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Old 4th October 2009, 04:24 AM   #1
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Default Single Ended Pentode Spud and Feedback
Usually, at least in guitar world, in a single ended pentode amp, the feedback return is to the cathode of the driver. But, in the case of a spud amp, where there is no driver, any suggestions on how to add some feedback? Any ideas?
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Old 4th October 2009, 04:47 AM   #2
ddd is offline ddd  Bulgaria
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You can ground the cathode resistor through the second coil or part of it. Add a cathode capacitor to increase the gain of the stage as well.
Mind the direction of the coil.
Last edited by ddd; 4th October 2009 at 04:55 AM.
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Old 4th October 2009, 07:04 AM   #3
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If you have just the one stage, then there's just one choice: Anode Follower.
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Old 4th October 2009, 01:07 PM   #4
Yvesm is offline Yvesm  France
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Pardon my ignorance but ... what is "spud" for ?
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Old 4th October 2009, 03:53 PM   #5
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Quote:
Originally Posted by Yvesm View Post
Pardon my ignorance but ... what is "spud" for ?
An amp with only one tube is a "one-tuber"...

A potato is a "tuber"...

Slang for potato is "spud"...

Therefore a one-tube amp or one-tuber is a spud.

makes sense, right???
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Old 4th October 2009, 06:30 PM   #6
Yvesm is offline Yvesm  France
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TNXTU
Was searching for an acronym.
I would never be able to find that by myself !

Yves.
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Old 4th October 2009, 06:53 PM   #7
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"Anode follower" is what we call inverse-feedback or Schade when talking transformer-coupled pentodes. Makes the pentode act more triode-like.

What tube?
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Old 4th October 2009, 08:47 PM   #8
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Quote:
Originally Posted by Miles Prower View Post
If you have just the one stage, then there's just one choice: Anode Follower.
I'm having trouble picturing how this will work -- am I just taking one side of the secondary and connecting it to the grid through a resistor? Or just take right from the plate ... presumably through a cap?

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What tube?
12HG7 to start with. With a 5K:32 OPT for headphone use.
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Old 4th October 2009, 08:52 PM   #9
Gordy is offline Gordy  United Kingdom
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You can ground the cathode resistor through the second coil or part of it. Add a cathode capacitor to increase the gain of the stage as well.
Mind the direction of the coil.
I think that I have seen that done, but I can not remember where.

If you have not purchased the transformer yet then you could specify one specifically for cathode winding feedback. Tim de Paravicini did that in his EAR HP4 headphone amp.
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Old 4th October 2009, 08:56 PM   #10
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If you have not purchased the transformer yet then you could specify one specifically for cathode winding feedback.
Unfortunately, I'm on a DIY diet, so the only option is to reuse what I have. The EAR seems to have its own little winding for this.
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