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05-30-2023, 11:54 PM
Hi Guys
The DC isolated MV is simple to wire: pot-0 goes to ground, pot-X goes to the splitter cap and pot-wiper goes to a new cap tying into the output stage with its bias controls. Within that circuit, R2,4 remain as fixed values. This is the same as you do for a fixed-bias amp post-PI-MV.
In any tube circuit, you can see the grid voltage if you have one meter lead at the cathode of the tube and the other on the grid. In many circuits, measuring grid voltage from ground is not accurate as the meter resistance changes the biasing. You have to remember that in the bias circuit above for cathode-bias, we are creating a little extra voltage range so there will be adjustment. You should find that taking one tube or the other down from maximum by just a tiny amount will balance the hum. The amount of control voltage available will change as you change the idle current in either tube.
In fixed-bias, the raw bias supply is itself considered to be constant, and it is not effected by the pot settings or the tube currents. That makes the bias pots less interactive than in this situation.
The DC isolated MV is simple to wire: pot-0 goes to ground, pot-X goes to the splitter cap and pot-wiper goes to a new cap tying into the output stage with its bias controls. Within that circuit, R2,4 remain as fixed values. This is the same as you do for a fixed-bias amp post-PI-MV.
In any tube circuit, you can see the grid voltage if you have one meter lead at the cathode of the tube and the other on the grid. In many circuits, measuring grid voltage from ground is not accurate as the meter resistance changes the biasing. You have to remember that in the bias circuit above for cathode-bias, we are creating a little extra voltage range so there will be adjustment. You should find that taking one tube or the other down from maximum by just a tiny amount will balance the hum. The amount of control voltage available will change as you change the idle current in either tube.
In fixed-bias, the raw bias supply is itself considered to be constant, and it is not effected by the pot settings or the tube currents. That makes the bias pots less interactive than in this situation.
