45 Type Push/Pull

Just remembered that I have heard the VAC Renaissance amplifiers which are DHT push pull.It's been quite a while but I really liked what I heard from them.
Regards,

subtle push-pull crossover notch grunge

This is something that should not happen with a DHT p-p design. Crossover or notch distortion are artifacts of transistors and designs that are not class A, unless there is a serious design defect.

I have a pair of type-45 amps that I have been playing at home for several years. They started as 45 SETs, but on examination of the internal circuit it was obvious they were candidates for improvement in the wiring, parts and input circuitry.

With each update the amps sounded better- more detailed, smoother sound, etc. Ultimately I pushed them to a P-P design and the improvement over the SET version was dramatic! I think they can be improved further, but its been convincing enough that I just play them for the most part.

Phil (213cobra)
You raise an interesting point, the quality of the output transformer and power supply are so critical to what you'll hear with a SET.Get those done to a high standard and sit back and enjoy. Compromise with those aspects and you will never know the full potential of this type of amplifier. It's true for all topologies but seems more so for the SET.

>>This is something that should not happen with a DHT p-p design.<<

Yup. Assuming push-pull class A. But what about Class AB p-p designs using triode power tubes, or for that matter p-p voltage amplification sections using small signal triodes. A push pull design *can* forego notch grunge but not every designer elects to.

DeHavilland made a 75w triode push-pull amp built around a pair of 572 tubes. It was confusingly described as "100% pure Class A A/B." We see today an increasing number of push-pull triode amps with power ratings well above what could be expected from Class A push-pull and one of the effects is that they sound like Class AB amps and sometimes like Class AB amps that use tetrodes or pentodes. What's good for guitar amps (biasing AB toward B for sparkle) doesn't always benefit hifi.

Phil

Phil, even if you run class AB1, you still don't run the risk of any crossover artifact, since at lower power levels where the crossover artifact might occur, the tubes are in the A region.

What I have found is this is more a problem relating to solid state than tubes, on account of how the output transistors are biased. In tubes, in only seems to show up if there is a malfunction or design defect.

IMO this is a very common myth! However, that is not to say that an SET does not have certain desirable qualities. Chief amoungst them is the ability to have distortion linearly drop to zero as power is decreased. This is where SETs get their 'inner detail' they are known so well for.

Most phase inverters in P-P designs introduce their own kind of harmonic distortion (having nothing to do though with crossover distortions). It is this additional harmonic distortion that causes P-P amps to often have increasing distortion below a certain low power level. It can be designed out by avoiding the use of stand-alone phase splitter circuits- by instead integrating the phase splitter function right into the voltage amplifier stage. This eliminates the need for a separate circuit and the less signal process the better (IMO). Traditionally the best way to do this is with a differential amplifier for the voltage amp.