Pros and cons of valve amps

[anthonyTD]

Something I meant to comment on at the time but forgot.
If you check out the original GEC 100 Watt Circuit,http://www.oestex.com/tubes/Circuits/GEC100w.gif using a pair of KT88's you will notice that it uses no over-all feedback at all, however; its ouput stage is ultra-linear configured.
I have actualy heard a completed stereo version of this amp [I supplied the chassis]and it works very well considering.

One would never use a tetrode or pentode amp without negative feedback as it would then be a current source and have no damping factor at all. With low-ish feedback this effect will come into play to an extent of course, which is what I was getting at. Even with triodes and zero feedback it will happen to an extent. The degree to which power rises with increased load impedance is far less though than the amount it will increase with falling load impedance with a SS amp. Unless you deliberately make the valve amp a current source as in your example but this is completely undesirable in any amplifier and would never be done in practice.

[Arkless Electronics]

Something I meant to comment on at the time but forgot.
If you check out the original GEC 100 Watt Circuit,http://www.oestex.com/tubes/Circuits/GEC100w.gif using a pair of KT88's you will notice that it uses no over-all feedback at all, however; its ouput stage is ultra-linear configured.
I have actualy heard a completed stereo version of this amp [I supplied the chassis]and it works very well considering.

We were already in agreement over UL of course....
I have an original copy of the GEC amplifiers pamphlet that I ordered from the factory when I was about 13!

[spendorman]

This looks interesting:

https://youtu.be/BnR_DLd1PDI

[montesquieu]

Some oddball designs by Time de Paravicini fall in this category as well .. EAR 861, push pull EL519s, no global negative feedback, supposedly pure Class A (presumably up to the distortion specs at least), uses 'Enhanced Triode Mode' (whatever that is - maybe some variant of ultralinear?) and a custom 'quadrafillar' output transformer. I have to say its performance with my current-hungry Tannoys was pretty outstanding even with a meagre 32 watts, pretty close to what my PP KT88-specced (KT90-equipped) Radford STA100 manages.

[walpurgis]

I have a friend who uses an EAR 861 to drive Tannoys. It's a very nice sounding amp.

Although he does like his Monarchy Audio SM-70 Pro just as much.

[Arkless Electronics]

Some oddball designs by Time de Paravicini fall in this category as well .. EAR 861, push pull EL519s, no global negative feedback, supposedly pure Class A (presumably up to the distortion specs at least), uses 'Enhanced Triode Mode' (whatever that is - maybe some variant of ultralinear?) and a custom 'quadrafillar' output transformer. I have to say its performance with my current-hungry Tannoys was pretty outstanding even with a meagre 32 watts, pretty close to what my PP KT88-specced (KT90-equipped) Radford STA100 manages.

If it's anything like the EAR 509, 519 and lots of other TdP designs then it's pretty much the opposite of your description! They are certainly unusual though yes. There are several feedback loops but non from the secondary of the OPT. It has UL taps from OPT to screen grids, cathode windings a la Quad II and Mcintosh and then the anodes of one phase are cross-coupled to the cathodes of the other by electrolytic caps.. other taps bootstrap the driver stage and another winding is used just to provide balanced feedback to the cathodes of the driver stage and globally(ish) to the input stage.

It's pretty clever stuff and they usually both sound and measure very good. I got to know Tim a bit when working for MF and then Alchemist.. an interesting bloke.

I'll bet not many remember the Michaelson Audio Chronos pre and power? A few may with the incredibly unreliable Odysseus

[montesquieu]

If it's anything like the EAR 509, 519 and lots of other TdP designs then it's pretty much the opposite of your description! They are certainly unusual though yes. There are several feedback loops but non from the secondary of the OPT. It has UL taps from OPT to screen grids, cathode windings a la Quad II and Mcintosh and then the anodes of one phase are cross-coupled to the cathodes of the other by electrolytic caps.. other taps bootstrap the driver stage and another winding is used just to provide balanced feedback to the cathodes of the driver stage and globally(ish) to the input stage.

It's pretty clever stuff and they usually both sound and measure very good. I got to know Tim a bit when working for MF and then Alchemist.. an interesting bloke.

I'll bet not many remember the Michaelson Audio Chronos pre and power? A few may with the incredibly unreliable Odysseus

Interesting to hear a professional's opinion ... I've generally liked his stuff a lot and have I've owned a bit of his gear - 509 monoblocks (the only one of his I found a bit 'meh' TBH), V20 (loved that especially after having some decent componets swapped out for the basic stuff it had in), 899 (also the Actue CD and MC3 SUT), also heard a fair few as well, the best of which was the 534 ... to my ears the 861 was the best of the lot. Also had an Odysseus yonks ago ... mechanical hum drove me potty but it was actually a nice performer. Didn't have it long enough for it to break down though ...

[Arkless Electronics]

Interesting to hear a professional's opinion ... I've generally liked his stuff a lot and have I've owned a bit of his gear - 509 monoblocks (the only one of his I found a bit 'meh' TBH), V20 (loved that especially after having some decent componets swapped out for the basic stuff it had in), 899 (also the Actue CD and MC3 SUT), also heard a fair few as well, the best of which was the 534 ... to my ears the 861 was the best of the lot. Also had an Odysseus yonks ago ... mechanical hum drove me potty but it was actually a nice performer. Didn't have it long enough for it to break down though ...

Odysseus sounded great but Anthony Michaelson wouldn't listen to me about the issues with cheap under-rated parts in it and rejected my internal report on the matter... After he'd asked me to write it... virtually all of them blew up within a few months of being sold! Tim re-released the design under his EAR brand and with all the issues sorted

[anthonyTD]

We were already in agreement over UL of course....
I have an original copy of the GEC amplifiers pamphlet that I ordered from the factory when I was about 13!

[anthonyTD]

From what I remembered at the time, the original control grid was strapped to the Cathode, and the Screen grid was then used as the control grid!

'Enhanced Triode Mode' (whatever that is - maybe some variant of ultralinear?) and a custom 'quadrafillar' output transformer. I have to say its performance with my current-hungry Tannoys was pretty outstanding even with a meagre 32 watts, pretty close to what my PP KT88-specced (KT90-equipped) Radford STA100 manages.