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Is Western Electric selling a Push-Pull amplifier (91E) as a Singlended ?

SIY

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OK, looked again, and skimmed the Tube CAD Journal article. I had not heard of TCJ, but had heard of John Broskie, though forgot he lived just a couple of hours (more like three now, traffic) north of me. Don't know him at all, just by reputation. Wish TCJ had been around back when I was actually trying to design tube circuits. Mostly preamps, though; aside from some conventional designs, my only unconventional (direct-coupled, OTL) tube amp worked fairly well -- until it failed spectacularly.

My excuse is that I've been peering at some feed-forward stuff just for fun, using dynamic current dumping to enhance the output slew rate, but all I can say is "brain fart" when looking again at the schematic. Duh. Keeps me humble, hopefully. I would've expected them to just split the input signal off to the top device instead of mirroring it around (sort-of) and needing the N-FET, and also imagine the toroidal transformer hits the latest audiophile buzz-words better than a typical EI gapped transformer with the B+ routed through it conventionally'ish. This thing looks like it was invented mostly to give the appearance (but not the fact) of a single-ended tube design, with a patent thrown in for good measure because most of us probably wouldn't do it that way (for good reason). Must be large degeneration Rs to keep the thing marginally stable without bias drifting all over...

But, it's pretty... :cool:

Edit: TCJ's front page had a link to "DVC" that I had to click to see what that meant... My first subwoofer was a servo design using a dual voice coil woofer from an Infinity IRS, using the second coil for feedback. The actual speaker used an asymmetric crossover, Arny's design I think, pretty much as John described. Sharp cookies, them guys!
If you get a chance to hang out with John, it's a lot of fun. I would encourage it. We first met at a conference in Germany and had a blast.

Yes, the more you look at the circuit, the more it seems to be a commercial exercise. Seeing "Western Electric" as a brand now reminds me much of seeing a classic rock act, there are no original members, and the only person who ever actually played in the band was their fourth or fifth bassist, but someone owns the group's name.
 

KSTR

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If the plate load (without OPT+sec.load) were just a resistor, we would agree on SE operation.
If the plate load were basically a DC resistor and AC current source (choke load), same.
If the plate load were a DC and AC constant current source (MOSFET plain current source), same.

In the way I see it, the plate load now is basically a large but negative-valued resistor (AC+DC current souce inversely modulated with the voltage across itself: more voltage, less current), then... still visually a SE concept in my book because the topology change from constant current source to what we have here is only minimal.

Of course we can argue that any plate load that has an active character, realizing conditions not achievable even in theory with only passive parts, will render an output stage as non-single-ended. The constant current source condition is the corner case here, as it requires theoretically infinite supply voltage and infinite resistance when to be realized passively.

That emulated negative resistance plate load creates an unusual slightly upward sloping open-load loadline operation (but we cannot go any steeper than the triode's output lines, obiously).

This tilts the final AC loadline with OPT load less downward, it becomes flatter. As does a reactive load-ellipse. Voltage gain increases as this is slightly positive feedback in the end. Not clear what it does to distortion but it might really be somewhat lower...
 
OP
Balle Clorin

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Maybe you should get an Electrical Engineering degree so you could reason this out for yourself as opposed to trusting Tubecad over WE.
But I also wouldn't trust any tube amp to be high fidelity in this day and
Maybe you should get an Electrical Engineering degree so you could reason this out for yourself as opposed to trusting Tubecad over WE.
But I also wouldn't trust any tube amp to be high fidelity in this day and age.
Hmm ? Did I step on some sore toes here?
Well I only have a Master in Chemical Engineering , but have built tube amplifiers and read schematics and simulated (LtSpice) the circuits the last 20 years. I have no problems understanding Tubecads schematic and written text about electronics, So I found his article excellent, and it uncovers Western Electrics sales talk. That should be interesting information to many.So I posted it here in a polite way I think.

I think you would be less upset if you did understand the Tubecad text and schematic better.( Or maybe even more upset.?)

The information to learn and understand electronics is readily available for anyone who wants to. With electrical degrees or not. It does not make amateurs into professors but I think It gives an understanding and adds an extra dimension to the hifi hobby to know what is going on inside. But that is me…
 
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Balle Clorin

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Something sent wrong in the editing above, I blame the electronics…
 

Prana Ferox

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It is an interesting discussion but this all sounds like a whole lot of consternation for something which charitably is purchased as furniture and not electronics.

