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Old 12th December 2012, 09:03 PM   #11
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Also Sansui AU70, A111, some Fishers, and of course McIntosh.
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Old 13th December 2012, 03:49 PM   #12
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you guys seem to know every amplifier with tertiary feedback ever made. Congratulations!
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Old 13th December 2012, 04:29 PM   #13
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Quote:
Originally Posted by Osvaldo de Banfield View Post
Are you sure you are alive or you are dreaming?
It's a PP variant of the RH topology, there is local negative voltage feedback from output tube plate to grid based on the ratio of the rp of the preceding stage and the plate to grid feedback resistor. It does lower rp in the output tube significantly depending on how much feedback is employed.
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Old 13th December 2012, 05:05 PM   #14
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Quote:
Originally Posted by kevinkr View Post
It's a PP variant of the RH topology, there is local negative voltage feedback from output tube plate to grid based on the ratio of the rp of the preceding stage and the plate to grid feedback resistor. It does lower rp in the output tube significantly depending on how much feedback is employed.
Not always what you say is true. There are 4 elementary kinds of feedback:

1) Voltage series: this is a when beta (The feedback ratio) senses voltage at output and feeds back voltage. This way input impedance is boosted, and output impedance is lowered (The most common form is a noninverting op amp with 2 feedback resistors);

2) Voltage parallel: beta senses voltage, and feedback current, input and output resistance are lowered;

3) Current series, both the output and input impedances are boosted (Triode with Rk without caps, also used in chips for vertical deflection in CRT displays);

4) Current parallel, which current in the output is sensed, and feedback as a current in the input, output impedance is boosted, and input is lowered (It makes a better current controlled current generator).

As a difference with other thread which I demonstrated my words, I will not do it here because in any textbook can be found such as demonstrations.

In some circumstances, topology of feedback can be mixed and it includes positive feedback, in the Seely´s book it is said that sometimes an amplifier can have a mix of positive current feedback and negative voltage feedback in order to obtain zero or negative output impedance.

Sorry if my English is not too good, but I believe you can understand me.

Cordially Osvaldo.
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Last edited by Osvaldo de Banfield; 13th December 2012 at 05:10 PM.
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Old 14th December 2012, 05:55 PM   #15
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Any opinion on the topic?
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Old 14th December 2012, 06:27 PM   #16
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Nah!
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Old 15th December 2012, 12:11 AM   #17
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can Ultra-Linear and a cathode feedback output transformer winding be implemented in one output stage?
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Old 15th December 2012, 03:37 AM   #18
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If you leave the screens connected as normal pentodes, arguably CFB already does this. If you want to do it "more", there's nothing wrong with that.

Tim
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Old 15th December 2012, 12:46 PM   #19
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And why lose power using ultralinear, you can use an off the shelf transformer with pentode connection and no extra windings!
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Old 15th December 2012, 01:37 PM   #20
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Quote:
Originally Posted by ruben alstad View Post
can Ultra-Linear and a cathode feedback output transformer winding be implemented in one output stage?
Yes, you will get benefits of both, actually I did it in 2 push-pull amps.
For details you can look for a book written by Menno van der Veen (I recommend last edition).
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