I used Kara Chaffee to fix my TV3, but she quit working on them a few years back. I don't know anyone on that side of the country. There are manuals available with calibration procedures for almost all the Hickok testers. As for the 600, you might just have some out of spec resistors for the line adjust. Unfortunately, every test relies on an accurate line adjust. Here's some info from the manual.
ADJUSTMENT CHART
1. LINE ADJUST: The 150 volt plate supply is used as the reference when setting the AC line voltage adjustment. The AC
line control is adjusted until the plate voltage is 150 volts as read on the meter. All of the other operating voltages follow
along and are assumed to be correct. If the plate supply is abnormally high or low then adjusting it to the nominal 150 volts
with the line test will cause all of the other operating voltages to be shifted. This is because the line adjust will be
compensating for an abnormal plate supply and also affecting every other operating voltage.
If the plate supply voltage is normal and all of the other voltages are wrong by the same percentage, look at the
plate supply for problems. If the AC line test circuit itself is bad the plate and other voltages will all be wrong. If the plate
and other voltages are not correct after setting the AC line adjustment, check the resistors in the AC voltage metering
circuit R24 and R25. Also check the meter movement and verify that it indicates full scale when passing the nominal full scale current.
Older testers used a 1.4 milliamp movement with 80 ohms of resistance. Later versions were 500 microamps and 233 ohms
of resistance. Other values may have been used as production changes were made through the years. The metal plate
mounted on the side of the meter is a factory applied magnetic shunt. By loosening the mounting screw and sliding the
plate back and forth, small adjustments can be made to the full scale deflection of the meter. Bear in mind though that
changing the meter adjustment will effect the mutual conductance reading too so rule out everything else before adjusting
the meter.
