL and run the ZERO autoformer on it, you wind up (if you see what I did there) with the possibility of an amplifier with much greater bandwidth than any conventional tube amp. This is because the ZERO has such low turns ratio and extremely low distributed capacitance that its bandwidth is very wide- about 2Hz to 1 MHz- wider than any tube amp made. Usually the bandwidth limitation is in the output transformer.

@atmasphere,

not sure whether Zero Autoformers are really zero cost. I used them on a Graaf GM20 about 15 years ago and while bass was significantly tightened, the overall SQ lost pizzazz. It felt a bit like a Ferrari on Qualudes…

In a talk Roger Modjeski (Music Reference, RAM Tube Works) said Tim de Paravicini (EAR-Yoshino) told him he could tell what a tube amp sounded like by looking at it’s transformers. Both Roger and Tim extensively studied the art and science of transformer design, and wound their own.

not sure whether Zero Autoformers are really zero cost. I used them on a Graaf GM20 about 15 years ago and while bass was significantly tightened, the overall SQ lost pizzazz. It felt a bit like a Ferrari on Qualudes…

@antigrunge2 The result depends largely on the interface of the amp to the load. In our case, it works really well if the load is lower than the amp is comfortable with. There are tradeoffs if part of the load (like the mids and high) are easy to drive while the woofer isn't. However sometimes in that case, if the speaker can be bi-wired, you can run the ZERO just on the woofer to correct the impedance and run direct on the mids and highs.

If the amp uses feedback, as in the case of the Graaf (IIRC) then its a good idea to have the feedback at the output of the transformer, which would take some work... So its not a cure-all solution, but it is one that can be very effective if the stars align.

today - Japan

Luxman SQ88uC sounds awesome!