Here is my modest attempt at designing a linestage with the 12B4A tube. I think it will give good performance. The Rp is so low that there shouldn't be too much distortion at the output. The gain of this circuit is low ( 4? 5? ) but I don't need much if any. I decided on a anode follower because evidently CF don't have very good PSRR. So I think I will give this a shot a see how it sounds. I'll let you know.
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Hey-Hey!!!,
I will have to say that the 12B4 is a good linestage tube. I personally like the 12SN7 better, but that is not important at this time. In the experimenting I did with the 12B4, I found that 180-200 volts on the plate sounded best at 10 mA of current. LED biased to near 30 volts at the cathode( 14 red ones, one yellow). I never tried this one with a resistive load, and went straight to cascoded mosfets.
I also use the 12B4 as a driver stage in the PP amps, choke loaded and common cathode, diff-pair rigging( CT choke ). The tube exhibits less increase in plate resistance as voltage increases than most( actually, any that are comparable in performance )., and can stand 5-600 volts on its plate without worry. And the open anode structure lets those big cathodes glow for all to see. Toooo cool!!!
regards,
Douglas
I will have to say that the 12B4 is a good linestage tube. I personally like the 12SN7 better, but that is not important at this time. In the experimenting I did with the 12B4, I found that 180-200 volts on the plate sounded best at 10 mA of current. LED biased to near 30 volts at the cathode( 14 red ones, one yellow). I never tried this one with a resistive load, and went straight to cascoded mosfets.
I also use the 12B4 as a driver stage in the PP amps, choke loaded and common cathode, diff-pair rigging( CT choke ). The tube exhibits less increase in plate resistance as voltage increases than most( actually, any that are comparable in performance )., and can stand 5-600 volts on its plate without worry. And the open anode structure lets those big cathodes glow for all to see. Toooo cool!!!
regards,
Douglas
Not too bad at all. But contrary to Douglas' opinion, I fond the 12B4A in a linestage runs better with about 100Va-k and about 25 - 35mA. So my suggestion would be to adjust the bias resistor down to about 440R (vg = -11V) and adjust the dropper in the PSU to get it to 310V again. Gain will be around 5 and the output Z ~ 900R
Better still would be to ditch the last RC in the PS and up the value of the anode R to about 10k keeping the current around 25mA. You'll need a 25W resistor for that; 2 x 5k 12W Mills in series or 2 x 20k in // would be fine.
Better still would be to ditch the last RC in the PS and up the value of the anode R to about 10k keeping the current around 25mA. You'll need a 25W resistor for that; 2 x 5k 12W Mills in series or 2 x 20k in // would be fine.
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