This is my current go-to-tester. I acquired this tube tester from a Customer and it has been calibrated and several enhancements added. This is a very clean tube tester and doesn’t show much wear at all. The case has a few scuffs, but is overall in great shape.
I converted the tube rectifiers to solid state, and added a lamp holder with a #49 bulb as a fuse to protect the Bias pot. Converting to solid state rectifiers affects the calibration and some circuit modifications have to be made to accommodate the lower filament load on the transformer. The #83 tube is getting harder to find and is getting expensive. Converting to solid state rectifiers cuts down the filament load on the transformer and the heat generated. This will help extend the life of the transformer and the tube tester.
I recommend adding a Bias fuse bulb to any tube tester that does not have it installed originally. This protects the Bias pot if the Bias current gets too high. The Bias pot is no longer made and there is no replacement available.
Several enhancements have been made to this tube tester to enhance the accuracy. I do these enhancements when I calibrate a 539B or C tube tester.
The meters in this tube tester are original and are all within specifications.