[Eeyore]

With my interest in toobie stuff revitalised, I've had a few ideas that strike
me as rather interesting. I'll elaborate at length later.

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

The objective btw is super-linear triode stage.

Graham

[Eeyore]

Bret Ludwig wrote:

Eeyore wrote:
With my interest in toobie stuff revitalised, I've had a few ideas that strike
me as rather interesting. I'll elaborate at length later.

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

The objective btw is super-linear triode stage.

Many such hybrid circuits exist and perform well. They sell poorly and
are often intolerant of amateur fumbling and tinkering.

What's the rationale behind selling poorly ?

And where do you reckon the amateurs screw up with them ?


Graham

[Chris Hornbeck]

On Sat, 09 Dec 2006 01:58:54 +0000, Eeyore
wrote:

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Hybrids are burdened by history. Many early attempts
included deadly combinations of ignorance of device
physical limitations, especially under transient or
fault conditions, and ignorance of the particular
advantages of valves, leading to some misappropriate
use of semiconductors.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

Strangely, I've been working on a valve current mirror
using some proprietary positron valves. Kinda attacking
the same problem from the other end. Arf!

The objective btw is super-linear triode stage.

For a super-linear triode stage, simply provide a
high impedance load to a good (the Telefunken brand,
early Amperex, or the older American large structure
devices give best results, but device type gives
enough spec to maintain interest) type 12AX7/ECC83
valve at 150 anode volts and somewhere between a half
and a milliAmp standing anode current.

Off the shelf parts give THD numbers better than 80dB
down at outputs on the order of +10dBU or even larger.
The best devices give numbers 10dB better still. I know
of no semiconductor device that can approach with 15dB
of the intrinsic linearity a garden variety 12AX7.

Another interesting device is the 5687. Well worth
examining.

All good fortune,

Chris Hornbeck
"Too soon oldt; too late schmardt."

[Patrick Turner]

Eeyore wrote:

With my interest in toobie stuff revitalised, I've had a few ideas that strike
me as rather interesting. I'll elaborate at length later.

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

The objective btw is super-linear triode stage.

Graham

I use bjt based CCS routinely for common cathode CCS,
and for dc anode feed to input tubes or preamp tubes.

The reduction of load current change with triodes means that THD/IMD is
all reduced
without external loop FB, and gain is optimized, and the B+ can be lower
or tailored to have the dc higher than one would with R.
R usually must be 4 x Ra, which means to get a wanted dc flow the B+ may
have to be twice the
supply value where a CCS could be used.


In the case of the CCS, the action of the bjt is virtually passive,
since the bjt does
nothing except provide a constant flow of current regardless of
frequency between say dc and
500kHz, OK for audio apps.

This allows the triode to get on with business without powering what
is often a low value of resistor just to get dc to the anode; such
regular resistance as the dc supply element is very primitive
engineering,
and does not sound as well as CCS.
Chokes with a series R can also act very much better than any simple
resistor.


And I also like the occasional J-fet used as an input device for low
noise
which is usually at least 20dB lower than any 12AX7 in a phono stage.

Patrick Turner.

[Patrick Turner]

flipper wrote:

On Sat, 09 Dec 2006 01:58:54 +0000, Eeyore
wrote:

With my interest in toobie stuff revitalised, I've had a few ideas that strike
me as rather interesting. I'll elaborate at length later.

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

The objective btw is super-linear triode stage.

Graham

Heresy! Heresy!

Or at least that's what say when I do it

Near as I can tell there are different 'levels of acceptance'. Purist
purists don't use SS.

Purists therefore prevent themselves hearing music
with as little as possible Noise & Distortions.

Nothing wrong with staying with resistance loads and tubed CCS,
and tubes only for inputs on phono amps but the price to be paid
is that the tubes cannot shine as well as thay can when not supported
by willing SS slaves working uncomplainingly and without any
measurable signal effects except reduction of N&D without using
loop FB.

But look, anything goes, really, let us not be de-facto members of the
anti novel circuit topology Gestapo.

The proviso is merely whether it is acceptable i the ears of the
listener.

Use tubes and OPT and bjt input stages, or tube input stages and
bjt/mosfet output stages;
whatever is done should be done with conviction and logic and verve.

