14-07-2022, 10:27 PM
Hi.
Connect your DMM negative to the cathode and the positive to the Control grid G1 and see what it's voltage is, it should be negative.
Also if the cathode volts are say 13v and the resistor is a 220 ohm the total current will be 59ma, which is too high IMO, if the cathode resistor is 470 ohms with the same 13v it'll be 28ma, now much lower. So we need to know what the grid volts are in respect to the cathode. Ideally to measure the grid you need a high impedance meter for this most DMMs are pretty good TBH so we know the cathode is X and we measure the grid as Y. EG, X=+13, Y=+1 so Y-X= - 12v so in fact we have our correct negative bias on the grid. Looking over the thread the problem you have might not be too bad. Reading between the Grid and Chassis doesn't necessarily give you a reading at zero, tiny leakages can give readings. Hope this helps
Connect your DMM negative to the cathode and the positive to the Control grid G1 and see what it's voltage is, it should be negative.
Also if the cathode volts are say 13v and the resistor is a 220 ohm the total current will be 59ma, which is too high IMO, if the cathode resistor is 470 ohms with the same 13v it'll be 28ma, now much lower. So we need to know what the grid volts are in respect to the cathode. Ideally to measure the grid you need a high impedance meter for this most DMMs are pretty good TBH so we know the cathode is X and we measure the grid as Y. EG, X=+13, Y=+1 so Y-X= - 12v so in fact we have our correct negative bias on the grid. Looking over the thread the problem you have might not be too bad. Reading between the Grid and Chassis doesn't necessarily give you a reading at zero, tiny leakages can give readings. Hope this helps
