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Old 25th November 2010, 04:37 AM   #11
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Quote:
Originally Posted by Wavebourn View Post
You may use couple of resistors instead of transistor. The same dynamic load, the same positive feedback from cathode follower, but without additional transistor with it's non-linearities.
The transistor would be at constant current too. Only Early to worry about.
You mean bootstrap two 22K resistors in the middle with yet another cap???
I don't see that RC delay being better linear then the worst direct coupled
transistor on earth. OK I exaggerate, its better than 2N3055, but not much.
And then we back to needing bootstrap caps of supreme quality.

Oh wait, maybe you mean resistor direct from V2 cathode! Yeah, I see it now.
Whats 1.8mA stolen away from 70mA? We don't need no stinkin' tranzeestor.

V2's cathode is 16V higher than V1's plate, and they don't have to operate
at the same current. The remaining 68ma dumps through R4.

Last edited by kenpeter; 25th November 2010 at 04:47 AM.
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Old 25th November 2010, 05:04 AM   #12
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Freakin' genius! I hope someone pays that man's salary.

Got a few of them FDA banned Four Loko in the trunk.
Need to bust out and celebrate, if taste don't gag me.
Man, I hear that stuff is nasty.

I don't appear to be sleeping tonight anyway...

-----

Nevermind the 6AS7 curve set. Its clear in Diego's
very first schematic that V2's cathode is 23V higher
than V1's plate. Assuming real live measurements?
25K still good for POT2, even closer to the middle.
We need 12K7 thereabouts.
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Last edited by kenpeter; 25th November 2010 at 05:29 AM.
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Old 25th November 2010, 06:34 AM   #13
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Quote:
Originally Posted by kenpeter View Post
I hope someone pays that man's salary.
Nobody can afford a genius, so all geniuses are jobless...


Here you go:
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Old 25th November 2010, 06:52 AM   #14
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Please disregard value of R3: Rimu Schematics puts default 1K value.
Couple of resistors may be added: one in anode of 1'st triode to B+, and another to cathode of the right bottom triode, to better fit some particular tubes and their curves, but it's not necessary...

Happy Thanksgiving!
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Old 25th November 2010, 08:14 AM   #15
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One more version:
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Old 25th November 2010, 03:06 PM   #16
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R1 has constant current drawn across constant voltage drop.
Same constant current then through R2 and/or grid(s) of V3.
Suggesting V3 dumbed down to single triode plate resistance in
case #1, or something slightly closer to a current source in
case #2 (cascode of three triodes with constant grid voltage).

Why isn't V3 an active player here? Am I missing something?
Is CCS supposed to be better than 1K resistor? Cathode of V2
will still see current variations into 300ohm headphone load.

Drive V3 from error sense resistor above plate of V2, as a
White Cathode Follower, now maybe you got something...
V3 would then hold V2 at constant current by dumping the
dynamic opposite of the headphone load.

Last edited by kenpeter; 25th November 2010 at 03:27 PM.
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Old 25th November 2010, 05:37 PM   #17
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Direct coupled method for top triode to also operate at constant current.
Hopefully, PNP current dumping could dispose of observed load variations?

Note: Even if we set currents equal, voltage drops won't necessarily be.
Voltage on V1a is set by Mu, and the remainder still has to add up to B+.
Wanna tweak for equal voltages? Result: slightly higher bias than 1.8ma,
but I don't see any reason that would be a problem.

MJE350 might be a poor choice, would have to cherry pick a good one.
Darlington like TIP147 does not offer the voltage we need. Or mix your
own pair of PNP discretes. Base current could be high as 2.3mA if you
randomly grab MJE350 of the minimum spec, min useless for 1.8mA CCS.

The good news, it will be dissipating 6 or 7 Watts, so HFE will have the
benefit of toasty warmth. Heatsink required. No worry, rated for 20W.

I've thrown two new resistors at the problem of current measurements.
R4 updated to 600 to maintain 70mA, necessitated by top triode change.
I might have made a mistake, R4 might still need to be 1K, not certain...

Might be technically better than the previous one? But I kinda prefer
simplicity over obsessive constant current everywhereness...
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Last edited by kenpeter; 25th November 2010 at 05:54 PM.
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Old 25th November 2010, 05:51 PM   #18
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Quote:
Originally Posted by kenpeter View Post
R1 has constant current drawn across constant voltage drop.
Not exactly. Triode is not ideal, and loaded on not ideal constant current source. This not ideal error is amplified by right bottom triode supplying some error correction. Right handed triode has high output resistance, so it looks more like modulated current source decreasing variations of current through cathode follower.
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Old 25th November 2010, 06:02 PM   #19
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The detected error at R2 has shrunk by 1/(Mu-1), V3 will need a lot of gm to fix anything!
Make V3 MOSFET or BJT, and you have Triodlington, and a situation where the current
variance of error in V1 is dumped by sand, leaving even more constant current in Triode
V1, which is the loadline with our best hope for Mu...

Last edited by kenpeter; 25th November 2010 at 06:16 PM.
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Old 25th November 2010, 06:19 PM   #20
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Quote:
Originally Posted by kenpeter View Post
The detected error at R2 has shrunk by 1/(Mu-1), V3 will need a lot of gm to fix anything!
Make V3 MOSFET or BJT, and you have Triodlington, and a situation where the current
variance of error in V1 is dumped by sand, leaving even more constant current in Triode
V1, which is the loadline with our best hope for Mu...
Right handed triode has high mu. And sand current mirror can be used also.
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