Set mechanical zero first.
Warm-up for 15 minutes.Current:
Set Selector to "Current" & Range to "50mA". Connect black to -Current and red to +mA.
Deliver exactly 25mA to unit and adjust R14 to half-scale (ed - this is probably a superfluous step)
Deliver exactly 50mA and set R14 for 50mA reading.
Check full-scale of all ranges for +/-3% accuracy.
Move red to +1.5Amp
Supply exactly 1.4 Amperes. Should read between 1.37 and 1.43 A. DC Voltage:
Selector to "+Volts" Check line voltage for 117V, 60 Hz.
Set Zero Adjust for reading of zero. Do not re-adjust during rest of calibration procedure.
Set Range to "50V". Supply exactly 50 Volts to the ground terminal and probe.
Adjust "+DC Cal," R15, for reading of exactly 50V.
reverse lead connections with selector set to "-Volts."
Adjust "-DC Cal," R13, for a reading of exactly 50 Volts. AC Calibration Check:
Remove the WG-217 DC Probe from the WG-218 Direct Probe and Cable.
Set Selector to "AC Volts." Set Range to "1.5" Volts.
Short direct probe to ground clip and adjust "AC Zero," R47, for a reading of exactly Zero. This pot is at the rear of chassis and is adjustable via an opening at the rear of the cabinet.
Turn "Range" through the scale settings and verify readings are zero. If not, swap or replace 6AL5s.
Set Range to "150." Apply exactly 150 VAC, 60 Hz, to the direct probe. The meter should read within 5%. If not, verify circuit component values. AC Compensation Adjustment:
Set the Selector to "AC Volts," & Range to "500V."
Zero pointer (ed - should already be there!)
Apply exactly 200 VAC, at approx. 100 KHz, between Ground and Direct Probe.
Adjust ceramic trimmer C2 for a reading of exactly 200V. Ohms Adjustment:
Note: Battery must be installed for resistance measurements.
Set Selector to "+Volts" and verify pointer is at zero.
Set Selector to "Ohms" and Range to "RX1."
Adjust the Ohms Adjust for full-scale deflection.
Set Range to "RX1MEG." The meter should read above 1000. A reading of less than 1000 indicates excessive leakage in the resistance circuit.
If necessary to readjust "Ohms Adjust" when changing from RX1 to RX1MEG ranges, verify battery voltage.
I have an original manual to go with mine.