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6EM7 Floating Paraphase (I know humor me please)
6EM7 Floating Paraphase (I know humor me please)
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Old 8th February 2018, 07:38 PM   #21
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by Kay Pirinha View Post
This resistor, in line with the voltage divider between both anodes, appears to be essential with the original Floating Paraphase idea. Their value shold be much smaller w.r.t. the following stage's grid leak resistors, though.
Best regards!
There is nothing "floating", you need a very very high gain for that.Here the "floating" point carry a voltage (AC) used by the tube to produce the same voltage of the first tube, but 180 out of phase.
The R9 loads the circuit that provide the grid AC, effectively making the inverting stage gain smaller.
Mona
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Old 8th February 2018, 08:04 PM   #22
AmadeusMozart is offline AmadeusMozart  New Zealand
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No, it is the shared cathode. A true floating paraphase inverter can have two totally different tubes which cannot be the case if you have a shared cathode. Be aware that a cathode that is not bypassed has negative feedback, the 12AX7 drops from approx 40x amplification to approx 14.2x according to my calculation. The drawback is that when you do not bypass the cathode-heater leakage can give hum so you have to use a tube with little leakage. On another note: the 6SN7 is about the most linear double triode that you can find, I like that tube a lot.

edit: I do not like fixed bias. That is fine if you want maximum power output but you run the risk of shortened tube life and higher distortion, especially if the tubes are not well balanced. I cannot find the article anymore (but am certain about it since I queried the Audio Note setup) but for the least distortion Mullard recommended to bias the output PP a bit more towards class B than the normal AB recommended and to use individual cathode resistors.

Forgot to mention that you will loose the ability to adjust the balance which means that you cannot adjust for minimum distortion at the output.
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Old 9th February 2018, 07:01 AM   #23
AmadeusMozart is offline AmadeusMozart  New Zealand
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Paraphase Splitter Experiments
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Old 9th February 2018, 08:33 AM   #24
Ketje is offline Ketje  Belgium
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Originally Posted by AmadeusMozart View Post
That's no good.They put an attenuator before the phase inverter to compensate for it's gain.But the gain is not a constant, bad compensation.
Mona
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Old 9th February 2018, 09:28 AM   #25
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by Ketje View Post
There is nothing "floating", you need a very very high gain for that.Here the "floating" point carry a voltage (AC) used by the tube to produce the same voltage of the first tube, but 180 out of phase.
The R9 loads the circuit that provide the grid AC, effectively making the inverting stage gain smaller.
Mona

Erm, what did Norman Crowhurst tell us in his papers shown in #6, especially in pics 1 and 2?
Best regards!
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Old 9th February 2018, 12:04 PM   #26
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by Kay Pirinha View Post
Erm, what did Norman Crowhurst tell us in his papers shown in #6, especially in pics 1 and 2?
Best regards!
Well, he agrees with what i said, it becomes floating with very high gain of the inverting stage.But with tubes, ~70x with ECC83, we are far away from very high.The resistor grid-ground makes a difference, see my calculation.
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Old 10th February 2018, 05:15 AM   #27
PRR is offline PRR  United States
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Originally Posted by mashaffer View Post
..t. What is the reason for different bias points for the two halves of the AX7?
What difference?

The added 200r in one cathode? Big deal.

Also note that there is 3.3K to ground (through OT) on the high end of that 200r. It may not be so very different after all. However I'm sure another 200r is not going to "mis-bias" the triode-- a wide range will work.
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Old 10th February 2018, 09:03 AM   #28
Ketje is offline Ketje  Belgium
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Originally Posted by mashaffer View Post
Thank you for joining in. Interesting circuit. What is the reason for different bias points for the two halves of the AX7?
If you don't like that, a simple solution...
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Old 10th February 2018, 02:33 PM   #29
mashaffer is offline mashaffer  United States
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Oh, I see it now. It wasn't that I didn't like it I just wondered why it was there. What I missed is that it is a part of the GNF loop and not in there for the purpose of bias. makes perfect sense I just failed to think globally.
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