03-26-2013, 07:29 PM
Your new readings look reasonable. If you put the negative meter lead on the cathode and the positive to the chassis to measure the bias, you will get a negative reading since the cathode is positive with respect to the chassis.
Keep in mind that the original voltage readings on the schematic were taken with a relatively low input resistance mechanical analog meter, which loaded the circuits and made the readings seem lower than the actual voltage at the point being measured. A modern DVM will usually have a 10 meg input resistance, so the voltages will seem high in comparison when measuring high resistance circuits like the 57 screen grid pin, fed by a 3 meg series resistor.
The voltages with the replacement 57 seem more like what they should be. Do you notice any difference in performance?
Keep in mind that the original voltage readings on the schematic were taken with a relatively low input resistance mechanical analog meter, which loaded the circuits and made the readings seem lower than the actual voltage at the point being measured. A modern DVM will usually have a 10 meg input resistance, so the voltages will seem high in comparison when measuring high resistance circuits like the 57 screen grid pin, fed by a 3 meg series resistor.
The voltages with the replacement 57 seem more like what they should be. Do you notice any difference in performance?
