[patrick-turner]

On Tuesday, 12 November 2013 20:40:29 UTC+11, John L Stewart wrote:
Here is something to puzzle over in your quitter moments! Cheers to all, John L Stewart +-------------------------------------------------------------------+ |Filename: Triode UL.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=361| +-------------------------------------------------------------------+ -- John L Stewart

Doug asked, in so many words, "have ya built it?"

Anyway I doubt it has much in common with any UL circuit where the screens of OP tetrodes or pentodes have a fraction of the anode signal voltage applied so that the OP tubes get a fraction of the NFB that is available in a full triode connection or a real triode without a screen.

The Schematic JS tenders to us has ONLY triodes used. There are "UL taps" on OPT which feed the anodes of the driver triodes with cathodes direct coupled to OP triode grids.
Of course one would have to bias the secondary of IST and do other things to make the circuit shown more than a smoke producung tube buster.

But ANYWAY, the OPT primary "UL taps" provide some NFB shunt FB to the signal applied to the OP tube grids via the Ra of driver tubes, and field effect of anodes on electron flow. But I doubt the amount of NFB is effective enough to make it worthwhile to hurry to the patent office, even if you could travel back to 1946 when patenting some desirable gadget was like printing money in your shed legally.

The thing about *most* output triodes is that they have been designed to be easily drivable with most loads, typically needing between 20Vac and 50Vac and having gain of about 3.5 to 6 while having Ra low enough to always be usefully lower than the anode load, thus ensuring a good damping factor, and all manner of trickery such as UL connections and pentodes, tetrodes and cathode are not needed if it is found the triodes give sufficient power.

A normal triode amp with pair of trioded KT66/6L6/EL34/KT88/KT120/6550/KT90 or real triodes 300B driving RLa-a 10k0 in class A is a kind of gold standard. There are easier ways to effectively apply NFB than using an IST and FB via UL taps, and anodes to OP tubes.

But I could be wrong.

Where are all the working voltages and Vdc, Idc RL values et all? I would ask "where are all the details of circuit operation including distortion measurements and what is bandwidth, stability, and R-out, etc, etc, etc?"

Of couse JS probably would need to spend a day or three wiring it and testing it.
He should have the time with snow now laying around his house and too cold to ride a bike anywhere.

I'm up to my neck in keep busy doings, so I won't be trying JS's schematic.

Patrick Turner.