Strange input stage/phase inverter

[jcalvarez]

Hello!
I have seen the following circuit in "Acrosound_Ultra-Linear_Transformers_1955_gc.pdf" as part of a 100W PP amp example. What are the advantages (if any) against a more conventional one?

Simulation works. There is a balancing resistor between R4 and R3, omitted for simplicity.
Thank you!
Jose

 

[JonSnell Electronic]

First glance, U3 does nothing but hold a steady voltage on R3 .
U1 is just a buffer and U2 does all the work.
No advantage on standard double triodes.

 

[baudouin0]

How well balanced are the outputs?

 

[jcalvarez]

First glance, U3 does nothing but hold a steady voltage on R3 .
U1 is just a buffer and U2 does all the work.
No advantage on standard double triodes.

In the amp is used as GNF input.

 

[jcalvarez]

How well balanced are the outputs?

Not perfect:

 

[jcalvarez]

I just got interested because I have never seen such a circuit before.

 

[rayma]

Originally used in oscilloscopes, this is a cross-coupled phase inverter, also used by Audio Research
as a balanced driver stage (with cathode follower outputs and current source load) in their earlier amplifiers.

 

[jcalvarez]

Originally used in oscilloscopes, this is a cross-coupled phase inverter, also used by Audio Research
as a balanced driver stage (with cathode follower outputs and current source load) in their earlier amplifiers.

Got a headache trying to follow that circuit, thanks for that 🙂

 

[directdriver]

It's a Van Scoyoc phase splitter.

 

[jcalvarez]

It's a Van Scoyoc phase splitter.

Thank you, it will be an interesting read.

 

[smoking-amp]

I count six tube elements used for the inverter in that AR amplifier. Obtuse.

 

[directdriver]

I count six tube elements used for the inverter in that AR amplifier. Obtuse.

ALL of Bill Johnson's phase inverter uses a perverse version of the floating pharaphase inverter in front of all the symmetrical cross-coupling input to driver to output stages. So unnecessarily complicated. Count them, there are 12 tubes before the output stage!

 

[6A3sUMMER]

Does anything exist that can not be made more complex.
Point of diminishing returns? lower reliability? etc.

"You should make things as simple as possible, but no simpler" Albert Einstein
Just my opinion too.

 

[PRR]

Every tube-geek should sleep on copies of Radiotron Designer's Handbook. The small black edition in even years, the big red edition in odd years. RDH answers most all basic test and topology questions.

The 3rd has all you really need but the 4th has the wonky stuff. In the 4th (red), "Exciting push-pull amplifiers" starts page 521. The Van Scoyoc is mentioned as a footnote to page 527, note C25. Sadly it is not in the general Radio-News but a supplement for selected readers.