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06-01-2023, 07:07 PM
Hi Champ81
You said previously that you have TUT3. Please read the section about grounds. Chassis is tied to earth ground (safety ground) to act as a shield The chassis is not supposed to be used to tie circuit grounds to each other - it is strictly for shielding.
NO terminal on a device is "ground" unless you tie that terminal to the circuit ground.
A typical Volume control, MV or other level control is often connected to circuit ground at the pot-0 end. Without the bias control circuit, your stock cathode-bias output stage has a grid-leak tied to ground for each side of the circuit. These grid-leaks can be replaced by a dual pot with pot-0 tied to ground and wiper to the grid. Pot-X accepts the signal input.
With the bias circuit the grid-leaks are above ground, so if they are replaced by the MV, the pot-0 ends are above ground.
You can make the bottom of the MV (or grid-leaks) AC ground by adding caps across R12 and R13, which is also from each bias pot-wiper to ground AND MV pot-0 to ground. This eliminates the voltage divider effect of the grid-leak and the bias-pot, and therefore the volume change with bias setting.
You said previously that you have TUT3. Please read the section about grounds. Chassis is tied to earth ground (safety ground) to act as a shield The chassis is not supposed to be used to tie circuit grounds to each other - it is strictly for shielding.
NO terminal on a device is "ground" unless you tie that terminal to the circuit ground.
A typical Volume control, MV or other level control is often connected to circuit ground at the pot-0 end. Without the bias control circuit, your stock cathode-bias output stage has a grid-leak tied to ground for each side of the circuit. These grid-leaks can be replaced by a dual pot with pot-0 tied to ground and wiper to the grid. Pot-X accepts the signal input.
With the bias circuit the grid-leaks are above ground, so if they are replaced by the MV, the pot-0 ends are above ground.
You can make the bottom of the MV (or grid-leaks) AC ground by adding caps across R12 and R13, which is also from each bias pot-wiper to ground AND MV pot-0 to ground. This eliminates the voltage divider effect of the grid-leak and the bias-pot, and therefore the volume change with bias setting.
