Thank you, Charles. While the Siegfried and certain other Berning amps are described by Mr. Berning as OTLs, and are considered by many to be such, and by all accounts I have seen those are brilliant designs and excellent performers, in between their output tube(s) and the output of the amp they employ a transformer operating at RF frequencies, and also a number of solid state switching devices. Therefore, despite their description and despite the fact that they are considered to be OTLs by many, they are not truly OTLs for at least two reasons:
1)While the output transformer is not an AF (audio frequency) transformer, as it is in most tube amps, an RF (radio frequency) transformer is still a transformer. So the design is not Output TransformerLess.
2)The use of solid state switching devices in the output circuit, which are "after" the output tube(s) in the signal path, arguably makes the use of the term OTL meaningless, since aside from a few McIntosh designs nearly all amps having solid state output stages do not have output transformers either.
I know from past discussions that Ralph/Atmasphere would strongly agree with what I have said.
The patent on Mr. Berning's "Output Transformerless Amplifier Impedance Matching Apparatus" can be found here (although it addresses a push-pull version rather than the SET version). In the first figure note all of the "stuff" between the output tube and the "load" (i.e., the speaker), including a transformer and numerous solid state devices. And note in the introductory text:
Best regards,
-- Al
1)While the output transformer is not an AF (audio frequency) transformer, as it is in most tube amps, an RF (radio frequency) transformer is still a transformer. So the design is not Output TransformerLess.
2)The use of solid state switching devices in the output circuit, which are "after" the output tube(s) in the signal path, arguably makes the use of the term OTL meaningless, since aside from a few McIntosh designs nearly all amps having solid state output stages do not have output transformers either.
I know from past discussions that Ralph/Atmasphere would strongly agree with what I have said.
The patent on Mr. Berning's "Output Transformerless Amplifier Impedance Matching Apparatus" can be found here (although it addresses a push-pull version rather than the SET version). In the first figure note all of the "stuff" between the output tube and the "load" (i.e., the speaker), including a transformer and numerous solid state devices. And note in the introductory text:
A linear audio amplifier includes a push-pull pair of vacuum tubes operating in a linear amplification mode coupled through a pair of dc-dc switching power converters to an external load impedance. Each power converter includes a transformer with one or more secondary windings that drive rectifier circuits, and the resultant dc voltage sources are loaded by their respective tubes.... The effective turns ratio between primary and secondary windings of these converter transformers determine the voltage/current step-up/step-down relationships between the tubes and the external load impedance.The last sentence is identically applicable to any conventionally designed tube amp that has an output transformer. (Although in both cases it is the voltage that is stepped down and the current that is stepped up, rather than the opposite which is what the wording of the sentence might seem to suggest).
Best regards,
-- Al