Hickok 209A VTVM Restoration Part 5
This the fifth part of an “N” part series documenting my restoration of the Hickok 209A VTVM, SN 1333254. Hickok 209A VTVM Restoration Part 5: Checking the meter movement.
This piece of test gear is all about the large, beautiful meter movement, so I need to determine if this one works properly. What I intend to do is connect the meter to a precision power supply and good ammeter through a current limiting resistor and then determine how the meter responds. The meter is supposed to be a 500uA full scale movement.
Here is the test setup:
A 10kohm limiting resistor is connected in series with the power supply. The power supply is a Tektronix PS5004 and the meter is a Tektronix DM5120.
Full Scale Deflection on the meter was about 497 uA:
I recorded the meter current at intervals of 1/6 scale deflection:
The additional columns in the spreadsheet are the Ideal Current which is the current through a perfect 500uA movement at a given deflection. And the Real Current, which is the current that should flow through the meter, based on the measured FSD current.
I plotted the data in Excel as follows:
Although the resulting measured current plot is very close to being a straight line (Trendline R2 = 0.9994), I am not sure what that means in terms of the meter linearity once it is installed into the meter circuit. However I have verified that the meter movement is smooth, readings are repeatable, and it appears to be reasonably linear.
Part 6 of this series will cover evaluation of component condition and the plan for component replacement.
Thanks for reading.