Today on the Breadboard: The Power Face

[Chuck D. Bones]

Who says you can't make a Fuzz Face with tubes? If you build this, watch out for the high voltage. I'm still tweaking component values. Total current draw is around 12mA.

 

[KR Sound]

Awesome. You have this on the board already?

 

[Chuck D. Bones]

Still in the simulation stage.

 

[swyse]

That's awesome. What is WW on VR1? I don't know enough about tube circuits to know if this is an april fools day prank but this looks super interesting.

 

[Chuck D. Bones]

Wirewound. Turns out it doesn't need to be. Pot needs to be rated for 1/2W or higher. C-taper is better.

 

[Bricksnbeatles]

That's awesome. What is WW on VR1? I don't know enough about tube circuits to know if this is an april fools day prank but this looks super interesting.

presumably a designator for “wire wound”— a sure wound pot

 

[steviejr92]

Well i already have an EF86....

 

[Chuck D. Bones]

Schematic updated.

 

[steviejr92]

What was changed? If I may ask.

 

[Chuck D. Bones]

R5, R7 & C5 were changed. R8 & the notes were added.

I lowered V2's plate current. Added R8 because we probably don't need 150Vp-p output. That would destroy most pedals and transistor amps.

One could replace R5 with an output transformer and drive a speaker for a little over 1W output.

 

[steviejr92]

At 1W that would make the perfect little bedroom amp! And a gnarly one at that! I’m pretty interested on what this would sound like.

 

[Chuck D. Bones]

OK, I have a confession. I initially posted this as an April Fools prank. On reflection, it could be made to work either as a dirt pedal, headphones amp or practice amp. If all we want is a pedal, then we don't need a power pentode for V2. Instead, we could lower the B+ and use a small signal pentode like another EF86 or a 6AK5. If what we're after is a headphones or practice amp, then we just replace R5 with an output transformer and put a VOLUME control up front. The FUZZ pot can be a fixed resistor that gives us the desired maximum gain.

 

[Chuck D. Bones]

BTW, here's a vintage guitar amp circuit that bears a strong resemblance to the schematic I presented above. I was not looking at or thinking about this circuit when I drew the one above. RV1 is VOLUME, RV2 is TONE (treble cut) and RV11 is a kind of BASS BOOST. Some of the resistor values are suspicious, like R3, R5 & R7 for instance. Maybe they're correct.