Cathode Follower "ends"

[Guitarist]

Does the plate resistor and the following cathode resistor have to match? eg. 100k & 100k (12ax7) or 33K and 33K (12au7). A comment to this effect has me thinking.

I've got an amp the sounds weak/treble clippy in this circuit area and thought this may be why. I'm about to Valve Wizards (see bottom figure): The Valve Wizard

thank you.

[loudthud]

IIRC examples of different resistors are Vox AC100 and Ampeg SVT (12DW7). The problem usually seen when you use a 12AX7 is not allowing enough B+ for the cathode follower. The cathode follower will clip the positive side when it has about 100V plate to cathode voltage. So if B+ is 300V and the plate voltage of the gain tube is 200V, you have virtually no headroom on positive peaks. Bias the gain triode for a plate voltage of 150V or so. Use a cathode bias resistor of 820 instead of 1.5K.

[tubeswell]

Depends on the bias that you want for the CF stage and any particular DC coupled stage drving it and how much non-linear wave form you want coming out of the CF (remembering that in a direct DC coupled pair the Cf stage 'steals' tube current from the inverting stage). The inverting stage's plate resistor and the CF stage's cathode resistor don't have to be the same.

[Guitarist]

Call me crazy but I've been loving the distortion made by 12au7/12ay7 tubes or similarly a 12dw7/832 punishing the next. So I've been trying to steer things away from the 100K/x7 zone and into 33K-47K 12ay7/u7 range. Plate voltage is usually high, say 250V, and I think preamp tubes should be biased hot for tone—just like output tubes. So move the cathode bias resistor down lower say 470Ω 1 watt or less? So if we want current then open up the bias, right?

Edit: attached a sample schematic.
If the 12au7 can take more on the grids then it might be more resistant to blocking distortion too, so the usual 470Ks could be reduced? This is looking like a redesign of the Marshall V2.

[DumbGuitarPlayer]

, and I think preamp tubes should be biased hot for tone—just like output tubes.

This caused me to leave this thread.

[Steve Conner]

Well, if you left, who just posted that?