There should be no penalty for whatever one does, and the ultimate
alternative to tubes is to
ban them altogether and do an all SS circuit, with PWM, otherwise called
a digital amp,
and these look set to topple class AB SS amps off the pedestal they sit
upon.
Soon all the major brands will promote PWM because its cheaper and
easier to make.

But not for the DIYer, who would surely struggle with such gee-wizery.
Remember when CD players and the CD was launched?
I don't recall a single account of anyone building a transport and DA
converter from basic building blocks of discrete opamps, bjts, fets, R
,L & C.
99% of the audio fraternity just copped it sweet.

Vinyl when its good is bleedin fantastic and will compete with the best
digital,
probably because the formats have capability to produce technical
results
far better than our ears can measure. R2R pre-recorded 1/4" tape was
even better than vinyl
and some guys did make their own rerplay machines, but not many.
Anyway, the point I make is that the state of the art in amp design is
only a state of the art,
or more precisely the state of the science.
The status quo state of the science in audio has been capable of
flawless audio reproduction for about 50 years now.
The scope for innovation with hybrid designs in the latest PWM circuitry
is about zero.
The pcb boards must be extremely crammed with SMD which are so very
easily made by robots
so that the speed of the switching is possible and any other way of
doing things just won't work.
Trying to add tubes into a PWM "digital" amp would to me seem quite
fruitless,
but I have not tried it and the number of tubes needed could be
horrendous,
so lets not make the greenhopuse effect any worse than it need be.


Tube use in analog amps will remain, despite the digital onslaught and
SS lover brigade's attacks.



Then there's, well, ok in the power supply.

The most common acceptance seems to be: as long as it's 'not in the
signal path'; with that definition being a bit floppy sloppy depending
on how you define 'signal path' since, if you're persnickety about it,
just about everything can be considered in the signal path one way or
the other. At any rate, that appears to extend to constant current
sources.

Past there it starts getting controversial. Some people, of which I am
a member, consider MOSFET followers ok. I don't know if there's an
'official' rationale behind that so I invented my own: not doing gain
itself (as you suggested).

Which, conveniently, allows current mirrors and I've played around
with those quite a bit with one being my cathode current mirror on PP
output tubes to force bias matching so no DC offset in the OPT (falls
within the 'not in signal path' criteria). Another is reflecting
current into the load, which increases gain because plate is fixed at
B+, and that led to my current mirror phase splitter. My "Looking
Glass" amp is a current mirror PP design using all the above.

Stick enough in and it's a 'hybrid'. My 'PC Speaker amp' is a low
voltage 6GM8 and current mirror hybrid.

I've also played with a high gain mirror topology I call "current
loop." Got a voltage gain of 328 out of a 6GM8 that way.

I'll be interested to see how you improve linearity with a current
mirror.

PSU rail supplies are always effectively in series with the device
output signals.
Quad II had horrendous hum levels at the CT of their OPT.
the N&D caused by Quad's crummy PSU was about the same as the N&D
generated by the tubes themselves,
and not at detectably objectionable levels at a watt of output into
rated class A loads.

But for those who accept class AB and want greater untroubled technical
performance,
and, dare I say, better sounding music, then don't emulate Quad's bean
counter driven miserly
approach to PSU methods.
Use some SS diodes and big caps and the music just gets better IMHO.


Patrick Turner.

[tubegarden]

Hi Graham and RATs!

I am not a purist. Purile, perhaps, but, I just play with tubes because
I understand almost enough to be dangerous. It keeps my mind and hands
active the few hours a month I am capable of sitting up and swearinq,
er, soldering.

I enjoy reading John Broskie's web magazine. But, my mind trips,
stumbles and falls on his SS stuff. I am too old and sick and lazy to
try and learn. I was able to spot the good idea in Blumlein's garter
circuit and implement it in a real amp. It sounds fine. I don't measure
stuff anymore. I may send it home with my visiting Guru next week for a
go on his AP system.

