Ah I see... somebody somewhere once used valves and transistors together for a completely different reason in an unrelated field so therefore ALL hybrid solutions have "all been done before"

Actually it may well be unique (or not!) the way I've done it here and the output stage has a couple of twists to it that make it a potentially new topology.... depending on how much a known topology must be modified before it is considered new of course!
I'm sure that in this day and age absolutely any "advance" in pretty much anything analogue and especially the dying hobby of hi fi would be greeted by the wider world with the same enthusiasm as a newly invented and improved steam regulator for the likes of "The Flying Scotsman"
Oh and if knowledge IS shared then it is no longer proprietary and can no longer be copyrighted etc. I do run a business and
may at some time want to build some of these for sale... or at least something related to this incorporating things I've learned from this prototype.
My purpose in starting the thread (and I hope I will be forgiven a little hubris) is that after designing and building something like a hi fi amplifier and getting it working well I just wanted to share some of the excitement and sense of achievement over "my new baby"

No doubt exactly as a man having just completed a scale model of the Eiffel Tower from matchsticks would likely feel like sharing this with other modellers on an appropriate forum

or like someone who has just built a diy variable loudness control for his Quad 909 may want to tell others how well it works on a hi fi forum
I had thought of designing my own Loudness Control - well modified to suit what I saw as being a problem. The enthusiasm is still there, but Arthritis in my hands means, any soldering I do looks like to has been done by a Welder

. Plus, my eyes are shot to bits, so I would probably solder something else lying on the bench, rather than the bit I am supposed to


.
Plus, what I did, hardly qualifies as a design - a small mod to an pre-designed Band-stop Filter Network - by removing capacitors from it, which resulted in treble frequencies suffering the same attenuation as the mid-range stop - band. It works, but without a signal generator or my Spectrum Analyzer, I have to rely upon "Subjective Listening Tests". In this regard, I don't have the same confidence as Jez. But it seems to be effective and after all, at normal listening levels, it it "Out - of - Circuit".
Further to the above, my 909, Sugden and Spendors are stock items - none of which are currently in production. So the pleasure I get is from exploiting the performance of the Spendors, which although very good, I never appreciated "Just how good". This is by way of what are now two geriatric amplifiers.
Whilst my Sugden is currently unused; and in truth I bought it purely on reputation and experience of my first Sugden, all those years ago, the 909 has been subjected to some fair listening tests. It too however, was bought on the speculative argument that it would operate wholly in Class A at the levels I wanted to use it - low level.
That aside, it is proving to be an astoundingly good purchase. I won't use the term muscle although it most certainly can provide it. The term "Weight" is more appropriate as it gives a solidity to the sound-stage, which I have rarely heard outside of a concert hall - despite the low level it is operating at. Whilst having enjoyed my 303 for some 50 years and my 405 for 20 years - the 405 being a brilliant design, I did not appreciate just what a step - up the 909 is. Truly, wonderfully precise - arrogant even, in the way it deals with complex music. Well done Quad.
I appreciate my Stax much more now too, although listening to my son's Hifiman's "Planar's", may well super-sede them. I didn't get much time to listen to them when we were visiting him, but as he will be down in August, a decent session should provide some answers. Even so, driven by the 909, the Stax seem to come alive as they can handle more drive than my Spendors and being single Electrostatic Elements, the transition across the musical spectrum is seamless, a function of both the 909's frequency response, sustained power level, relative to where the music is (bass, mid-range or high frequency) - and zero phase delay due to absence of crossover network, transition points.
Jez makes the point about well designed amplifiers, with good figures not sounding too good. Well, the parameter which was most important when matching amplifiers to loads is always "Return - Loss". An amplifier with an excellent Damping Factor is only one half of the equation. If the return loss of a loudspeaker is poor, it will have a great impact on the output stages of an amplifier and "That" would certainly show up in listening tests. The original Quad Electrostatic loudspeaker was "full - range". That in itself is enough to set it greatly apart from any loudspeaker of its day and is probably still true of many modern loudspeakers. To design a Phase - linear Cross-over Network is both expensive, a fundamental compromise and a pain in the arse. And they will always be load - conscious. "The Loudspeaker is the load for the Amplifier". But equally true, "The Amplifier is the load for the Loudspeaker". Mis-match a valve amplifier into a load and you will burn out the output valves. But, before it goes "Pop", you will hear the consequences of that mis-match.