Quote:
Originally Posted by 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.
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Hey Patrick, you can do better than that! You actually touched on the reason that circuit does what it does in your response. And I’m surprised that Phil has not chimed in with his ideas.
Here is a hint to give you a lead to the operation of the circuit. You can find enough information in the RCA Tube Manual RC-14 to get you going. Don’t think you will find much to help in RDH4.
The IST has nothing to do with the circuit other then as a phase invertor. It will run well from any common power amp front end. Even your favourite. So go back & take another look!
Not much biking these days, altho I got out for a little more than 50 km yesterday. Busy with the log splitter & otherwise getting the place ready for winter. I will soon trade the bike for skis. The weather to turn cold & snow this week.
Not much electronix this summer either. Lots of yard work on 4 ½ acres. Had to chop up five large trees that came down in storms. And the electrical boxes I put way out in the yard after 35 years the wood was shot. I put 110/220 volts underground the full length of the property when we built here. Very handy, but lots to repair as everything seems to wear out. Me too!!
In the meantime, here is something else to get your mind around.
Cheers to all, John