My older, cruder performance measurement tools haven't been powered up
for many years. I like listening to Music. Playing engineer nerd takes
more energy than I have, very often, so, I just do what I can

Happy Ears!
Al

[Ruud Broens]

"flipper" wrote in message
...
: On 9 Dec 2006 10:40:37 -0800, "tubegarden" wrote:
:
: Hi Graham and RATs!
:
: I am not a purist. Purile, perhaps, but, I just play with tubes because
: I understand almost enough to be dangerous. It keeps my mind and hands
: active the few hours a month I am capable of sitting up and swearinq,
: er, soldering.
:
: LOL. Yeah, I enjoy the swearing, uh soldering, too.
:
: I enjoy reading John Broskie's web magazine.
:
: A veritable gold mine. And he writes well too.
:
: But, my mind trips,
: stumbles and falls on his SS stuff. I am too old and sick and lazy to
: try and learn. I was able to spot the good idea in Blumlein's garter
: circuit and implement it in a real amp. It sounds fine. I don't measure
: stuff anymore. I may send it home with my visiting Guru next week for a
: go on his AP system.
:
: I also like playing with the SS stuff. My next one will have an opamp
: auto balance for the PP tubes.
:
: My older, cruder performance measurement tools haven't been powered up
: for many years. I like listening to Music. Playing engineer nerd takes
: more energy than I have, very often, so, I just do what I can
:
: I know what you mean. Call me silly, and it is. I don't know why but I
: get all oogly googly just seeing 'em lit up. Solid state just sits
: there, dumb and dark.
:
: It's *fun*. Built the little guitar amp literally from junk box parts
: and clever whiz that I am included a line input too so it's in the
: corner playing Beethoven's 5'th as I type. Ok, the power transformer
: as OPT isn't going to get into Broskie's Mag but hey, it's a GUITAR
: amp. And it glows
:
: Besides, the nephew thinks it's slicker than snot on glass and since I
: built it I'm now at least on a par with Montgomery Scott, aka Scotty
: the miracle worker, in his eyes and I didn't have to hit Warp 6.
:
: Hey, don't tell anybody but I crammed a MOSFET follower in there to
: save a bottle.
:
:
: Happy Ears!
: Al
:

...of course, you can mix ss and tubes at the B+ end as well.
eg. ss fw rect., large cap, damper diode tube,smaller cap.
for an easy slow starting B+
if one happens to have 6.3 and 12.6 V windings, a 19AU4GT(A),
capable of passing some 300 mA with a B+ of up to 900V,
Voltage drop ~20V, costing a mere 2 USD, fits the bill quite well ;-)

RB

[Ruud Broens]

"flipper" wrote in message
...
: On Sun, 10 Dec 2006 01:05:36 +0100, "Ruud Broens"
: wrote:
:
:
: "flipper" wrote in message
,: sn
: : I know what you mean. Call me silly, and it is. I don't know why but I
: : get all oogly googly just seeing 'em lit up. Solid state just sits
: : there, dumb and dark.
: :
: : It's *fun*. Built the little guitar amp literally from junk box parts
: : and clever whiz that I am included a line input too so it's in the
: : corner playing Beethoven's 5'th as I type. Ok, the power transformer
: : as OPT isn't going to get into Broskie's Mag but hey, it's a GUITAR
: : amp. And it glows
: :
: : Besides, the nephew thinks it's slicker than snot on glass and since I
: : built it I'm now at least on a par with Montgomery Scott, aka Scotty
: : the miracle worker, in his eyes and I didn't have to hit Warp 6.
: :
: : Hey, don't tell anybody but I crammed a MOSFET follower in there to
: : save a bottle.
: :
: :
: : Happy Ears!
: : Al
: :
:
: ..of course, you can mix ss and tubes at the B+ end as well.
: eg. ss fw rect., large cap, damper diode tube,smaller cap.
: for an easy slow starting B+
: if one happens to have 6.3 and 12.6 V windings, a 19AU4GT(A),
: capable of passing some 300 mA with a B+ of up to 900V,
: Voltage drop ~20V, costing a mere 2 USD, fits the bill quite well ;-)
:
: Yeah. I thought about doing something like that on the guitar amp
: (partly because the HV transformer is actually a bit too high) but
: I've got no filament current to spare, which is why I did the MOSFET
: follower.
:
:
: RB

sure, we've talked about that before, using what you happen to have
available is often how design specifics are arrived at :-)
(damper diodes require lotsa heating power)

specifically chosen for the purpose, i'm doing some experimenting
with the 1SH24b, the 'gridless penthode' i mentioned some time ago,
of course, functionally, there are grids, it's a penthode allright,
but physically, it is implemented as some field effect metal bars,
no grid winding whatsoever inside
extremely energy-friendly little tube, rivaling a transistor at
equivalent (lowish) voltages (50 mW or so will do).