I know there's another thread on this but I still find the revival of this brand bizarre and a bit gross.
 
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Balle Clorin

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Full set of measurments in the November Stereophile issue.

1% distortion at 1.8watt in 8ohm, 5w in 4ohm. Powerful stuff indeed, no mentioning the fact that it is NOT a single ended design.
 

sarumbear

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Take a look at this.. Makes me wonder if not the buyers are mislead by the selling arguments...at a quite high price.
Do they understand what they are getting? Not a Single ended 300B triode, but a push-pull amplifier consisting of a Mosfet and 300B triode in combination..
Would they buy it then?


WE:
  • The Western Electric Type 91E is a Class A, single-ended (SE), integrated amplifier for high-fidelity audio reproduction.
A WE quote from 2018 posted on AudioAsylum... "In addition to announcing the availability of the 300B, I'd like to share some of our adventures in product development. Continuing our 80th anniversary celebration of the 300B, we are unveiling a new single-ended amplifier called the 91E, as an homage to its famous predecessor the 91A, first introduced in 1936. The 91E embodies a new proprietary Class A2 parallel feed current source topology (patent pending), combined with toroidal output transformers, and microprocessor controlled automatic bias. It will achieve in excess of twenty watts per channel-a never before realized level of performance for the 300B in a single-ended circuit."
View attachment 223450

And the evaluation of the patented circuit here by TubeCad.
Patent here

From Tube CAD:"It certainly looks unconventional, but is its operation as unconventional as its appearance? First, let's add some signal relationships throughout the circuit.

Steered%20Current%20Source%20for%20%27Single-Ended%27%20Class-A%20Amplifier%20with%20Signals.png

The triode receives the input signal at its grid. As the signal swings positively, the triode increases its current conduction and its plate voltage is pulled down, which then pulls down N-channel MOSFET Q2's source voltage, which in turn provokes a decrease in the voltage drop across its drain resistor, making P-channel MOSFET Q1 draw less current. When the input signal swings negatively, the opposite occurs; the triode draws less current and MOSFET Q1 draws more current, pulling the triode's plate voltage up. The capacitor coupled output transformer relays this amplified signal to the loudspeaker. In short, push-pull operation, not single-ended functioning, as MOSFET Q1 actively varies its current flow match the triode in anti-phase, just like every other push-pull output stage.

Parafeed%20Topology%20Example%201.png

The patent claims that this a para-feed arrangement, but really is just a push-pull totem-pole arrangement of dissimilar output devices with a coupling capacitor attaching to the output transformer's primary, which allows us to use a non-air-gapped output transformer. In fact, we could just as easily use a bipolar power supply and DC coupled the output transformer primary at one end and ground the other end."
That is variable voltage single ended circuit. Push-pull means both cycles are manipulated by input signal. This circuit only changes the voltage of a single ended amplifier.
 

Sal1950

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Full set of measurments in the November Stereophile issue.

1% distortion at 1.8watt in 8ohm, 5w in 4ohm. Powerful stuff indeed, no mentioning the fact that it is NOT a single ended design.
But it sure is purdy! :)
 

fpitas

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It is an interesting discussion but this all sounds like a whole lot of consternation for something which charitably is purchased as furniture and not electronics.

I know there's another thread on this but I still find the revival of this brand bizarre and a bit gross.
I think it's humorous in a sad way. I'm sure the WE engineers would wonder who in their right mind wanted a single-ended design, and the attendant distortion. Obviously nostalgia doesn't have to make sense, just dollars.
 

GXAlan

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Full review has been published for free

I wonder how it sounds. It may very well be that the threshold of audibility is met with this amp, given that it’s noise performance is far better than it’s THD and we are more sensitive to noise.
 

fpitas

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Full review has been published for free

I wonder how it sounds. It may very well be that the threshold of audibility is met with this amp, given that it’s noise performance is far better than it’s THD and we are more sensitive to noise.
As long as you don't feed it real complex music, it might be OK. But I bet the intermod gets special in a hurry if there are lots of layers.
 
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