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Old 26th August 2003, 02:16 AM   #11
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Quote:
Originally posted by fdegrove
Those few, and you can count me in, are actually in the good company of RCA who actually described what was going on in their manuals.
I much prefer the output pair to be well balanced, and a CCS in the tail is excellent. If you want some imbalance, and I'm not entirely convinced by what I've heard so far, then do it in the gain/driver stage.

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I have the article somewhere in my archives...
I'd like to read that....
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Old 26th August 2003, 02:45 AM   #12
SY is offline SY  United States
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Brett: Most driver/gain stages have some degree of imbalance to begin with. You can polish a turd by introducing a complementary imbalance in the output stage.

I suspect that we'd agree that it's best to make the whole shmeer well-balanced to begin with so that we don't have to do unstable tricks like that in the first place.
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Old 26th August 2003, 02:52 AM   #13
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Quote:
Originally posted by SY
polish a turd
Mods can say that!?

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Old 26th August 2003, 02:53 AM   #14
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Hi,

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I'd like to read that....
And you will...

WHEN A SEE SAW IS JUST THAT...

Cheers,
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Old 26th August 2003, 03:04 AM   #15
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Hi,

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I suspect that we'd agree that it's best to make the whole shmeer well-balanced to begin with so that we don't have to do unstable tricks like that in the first place.
Ever specced a xformer and measured what you actually paid for?

Ever wondered why those tubes that measured so well on the the tester didn't match so well in the amp?

Shall I go on? Or shall we open up a book and dig into AC current flow?

Maybe I should publish one of those rags too?

Come on you guys, use those little greys cells for a change.

Cheers,
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Old 26th August 2003, 06:02 AM   #16
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Quote:
Originally posted by SY
Brett: Most driver/gain stages have some degree of imbalance to begin with. You can polish a turd by introducing a complementary imbalance in the output stage.

I suspect that we'd agree that it's best to make the whole shmeer well-balanced to begin with so that we don't have to do unstable tricks like that in the first place.
My preference is to have it balanced well all the way, usually with CCS's in the tails. However, fiddling with a paraphase splitter has been interesting. At about 5% imbalance it seems to fatten up a little bit (more robust sounding) with no real negative sonic consequences, so far. I'm still in the courtship stage with this topology so after the flush or harmonic hormones has worn off, I may find myself having an epiphany, finally understanding why the Scots call them lassies, and saying a quick farewell.
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Old 26th August 2003, 12:11 PM   #17
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Congrats, Brett, you've discovered the secret of SET magic! And with open eyes yet, which puts you one up on most people.

Frank, yes, I've done one or three of those measurements. The real issue I've seen in balance at the low and mid frequencies versus the balance at high frequencies. The latter can be brought into line, if need be, by some compensation capacitance. Or, if you've got a triode class A stage, by neutralizing caps.
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Old 26th August 2003, 09:49 PM   #18
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Originally posted by SY
Congrats, Brett, you've discovered the secret of SET magic! And with open eyes yet, which puts you one up on most people.
LOL. I don't think that's all the SE 'magic'; there's an o/p Z that modulates with the signal waveform, low inductance OPT's and often really poor PS design too.

The EL84 amp I mentioned above is nice, but isn't a patch on the PP amp I use as my main unit. I was just surprised (again) at the effect it had. The amps going into the bedroom system so it will be fine driving a crappy Tannoy Red.
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Old 27th August 2003, 03:53 PM   #19
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Default back to bias

Firstly: thank you analog_sa for the Beard circuit.

OK, so CCS's are a possible bias solution. Now has anybody considered differentially driving an output tube as follows (sorry, can't supply drawing right now...)

P-channel FET in cathode circuit, using a small separate CCS to fix Vgs and therefore Is. Drive gate and tube grid equally, in anti-phase from a LTP...

I'd like to hear the tube guru's input on this (no pun intended)...
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Old 27th August 2003, 04:22 PM   #20
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Quote:
Originally posted by fdegrove
Ever specced a xformer and measured what you actually paid for?
But did you ask for perfect balance? It's not actually a problem to make transformers that have (near as dammit) perfect balance, and that's why broadcasters use them for microphone and line-level signals in noisy television studios. Exactly the same techniques can be used in an output transformer, but if you don't ask, you don't get.
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