to b cont. ..
Rudy

[Ruud Broens]

"flipper" wrote in message
...
: On Sun, 10 Dec 2006 21:48:33 +0100, "Ruud Broens"
: wrote:
:
:
: "flipper" wrote in message
: .. .
: : On Sun, 10 Dec 2006 01:05:36 +0100, "Ruud Broens"
: : wrote:
: :
: :
: : "flipper" wrote in message
: ,: sn
: : : It's *fun*. Built the little guitar amp literally from junk box parts
: : : and clever whiz that I am included a line input too so it's in the
: : : corner playing Beethoven's 5'th as I type. Ok, the power transformer
: : : as OPT isn't going to get into Broskie's Mag but hey, it's a GUITAR
: : : amp. And it glows
: : :
: : : Besides, the nephew thinks it's slicker than snot on glass and since I
: : : built it I'm now at least on a par with Montgomery Scott, aka Scotty
: : : the miracle worker, in his eyes and I didn't have to hit Warp 6.
: : :
: : : Hey, don't tell anybody but I crammed a MOSFET follower in there to
: : : save a bottle.
: :
: : ..of course, you can mix ss and tubes at the B+ end as well.
: : eg. ss fw rect., large cap, damper diode tube,smaller cap.
: : for an easy slow starting B+
: : if one happens to have 6.3 and 12.6 V windings, a 19AU4GT(A),
: : capable of passing some 300 mA with a B+ of up to 900V,
: : Voltage drop ~20V, costing a mere 2 USD, fits the bill quite well ;-)
: :
: : Yeah. I thought about doing something like that on the guitar amp
: : (partly because the HV transformer is actually a bit too high) but
: : I've got no filament current to spare, which is why I did the MOSFET
: : follower.
: :
: :
: : RB
:
: sure, we've talked about that before, using what you happen to have
: available is often how design specifics are arrived at :-)
:
: hehe. Yeah. And more than people would like to admit.
:
: The resistor dropper I came up with acts sorta like a tube rectifier.
:
: I know a resistor dropper sounds like a 'well, duh', but isn't just a
: resistor. I ran into the problem of my 100VA tranny being short on
: power when the amp was in overdrive. Seemed a bit odd to me that 100
: VA was 'not enough' but it was due to that 'too much' voltage.
:
: Anyway, if you've done the VA calculations you know the 'problem', so
: to speak, is the rectified current spikes into the filter so I added
: some transformer 'winding resistance' in the from of a series limiting
: resistor to cut those down.
:
: The power tranny as OPT is doing rather well. Certainly fine for
: guitar but not too shabby as an audio mono block either. Listening to
: Mannheim Steamroller 25'th Anniversary CD right now.
:

you know, this is one of my recurring experiences with tubes
something sounding amazingly good, considering ..
(corners were cut, it was only a first try, etc.


: (damper diodes require lotsa heating power)
:
: specifically chosen for the purpose, i'm doing some experimenting
: with the 1SH24b, the 'gridless penthode' i mentioned some time ago,
: of course, functionally, there are grids, it's a penthode allright,
: but physically, it is implemented as some field effect metal bars,
: no grid winding whatsoever inside
: extremely energy-friendly little tube, rivaling a transistor at
: equivalent (lowish) voltages (50 mW or so will do).
:
: I don't remember you mentioning that one and none of my normal sources
: seem to have a clue what it is. You got a datasheet?

err, i landed it on ABSE - it's in russian, though
hehe

: With renewed talk of SS and tubes I pulled out my current loop circuit
: again. If you remember one of the concerns was keeping the current
: balanced so I thought, shoot, why not servo it like I did the PC
: Speaker hybrid? So I've been doing some spice emulations on that.
: Works in spice, anyway
:
...and that is often encouraging enough to see what a circuit will do,
once build
yes, i remember ;-)

