I am repairing this meter for a customer. I looks like it has taken a high voltage hit at some time. I have the basics of the meter working. Some resistors have gone very high in value and need to be replaced, some have been replaced in the past and are the incorrect values.
In tracing out the circuits i find that R-9 is missing in the circuit and Pin # 1 of the 6SN7 is connected directly to chassis ground. I plan on installing a 5 Meg. resistor between Pin 1 and chassis ground as the schematic calls for.
With the grid taken directly to ground what effects would/should i see in the metering?
Thank you,
Mitch
Mitch:
The electrons from the cathode hitting the grid, and working their way to ground through the five meg resistor will cause a negative bias on the grid, which will not be there if the grid is connected directly to ground. The 6SN7 and the zero pot are acting like a balanced bridge, with the Voltage divider chain acting as the grid resistor for the other side of the tube. Without the five meg resistor, you will probably not be able to get the bridge to balance, therefore never getting the meter to zero without an input.
Lewis
Lewis
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