I have included these testers on this site as there seems to be little or no information about it on the web.
The unit has sockets for the American type valves generally found in Australian domestic radio and TV sets; namely UX4-7, International Octal, Loctal and the B7G and B9A miniature types. There is a row of three empty positions for additional socket types. It caters for 20 different filament voltages. Essentially the unit tests for filament continuity, internal shorts and emission, these being sufficient to check whether a valve is satisfactory for normal radio use. A comprehensive list of settings for about 1000 valve types is supplied as part of the manual. With this to hand, the unit is simple to use. No mains switch or pilot light is fitted but could be added.
Click to see
The circuit diagram. In later models the Merit switch is rewired so it isn't used for the Shorts test.
Here are the Operations Manual and Valve Settings and a couple of front covers to choose from, the original and my version in pdf format.
An advertisement from the July 1959 issue of Radio, Television & Hobbies
Transconductance testers such as the AVO Mk IV or CT160 are much sought after, particularly by audiophiles who require closely matched valves in amplifiers, resulting in them often fetching very high prices. A TVT, although apparently not very common, can be acquired for a small fraction of the price of these precision units.
Value is affected by general condition and a manual with settings is almost essential to give the correct 'Range' setting.
Work done after acquisition included some cleaning, switch lubrication, replacment of two missing knobs and obtaining the manual. On testing, I discovered that the Shorts test showed a bit of leakage with some electrodes when valves were hot. The fault was traced to the 0.05mf capacitor (see circuit) which measured 0.2mf, allowing enough valve current to flow to partially light the neon bulb. The capacitor was replaced and it now works well.
I no longer have this unit as I have another tester, so can give little more detail than is on this page.
Count since 1/7/07.