The Knight tube tester shown in this photo needs an overhaul. From reading the posts here I think it's a 1955 vintage, as it has no model number (in fact, I can't even locate a catalogue number). Trying to locate a manual, once I can positively ID it. If it is indeed the first edition of the 600 series, will a manual from a later model (600A etc) work? Thanks!

It sure looks like an early styling of the 600. I'd get a 600 manual and compare it to what you've got. Even if it's not identical inside it is probably close enough to make sure yours is working properly

You're Knight tube tester shown is a 83YX143 there is a manual at:

https://www.radiomuseum.org/r/allied_ra ... yx143.html

The 83yx143 differ than later 600

The Triplett 2413 and 3413 is what the Knight Kit Tube Testers are base on, in fact Triplett made
some of the or all Knight Kit tube testers.

From a number of posts it has become apparent that the roll chart or charts for the Triplett 3413, EICO 625, Heathkit TC & IT and Knight 600 (all simple emission testers) have the same settings for the tubes but may have, as pointed out in one of the posts, different switch configuration. I believe the the Knight used letters as opposed to numbers for the switches which correspond to the pin numbers of the tubes (9 & 10 on the EICO being grid caps). The columns for the tube chart (and switch settings) are "Tube Shunt Fil Sel Up Down". The Up, Center and Down on the pin switches are Center position = Filament Voltage, Down = Common (Gnd/0 V.) and Up = Positive DC V. On other models, if you know which position equals the above on your unit, you can interpolated the settings to suit the unit.