RB

[Eeyore]

Ruud Broens wrote:

"flipper" wrote in message
: "Ruud Broens" wrote:
:
: The power tranny as OPT is doing rather well. Certainly fine for
: guitar but not too shabby as an audio mono block either. Listening to
: Mannheim Steamroller 25'th Anniversary CD right now.
:

you know, this is one of my recurring experiences with tubes
something sounding amazingly good, considering ..
(corners were cut, it was only a first try, etc.

You know, if you're referring to using a power transformer as an output tranny, I
can only assume this must be because your expectations are so low.

Or maybe you're not that familiar with really high quality audio.

Graham

[Eeyore]

flipper wrote:

Eeyore wrote:
Ruud Broens wrote:
"flipper" wrote in message
: "Ruud Broens" wrote:
:
: The power tranny as OPT is doing rather well. Certainly fine for
: guitar but not too shabby as an audio mono block either. Listening to
: Mannheim Steamroller 25'th Anniversary CD right now.
:

you know, this is one of my recurring experiences with tubes
something sounding amazingly good, considering ..
(corners were cut, it was only a first try, etc.

You know, if you're referring to using a power transformer as an output tranny, I
can only assume this must be because your expectations are so low.

And what are your exalted expectations for a junk box guitar amp?

Or maybe you're not that familiar with really high quality audio.

Who said anything about "really high quality audio?"

That's an entirely different matter then !

Graham

[Ruud Broens]

"flipper" wrote in message
...
: On Sun, 10 Dec 2006 23:09:13 +0100, "Ruud Broens"
: wrote:
:
: "flipper" wrote in message
: .. .
: : On Sun, 10 Dec 2006 21:48:33 +0100, "Ruud Broens"
: : wrote:
: :
: : "flipper" wrote in message
: : .. .
: : : On Sun, 10 Dec 2006 01:05:36 +0100, "Ruud Broens"
: : : wrote:
: : sure, we've talked about that before, using what you happen to have
: : available is often how design specifics are arrived at :-)
: :
: : hehe. Yeah. And more than people would like to admit.
: :
: : The resistor dropper I came up with acts sorta like a tube rectifier.
: :
: : I know a resistor dropper sounds like a 'well, duh', but isn't just a
: : resistor. I ran into the problem of my 100VA tranny being short on
: : power when the amp was in overdrive. Seemed a bit odd to me that 100
: : VA was 'not enough' but it was due to that 'too much' voltage.
: :
: : Anyway, if you've done the VA calculations you know the 'problem', so
: : to speak, is the rectified current spikes into the filter so I added
: : some transformer 'winding resistance' in the from of a series limiting
: : resistor to cut those down.
: :
: : The power tranny as OPT is doing rather well. Certainly fine for
: : guitar but not too shabby as an audio mono block either. Listening to
: : Mannheim Steamroller 25'th Anniversary CD right now.
: :
:
: you know, this is one of my recurring experiences with tubes
: something sounding amazingly good, considering ..
: (corners were cut, it was only a first try, etc.
:
: Maybe tube amp 'lousy is 'lousy' in a way that's less distressful to
: the human ear than solid sate 'lousy' is
:
expectation effect, designer's ear, call it what ya like :-)
:: :
: : specifically chosen for the purpose, i'm doing some experimenting
: : with the 1SH24b, the 'gridless penthode' i mentioned some time ago,
: : of course, functionally, there are grids, it's a penthode allright,
: : but physically, it is implemented as some field effect metal bars,
: : no grid winding whatsoever inside
: : extremely energy-friendly little tube, rivaling a transistor at
: : equivalent (lowish) voltages (50 mW or so will do).
: :
: : I don't remember you mentioning that one and none of my normal sources
: : seem to have a clue what it is. You got a datasheet?
:
: err, i landed it on ABSE - it's in russian, though
: hehe
:
: Well, if they use numbers and graphs...

that's what i thought. helps to know some Russians, just in case :-)
(the first russian datasheet i encountered had no diagram of the
tube; so i soon figured ~cetka~ meant grid, but which one being which..

