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Hoffman Amps Forum image Author Topic: Valve Wizard cathode follower diode/resistor question  (Read 670 times)

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Offline jordane

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Valve Wizard cathode follower diode/resistor question
« on: June 15, 2025, 10:42:53 am »
I have built a Plexi SE that sounds good as is, but my question is about the VW (edit: Valve Wizard) cathode follower tweaks, from here:
https://www.valvewizard.co.uk/dccf.html

Merlin shows two versions of a resistor-diode in series between the grid of the second triode in the cathode follower (V2b, not noted on my schematic but I modified the design in my build) and cathode of V2b. Forgive me if this has been discussed, I can’t find much through searching.

The first schematic shows a 10k into the diode, and the second shows a 47k into the diode. I’m wondering whether there’s a functional difference between the two. The one I built uses the 10k->diode… but possibly the 47k->diode would suit me better?

Schematics included.
« Last Edit: June 15, 2025, 11:28:21 am by jordane »

Offline Willabe

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Re: Valve Wizard cathode follower diode/resistor question
« Reply #1 on: June 15, 2025, 11:24:10 am »
...... the VW cathode follower tweaks

There's a reason we use words, not just a letter for a word.

What is 'VW' mean?

If you would at least spell out the words the 1st time, then you can use letters further on. 

Offline jordane

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Re: Valve Wizard cathode follower diode/resistor question
« Reply #2 on: June 15, 2025, 11:27:52 am »
Apologies, will edit the first post. VW=Valve Wizard.

Offline Merlin

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Re: Valve Wizard cathode follower diode/resistor question
« Reply #3 on: June 15, 2025, 11:30:01 am »
I was over-cautious when I started using that mod, I didn't want the diode to overwrite the tube clipping, so I used a generous 47k resistor. Later I dropped down to 10k as that also seemed fine. Finally, I'm now satisfied the resistor isn't necessary at all, the tube will draw plenty of grid current well before the diode conducts (I need to update the webpage, ahem).
« Last Edit: June 15, 2025, 11:32:38 am by Merlin »

Offline jordane

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Re: Valve Wizard cathode follower diode/resistor question
« Reply #4 on: June 15, 2025, 11:58:44 am »
Merlin, thank you for providing your input. I have read your website pages many times! I need to order a copy of your book.

I really appreciate your writing.

 


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