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dsavitsk 4th October 2009 05:24 AM

Single Ended Pentode Spud and Feedback
 
1 Attachment(s)
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?

ddd 4th October 2009 05:47 AM

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.

Miles Prower 4th October 2009 08:04 AM

If you have just the one stage, then there's just one choice: Anode Follower.

Yvesm 4th October 2009 02:07 PM

Pardon my ignorance but ... what is "spud" for ?

Michael Koster 4th October 2009 04:53 PM

Quote:

Originally Posted by Yvesm (Post 1941566)
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???

Yvesm 4th October 2009 07:30 PM

TNXTU
Was searching for an acronym.
I would never be able to find that by myself !

Yves.

revintage 4th October 2009 07:53 PM

"Anode follower" is what we call inverse-feedback or Schade when talking transformer-coupled pentodes. Makes the pentode act more triode-like.

What tube?

dsavitsk 4th October 2009 09:47 PM

Quote:

Originally Posted by Miles Prower (Post 1941387)
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?

Quote:

Originally Posted by revintage (Post 1941783)
What tube?

12HG7 to start with. With a 5K:32 OPT for headphone use.

Gordy 4th October 2009 09:52 PM

Quote:

Originally Posted by ddd (Post 1941345)
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.

dsavitsk 4th October 2009 09:56 PM

Quote:

Originally Posted by Gordy (Post 1941849)
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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