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Old 21st November 2010, 08:01 PM   #1
Jaap is offline Jaap  Netherlands
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Default RH807 push pull ?

You could double the RH807 and add a input transformer as splitter.
Would this be a good idea ?
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Old 22nd November 2010, 08:37 AM   #2
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To make a push-pull amplifier requires different type of output transformer.
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Old 22nd November 2010, 04:47 PM   #3
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Quote:
Originally Posted by artosalo View Post
To make a push-pull amplifier requires different type of output transformer.
I am aware of that. But I wonder if people have tried it, a simple two stage 807PP with local feedback and inputtransformer as a splitter, and what operating point they chose.
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Old 22nd November 2010, 05:26 PM   #4
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You can find your operating point in this detailed 807 datasheet: http://www.retrovox.com.au/STC807.pdf

I think it will work fine.
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Old 22nd November 2010, 06:02 PM   #5
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Here is an amp that intrigued me. Outputs are 807 precursors, Amp itself is a precursor to the Allen Wright PP1c. The cascoded LTP at the front is ideal for RH style feedback.

dave
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Old 22nd November 2010, 06:59 PM   #6
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To be honest I was thinking about using this front-end (designed by JC Morrison) for a 807PP amp with local feedback.
See also: new amp design @ Lab JC
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Old 22nd November 2010, 07:24 PM   #7
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That has one more stage than is needed i think.

dave
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Old 22nd November 2010, 09:00 PM   #8
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The RH807 design depends on plate feedback current influencing the plate voltage of a relatively high Rp triode. Feedback would need to go to the 1st stage before the cathode follower. With the RH807 a CCS is not used on the driver plate, but certainly could be.

The cathode follower is not needed to drive an 807 unless you want A2 operation.

The cascode is cool but that driver balance pot is weird. It would need a little rework for local feedback.

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Old 22nd November 2010, 10:10 PM   #9
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Quote:
Originally Posted by planet10 View Post
Here is an amp that intrigued me. Outputs are 807 precursors, Amp itself is a precursor to the Allen Wright PP1c. The cascoded LTP at the front is ideal for RH style feedback.

dave
Cascoded LTP in front of 6L6 derivatives with Schade style LFB is Miles' signature dish isn't it?
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Old 23rd November 2010, 09:39 AM   #10
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To be honest, I'm working on an 807pp amp myself.
60W AB2
That is, 400V on the anodes of 807, 300V (regulated) on the screens.
It uses fixed bias.
Front end is EF184 in a LTP. 350V B+ (regulated) and 175V (regulated) on screen.
Plate resistors are 27k. After the EF184's come the coupling capacitors that are connected to the source followers that connect directly to the 807's.
Some days ago, I connected the anodes of the 807's through a 220k resistor to the plates of the EF184's. It works fine! I didnt like the sound with smaller resistors, it was too 'sterile'.
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