: Shoot me a copy if you've still got it.

done.

: : With renewed talk of SS and tubes I pulled out my current loop circuit
: : again. If you remember one of the concerns was keeping the current
: : balanced so I thought, shoot, why not servo it like I did the PC
: : Speaker hybrid? So I've been doing some spice emulations on that.
: : Works in spice, anyway
: :
: ..and that is often encouraging enough to see what a circuit will do,
: once build
: yes, i remember ;-)
:
: Don't know what to 'use' it for, yet.
:
....that's what Boole must have said about his algebra at the time..
heh
Rudy

[Patrick Turner]

flipper wrote:

On Sat, 09 Dec 2006 14:32:05 GMT, Patrick Turner
wrote:



flipper wrote:

On Sat, 09 Dec 2006 01:58:54 +0000, Eeyore
wrote:

With my interest in toobie stuff revitalised, I've had a few ideas that strike
me as rather interesting. I'll elaborate at length later.

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

The objective btw is super-linear triode stage.

Graham

Heresy! Heresy!

Or at least that's what say when I do it

Near as I can tell there are different 'levels of acceptance'. Purist
purists don't use SS.

Purists therefore prevent themselves hearing music
with as little as possible Noise & Distortions.

Sounds like what some say about using tubes at all.

Well, sure, so what?
But a tube circuit of any kind that is kept simple
can deliver both low N&D without loop FB and very high fidelity
that sounds magical.
Using techniques to increase N&D does nothing positive for the music
experience.
I like all my amps to be as linear as I think they need to be, ie, good
enough,
and usually anyone listening with the worst measuring of any gear i may
make
will have THD not more than 0.1%, and mainly 2H.
I won't proceed to supply anyone with N&D above this figure.


Nothing wrong with staying with resistance loads and tubed CCS,
and tubes only for inputs on phono amps but the price to be paid
is that the tubes cannot shine as well as thay can when not supported
by willing SS slaves working uncomplainingly and without any
measurable signal effects except reduction of N&D without using
loop FB.

But look, anything goes, really, let us not be de-facto members of the
anti novel circuit topology Gestapo.

Lighten up Pat. How in the world can you possibly imagine I'm being
some kind of 'topology Gestapo' when I list off amps I've done with SS
splattered all over the place and even gasp a hybrid?

I am already lighter, and getting lighter, and see the light more
clearly
since taking up my terrible habit of riding a bicycle for
8 of my precious hours per week.
I've lost 14Kg since July 15.

But yes, you should do whatever you takes your fancy,
and what takes it should give you better music IMHO;
That isn't an edict from the Fuhrer, just a verbalisation
if a positive intent meant.

Patrick Turner.

[[email protected]]

Eeyore wrote:
With my interest in toobie stuff revitalised, I've had a few ideas that strike
me as rather interesting. I'll elaborate at length later.

I've noticed that a number of better-performing tube stages use semiconductors
in a 'support' role such as constant current sources and maybe cascode stages
too, yet they're not actually actively amplifying the signal.

Does this acceptance extend to such things as current mirrors ?

I have a couple of things in mind that would really benefit from these but
there's no point if it's seen as being too 'impure'.

The objective btw is super-linear triode stage.

I have a personal reluctance to adding complexity to any circuit, be it
extra solid state or thermionic devices.

Solid state current sources/sinks are generally simpler than thermionic
ones and the solid state ones have a much lower minimum voltage drop.
But they can be done either way. And just putting a "long tail" via
more resistance onto a differential amp can also be done at a much much
lower part count with almost the same performance.

I enjoy working on/building/listening to tube amps largely because of
their lack of bells and whistles.

At the extreme end of bells and whistles are DVD remote controls with
over 100 buttons. Few tube amps go this level!

Historically, 60 or so years ago phono and radio manufacturers (the
moral equivalent of "hi-fi" today) started putting gobs of unnecessary
features into equipment. This escalated not so much into electronic
complexity (although there was some) but more into electromechanical
complexity (which isn't necessarily good either). The very very best of
the electricalmechanical doo-dads survived that era, the rest were
forgotten.

Tim.