Unless the thing has been just used to death the bias and english potentiometers are pretty reliable. They may need cleaned, but the backs are open so it's easy to get to the windings. The main thing you want to do is replace the electrolytic caps if they are the originals. Ticking time bombs at 50+ years old regardless of usage. Been a long time since I did mine, but IIRC there's only 3 or 4 in there that need replaced and they're very easy to get to. Get the values off the caps themselves if you can -- Hickok was famous for making circuit modifications without updating the manuals, so the parts list in the manual may or may not be accurate. Basic soldering skills are all that's needed. Avoid DeOxit like the plague inside these testers. It leaves a residue that can soak into the phenolic wafers the rotary switches are built up from and will become conductive over time destroying the accuracy of the tester. As a general rule, if a switch or pot (rotary or up/down) is working correctly and smoothly, leave it alone. Only clean and/or lubricate if the action is rough or moving the knob or pot causes things to jump around unpredictably. Also, don't plug it in and fire it up as soon as you get it out of the box. Type 83 tubes don't like being jostled around and need time to settle. Let it sit and take in its new surroundings for at least an hour. Why the 83 tube was used so widely in these testers (and not just Hickoks) is very strange, as most of them were designed to be portable and the 83 wasn't. I don't want to go further off-track in this thread so I'll quit here, but if there's anything else I can help with shoot me a PM.
I think the B65 might go back on eBay.
