Another simple way would be OldEurope's Triodlington,
if you can locate an NPN with a consistant flat beta of 2.
That would be a really easy circuit to fudge.
-------------------------------------------------------------------
Anyways, aside from the cheap cheap, why cheat at all?
Why not just use parallel 300B's? I'll give you one good
reason that rarely comes the fore: Constancy of Mu.
Take a great audio triode like the 300B, the construction
is very flat and parallel. And the resulting curve set is also
very upright and parallel. Resists leaning over to the right
with increasing voltage.
Take an ordinary coaxial triode, and the curves often lean
something fierce. Why? Because its not one uniform triode,
but a blended set of many parallel triodes, that are not all
exactly equal. Not all cut off with the same sharpness.
Smoking Amp proposed the theory, but I had to prove this
to myself. Averaging several sets of dissimilar but perfect
triode curves, did result in the more common leaning set.
So, if you blend two real 300B's that are not quite twins,
the resulting blended curve may lose some benefits of the
flat internal construction. Now its its like one bigger 300B
with sloppier construction.
Mirrored or Anti-mirrored clones have no such issues.
As forced perfect copies, their internal construction is
almost irrelevant. They cannot degrade the curvature
of the original in the averaging process.
if you can locate an NPN with a consistant flat beta of 2.
That would be a really easy circuit to fudge.
-------------------------------------------------------------------
Anyways, aside from the cheap cheap, why cheat at all?
Why not just use parallel 300B's? I'll give you one good
reason that rarely comes the fore: Constancy of Mu.
Take a great audio triode like the 300B, the construction
is very flat and parallel. And the resulting curve set is also
very upright and parallel. Resists leaning over to the right
with increasing voltage.
Take an ordinary coaxial triode, and the curves often lean
something fierce. Why? Because its not one uniform triode,
but a blended set of many parallel triodes, that are not all
exactly equal. Not all cut off with the same sharpness.
Smoking Amp proposed the theory, but I had to prove this
to myself. Averaging several sets of dissimilar but perfect
triode curves, did result in the more common leaning set.
So, if you blend two real 300B's that are not quite twins,
the resulting blended curve may lose some benefits of the
flat internal construction. Now its its like one bigger 300B
with sloppier construction.
Mirrored or Anti-mirrored clones have no such issues.
As forced perfect copies, their internal construction is
almost irrelevant. They cannot degrade the curvature
of the original in the averaging process.
Assuming your question is in regard to cathode coupled
anti-triode, and not the paraphase driven version...
Virtually grounded cathode. Why would that be any more
difficult for the reference triode? One half of the load is on
the real plate, the other half on the Anti-plate.
Don't you see? By strongly holding the tail voltage at
virtual ground, the Anti-triode is forced to add or steal
exactly the opposite current as the real cathode. And
thats where the magic happens.
------------------------------------------------------
Now having said that, I might point out that all cathode
coupled anti-triodes are gonna have trouble knowing an
A2 grid current should not result in an Anti-plate current.
I don't think the paraphase version is so affected.
-------------------------------------------------------
Also a Triodlington might misinterpret an A2 grid current
as something its beta should multiply, which wouldn't be
an accurate cloning if driven hard....
But if you connect a PNP Base to the Plate, Collector
to Cathode, and Emitter to Load, as a Baxendall pair.
I think then you multiply pure plate current only.
And the Triode still regulates the Base in a "4th circuit"
mode to keep the Bipolar from running away (if it tries,
it starves the triode, which shuts off the base), just as
Triodlington stabilizes an NPN.
You could take something small, with the same sort
of internal construction, like a 45, and make a really
huge fake 300B out of it.
Of course this solution is entirely single ended current
multiplication, and requires a SE OPT.
----------------------------------------------------------
Note the ---'s above. Don't be confused, I'm talking
about three entirely different methods to skin a cat.
anti-triode, and not the paraphase driven version...
Virtually grounded cathode. Why would that be any more
difficult for the reference triode? One half of the load is on
the real plate, the other half on the Anti-plate.
Don't you see? By strongly holding the tail voltage at
virtual ground, the Anti-triode is forced to add or steal
exactly the opposite current as the real cathode. And
thats where the magic happens.
