You can improve your tester with the addition of quality modern digital meters. Digital meters are important to improve the measurement accuracy of the tester. They are more accurate than the old analog meters and many of the old meters are further out of specification accuracy due to aging of the meters parts.
These meters are designed to mount into the tester's rear compartment as additional meters. They do not replace the original old analog meters. I have designed a meter assembly module that will drop in to the rear compartment. The added electronics are mounted in the electronic module.
Digital AC Line Set Meter
0.5% accuracy. Replaces old analog AC meter (+/-3.0% when new). For many testers these meters, due to age, are on average +/- 3 to 5% accurate. Upgrading to digital is a major improvement to increase the accuracy of the tester. This will allow the tester to more closely compare to measured results to other true Gm tester and to compare the test result to the tube specification values in the tube manuals like the 539B and the 539C can do.
Digital Bias Voltage Meter
0.5% accuracy. Replaces old analog bias meter (+/-2.0 when new) and again for many testers these meters, due to age are on average +/- 3 to 5% accurate. Upgrading to digital adds to the tester's accuracy and the ability to match tubes by knowing the actual DC bias voltage applied to the tube at test.
Digital Plate Current Meter
0.5% accuracy. Always in the circuit to allow for the measurement of plate current on any tube measured. This is necessary to allow you to correctly match tubes.
The Complete Set
Add all 3 digital meters for much improved accuracy. With this upgrade you can easily perform accurate power tube matching, and set the AC line set more accurately than possible with the original analog meter.