Is a pentode PI the Power Scaling solution?

[Mickey_C]

Has anybody used pentodes in the phase inverter?

Could a long tail pair be built with a pair of them, that sounds like a 12AX7 PI? Any dual pentode tubes that would be suitable for a one tube solution?

I've been contemplating TUT4 chapter 6 for sometime, namely the section on controlling pentode tube current and disipation via the screen grid. Imagine an amp where the power tubes are power scaled along with the PI screens (if they're pentodes).

Would this give us our goal of PS the output tubes without needing a limit/compensation control?

Just thinking/sharing out loud.

[stoo]

Is that much different than just varying the plate voltage on the triodes along with the B+ on the op tubes? I do like your idea though!
Stew

[klingo]

hi!
quad II, kt66 drived by two ef86(in pentode) PI with gain but ultralinear KT66 with cathode in the primary winding...
or you may consider williamson topology...a split-load PI in dual small pentodes and then the big bottles...
i don't know about dual pentode in a single glass but you could use triode/pentode noval like ecf/ecl82..86..a triode first stage, triode cathodyne PI, the two pentode PP driving the big one's... and little neg feedback because NFB input is a bit far away from OT (phase shift/IM dist)
no idea if this will sound good! but if you find a way to power-scale an amp(in a realistic way) please tell us!
sorry for froggenglish
olivier

[stoo]

I wonder if you could use like an Ef86 in the PI where the Plate and cathode resistors are the same value and the two feeds to the PI are taken from the plate and cathode? (forgot what they call this config?)
Could you then vary the screen voltage to affect gain?
Stew

[Alexo]

Are you talking about using a remote cutoff pentode like an EF183?

[David Root]

It's interesting indeed but if it were the answer I think Kevin O'Connor might be using it himself by now.

The cathode with its own primary winding is indeed a proven design. IIRC the famous McIntosh OT used that to great effect in conjunction with UL operation. If I ever do an audio design I will start with the Quad II, Williamson and McIntosh. Only problem is you have to have a custom OT built.