https://m.imgur.com/a/1bBy8
I followed this schematic (the black line version) almost to the letter (a few minor changes are annotated on the drawing) and it worked really good. Sounded great, loud, everything worked.
The 6F4P is a Pentode-triode. It's similar to ECL84, (and ECL86, ECL82...) I had one unused triode and I wanted to try a cathode follower so I made the following changes. First I changed the ceramic comp 47k input resistor to a wire-wound 39k in an effort to reduce noise. The resistance was changed only because it's the only wire-wound I had on hand. Then I got rid of the coupling capacitor and wired in the cathode follower as shown.
Result - as I turn the volume knob from 0 to 10 I hear some quiet fuzzy sounds at 1, dead silent from 1 to 9, then more fuzz and then at max volume you can hear the guitar and it actually sounds really good, but its very quiet. It's definitely below conversation level.
So I did something wrong, but I was wondering if anyone sees any obvious mistakes first.
I followed this schematic (the black line version) almost to the letter (a few minor changes are annotated on the drawing) and it worked really good. Sounded great, loud, everything worked.
The 6F4P is a Pentode-triode. It's similar to ECL84, (and ECL86, ECL82...) I had one unused triode and I wanted to try a cathode follower so I made the following changes. First I changed the ceramic comp 47k input resistor to a wire-wound 39k in an effort to reduce noise. The resistance was changed only because it's the only wire-wound I had on hand. Then I got rid of the coupling capacitor and wired in the cathode follower as shown.
Result - as I turn the volume knob from 0 to 10 I hear some quiet fuzzy sounds at 1, dead silent from 1 to 9, then more fuzz and then at max volume you can hear the guitar and it actually sounds really good, but its very quiet. It's definitely below conversation level.
So I did something wrong, but I was wondering if anyone sees any obvious mistakes first.
I believe I am. The reference I used didn't show a coupling cap - seemed strange but I don't honestly know any better. So is that the thing?
I guess the reference drawing was wrong.
Yes, You need to add a capacitor between the cathode of the follower and the volume pot to keep the DC off the pot, and out of the grid of the next tube. The bias is changing when you turn the pot, and is always positive!
Lol. I convinced myself to delete it because it's called a "DC Coupled" cathode follower. Outsmarted myself.
It's at least one thing for sure, so add the coupling capacitor back.
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Ah okay. Thank you for that.
I had the circuit working again just now. It didnt take long to put the one coupling cap back in. It worked and sounded like a real amp again except that it still seemed quiet. Dimed - I'd say that it might've had about as much volume as a cheap set of PC speakers. It was definitely louder when I originally put it together.
I suppose that the elements that you pointed out are the likely culprits..
This is basically my third circuit so I'm still fumbling around. Now that you point it out to me though - I guess there ought to be some kind of a ground reference on the grid of the second valve. Is that the right name for what I need to add?
Yes, the grid needs some voltage reference point. In this case the volume control itself does that.
Sorry, I misread the circuit at first, now it should work. If not, there's some other problem.
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