Very hard to find Western Electric KS-15750-L1 L2. Marked as L1, but has the extended settings which the L2 has of 1200 and 600gm, you can see the added section at the lower right side.. If you use Western Electric you really need a tester made to test them. For WE tubes requiring "self bias" the jack is the for the resistor. We can order them easy enough, with 1% accuracy, if you need them
It was rebuilt as needed and calibrated just a few months ago by us, c.g.industries. The bias meter was bad so a Datel MuRata digital meter was installed which is much more accurate and has it's own independent power supply. The bias pot was erratic and difficult to hold the bias number, so that was taken apart, cleaned, treated, and restored to a highly stable condition. Bias now is rock solid and steady, and when you have to set something like a 12ax7 at 1.1 volt, you will immediately appreciate the accuracy you can not get from the old way. Both 83 and 5Y3 tubes are NOS, solid state modules do not always work very well in Hickok, so the tube method stayed.
Plate current jacks were added to the upper left edge. Any multimeter with a "millivolt" setting will be able to read the actual plate current ( no screen is measured on power tubes so the reading is what the manufacturer would use). Photo shows the current on the tested tubes. Your multimeter does not have to set on the tester, it is there for picture compression.
The deck is excellent. The case less a mar on the side, is excellent in MY opinion for something from the mid 1960's. Copy of the manual is includes, operation is simple. Picture show a 12ax7 Fisher/Holland and a Sylvania 6dj8.
After the sale help is always available.