02-10-2017, 08:34 AM
Morzh, you bring up an important point regarding measurements taken with a 1000 ohms per volt meter. It is really dependent on the series resistance of the circuit being measured.
For example, lets say you are measuring the plate circuit of a 75 tube triode audio stage. It has a 100K resistor to the B+ supply and you are using a 1000 ohms per volt meter on the 100 volt range. The meter has an input resistance of 100V times 1000 ohms/V = 100K. Now you connect the meter to the plate of the 75. You have now created a voltage divider of two 100K resistors between the supply and the the meter. So in this case the meter reading is only half the actual voltage or 50% low.
Now take the case of measuring voltage after the field coil which has a 1K resistance. You still have a voltage divider created when you connect the meter. But in this case it is a voltage divider with 1K and 100K resistors, so the error is only about 1% in this case.
For example, lets say you are measuring the plate circuit of a 75 tube triode audio stage. It has a 100K resistor to the B+ supply and you are using a 1000 ohms per volt meter on the 100 volt range. The meter has an input resistance of 100V times 1000 ohms/V = 100K. Now you connect the meter to the plate of the 75. You have now created a voltage divider of two 100K resistors between the supply and the the meter. So in this case the meter reading is only half the actual voltage or 50% low.
Now take the case of measuring voltage after the field coil which has a 1K resistance. You still have a voltage divider created when you connect the meter. But in this case it is a voltage divider with 1K and 100K resistors, so the error is only about 1% in this case.
