Thought on OTL tube amps

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

BTW, David most certainly does call his amp an OTL. As Atmasphere states above, the transformer in the Berning amp operates at RF frequencies, while the output transformer of a conventional amp operates at audio frequencies. That is why Berning refers to his amp as an OTL. Those who say otherwise are obviously invested in saying otherwise.

11-25-15: Psag
... That is why Berning refers to his amp as an OTL. Those who say otherwise are obviously invested in saying otherwise.

Certainly not true in my case, apart perhaps from whatever negligibly small interest I might have in not having my original statement that it is not an OTL contradicted.

Also, Ralph makes a good point that the term "OTL" is normally used just in the context of tube amplifiers, since the vast majority of solid state amps don't have output transformers or autoformers anyway. And since the Berning's output stage utilizes solid state switching devices, it arguably does not even fall within that context.

Regards,
-- Al

Perhaps I should put my $0.02 here from an end-user perspective.

I have owned at least seven (7) different OTL tube amps, some are big brands, some are DIYs from experienced (10+ yrs) tube amp hobbyists with extensive engineering experience.

IMHO, OTL tube amps are reliable if you understand their operation limitation first. I found that:

1) OTL tube amps do not work well under 4 ohm or less speakers. Even some transient passages at 2 or 3 ohms may blown the tubes. This is not specific to the tube type.

2) OTL tube amps are much less tolerant to wide impedance swing. The more stable the speaker's impedance, the better.

The best sound I got from OTL amps is when I use them to drive impedance-friendly monitors, with the aide of quality subwoofers covering 180Hz-250Hz and below.

Hope this helps.