Thought on OTL tube amps

I read the patent many years ago. I suspect Al has too.

The transformer is impedance matching. It is air core, as it is operating at RF frequencies to modulate the output of a switching power supply. The output of the switching supply then has its RF component filtered out and the result is the audio signal. So the output transformer and the switching supply work in tandem to do the impedance conversion.

A conventional output transformer does impedance matching as well only it does it at audio frequencies.

Either way there is a transformer that represents the load to the output tube or tubes. It can only be called an OTL when a transformer can no longer be called a transformer. Since these terms have been with us a long time and will continue to be with us for decades to come, the result is that the acronym 'OTL' is misapplied to this amp.

Ralph is from Minnesota(I might be wrong) and in Minnesota you need lots of heat in the winter. OTL amps partially solve the heat problems.

Maybe the acronym OTL should be changed as applied to David Berning's ZOTL amplifiers as the original ILOT design, iron less output transformer.It never ceases to amaze how this topic is continually debated after all these years. Al you REALLY need to check the archives, if you haven't already, I'm sure you'll find it quite interesting particularly the thread where Ralph and David have a lively discussion of this topic, I think you'll enjoy!

I'm not too sure David EVER called it an OTL, I believe it was Harry "Gizmo" Rosenberg that first did but I may be mistaken. One thing for sure after it was forevermore designated OTL by some, it was equally or more declared NOT by others.

10-30-15: Czarivey
....in Minnesota you need lots of heat in the winter. OTL amps partially solve the heat problems.

True story ....

Our living room is on the main floor & houses the furnace thermostat; the room is hardly used any more as the family room is where the guests go at the other end of the house. Hiding from my wife in this living room - a pair of modded Acoustat Model 3's. So one very cold Ontario winter day, I decided to put my OTL's in there, fire them up with the model 3's and do some listening at - low - moderate levels. It was going great. 2 maybe 3 hours had gone by ?? Not sure.. Then my wife opens the door on me and her first words were ...

"why is the house so cold",

quickly followed by ....

"Hey why is so hot in here",

followed by.....

" Hey..Why the hell are you in your underwear !"
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Ralph, yes I had looked at the patent, and I completely agree with your comments.

Tubegroover, thanks for the suggestion! I'll be sure to check out those discussions. Prior to this thread I had no awareness of this amp, as I mentioned earlier, so I'm sure I will find it to be of particular interest.

Best regards,
-- Al