------------------------------------------------------
Now having said that, I might point out that all cathode
coupled anti-triodes are gonna have trouble knowing an
A2 grid current should not result in an Anti-plate current.
I don't think the paraphase version is so affected.
-------------------------------------------------------
Also a Triodlington might misinterpret an A2 grid current
as something its beta should multiply, which wouldn't be
an accurate cloning if driven hard....
But if you connect a PNP Base to the Plate, Collector
to Cathode, and Emitter to Load, as a Baxendall pair.
I think then you multiply pure plate current only.
And the Triode still regulates the Base in a "4th circuit"
mode to keep the Bipolar from running away (if it tries,
it starves the triode, which shuts off the base), just as
Triodlington stabilizes an NPN.
You could take something small, with the same sort
of internal construction, like a 45, and make a really
huge fake 300B out of it.
Of course this solution is entirely single ended current
multiplication, and requires a SE OPT.
----------------------------------------------------------
Note the ---'s above. Don't be confused, I'm talking
about three entirely different methods to skin a cat.
Most power transformers have only one 70 volt tap. This means the usual rectifier is a half wave resulting in 60 (or 50) Hz ripple. The center tap will be grounded so a full wave doubler is not possible either. The mosfet followers will draw 5 to 10 mA each off of the negative supply. You might have trouble getting a clean negative supply from a half wave rectifier at currents of 20 to 40 mA. If you try this, an active filter or regulator using a mosfet might be a good idea.
The new Antek toroid has two 70 volt taps. I bought one, but haven't hooked it up yet. I plan to use it to feed the negative supply for a PowerDrive circuit in a big push pull amp.
Forgot George had already done exactly that.
Baxendall thing with a 45, I mean to say...
http://www.tubelab.com/SuperTubeSE.htm
Baxendall thing with a 45, I mean to say...
http://www.tubelab.com/SuperTubeSE.htm
They are all just "Darlington things" to me. Since that time I have done some more of these "darlington" experiments.
I hacked up a Simple SE board and put an NPN transistor where the cathode resistor should be. It worked. Next a mosfet, worked better. The tube was a 6Y6 because it works well on 150 volts. I remember posting some of these experiments, but could not find the thread. My old Fluke power supply was the limiting factor. I now have a BIG power supply, so this will be revisited.
There were some hybrid experiments when I was playing with push pull amps too. Power supply problems again limited the fun but big power and big fat sound was flowing from a surplus power toroid. More of this when the driver board is done.
Pentode boosted by a bipolar may act very Darlington-ish-y...
The same can not be said of a Triode boosted by a bipolar.
Though both circuits look similar at first glance, I can't lump
Triodlingtons with Darlingtons when they work so different.
The reason they are different, is that the Triode "sees" the
collector to emitter voltage (minus an emitter drop) as yet
another input to the amplification equation. True Darlington
would totally ignore (aside from the Early effect).
It lends intrinsic space charge feedback to control the base
of the Transistor. The very same internal Schading (or Mu)
that makes a Triode linear with Voltage, now acts upon
the Transistor as well! Rather than blindly acting upon Gm
and/or Beta without regard to the resulting Voltage.
It completely stabilises the transistor against runaway
without the need for additional resistance in the emitter.
And the resulting collector impedance is lowered, rather
than raised.
Same same for the PNP Sizzler. I love the Malibu Chicken.
The same can not be said of a Triode boosted by a bipolar.
Though both circuits look similar at first glance, I can't lump
Triodlingtons with Darlingtons when they work so different.
The reason they are different, is that the Triode "sees" the
collector to emitter voltage (minus an emitter drop) as yet
another input to the amplification equation. True Darlington
would totally ignore (aside from the Early effect).
It lends intrinsic space charge feedback to control the base
of the Transistor. The very same internal Schading (or Mu)
that makes a Triode linear with Voltage, now acts upon
the Transistor as well! Rather than blindly acting upon Gm
and/or Beta without regard to the resulting Voltage.
It completely stabilises the transistor against runaway
without the need for additional resistance in the emitter.
And the resulting collector impedance is lowered, rather
than raised.
Same same for the PNP Sizzler. I love the Malibu Chicken.
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