When I first began my radio hobby several years ago it was my good fortune to attend the annual Orlando winter "Hamification", the largest in the state and probably one of the largest in the country. The tailgater's area alone was close to that of the Foothills swap meet in California except that parking is free. I have not been to Elgin or Dayton (yet) but from what I hear, Orlando in February is not far behind.
One of the targets of my search was a tube tester. I really did not know much about them at that point except what I had learned in the rec.antiques.radio+phono (RARP) FAQ list. This could be summed up with "Emission testers are not any better than a VOM, what the True Believer needs is a Dynamic Mutual Conductance tester." Right.
This lead me to a search for just what the heck Dynamic Mutual Conductance is. Near as I can tell, most pump 60 hz AC into the grid rather than DC. With DMC comes a need to measure it: MicroMhos. Firstoff, a Mho is an ohm turned upsidedown. Instead of measuring resistance, it is a measure of conductance. Tubes amplify - that is a change (transient) in the charge on the grid results in a change in the number of electrons flowing to the plate (transconductance) has dimensions of the quotient of a small change in palte current divided by the change in grid voltage. uA/V and termed microMhos (Gm). Better tube testers provide readings in Gm for comparison with the tube specifications. Easy to use tube testers often just use Replace-?-Good scales. Some have both.
Alfred Gharardi in "Modern Radio Servicing" describes the method as superior - however in three chapters devoted to tube checkers, there is one paragraph on DMC. While he states that "Commercial tube testers employing this method of testing are available.", none are listed in the chaper devoted to commercial models. One model does reference Mutual Conductance - a ReadRite 421-422 - the included schematic is remarkably similar to the "Diamond Point Jr." that will be discussed later.
Having been told from a number of sources that Hickok was one of the bast of the "mid-range" commercial units, I set out to find one.
As I wandered, several were spotted, Supremes, Mercurys, Heathkits but none that said "Dynamic Mutual Conductance".
Finally I was fortunate to come across a Hickok model 533A. This was a beautiful unit both inside and out with what appears to be a rosewood finish on the wooden case (have since found out that the wood case is unusual in a post-war tube tester but there is no evidence of a covering having been removed - even under the rivets for the latches and hinges). Almost too pretty for commercial use. It provided for all the tests I needed including the four pin socket necessary to test the 83 - virtually all modern Hickoks have two tubes - four pin (same as 01A which it can also test) 83 and five pin (use octal socket) 5Y3 - is interesting that the late model 6000 series usually are found without the accessory adaptor for four pin tubes - caveat y'all.
At any rate, the 533A followed me home that day providing yeoman service as I built my collection of TransOceanics and companions. One of the things I found was that an easy way to separate class testers from the not-so-great was in the tube socket to knob ratio. Units that had more sockets than knobs generally were of the drug store tester type while more knobs than sockets was a plus. Multiple meters was a double plus. Two man lift added another star (why I like the TV-2 so much - a real boatanchor).
To me the 533A is a triumph of functionality. True being a late 1940's design it lacks some of the later socket types such as compactrons but everything Zenith used through 1960 is there. Like virtually all Hickoks, it is at least in theory, portable. There is a lid and there is a handle, but no sane person would want to carry it very far. The size does make for a spaciousness of design not present on some of the later units and the exposed positions are easier to turn to than the windows used on some later models.
Over the years I have looked at a lot of other testers such as Supreme & B&K but none had the combination of features that Hickoks do. As with anything else, there is an exception - the Sencore MU-150 Continental - a compact briefcase with a lot of sockets but which promises DMC. Unfortunately it had no DMC settings for the "1"s (1U6, 1R5, 1AC6...) tubes I test most so it was swapped for a Royal-7000.
Inevitably, the day came when there were enough TransOceanics, Meridians, and Globals around my house and the web site was fully populated with more than you would ever want to know about TransOceanics. Being somewhat insatiable, my interest turned to Hickoks and I began acquiring good examples (one of my requirements is that all my toys function). One factor is that as I began, good tube testers were relatively inexpensive since few could tell the difference between good and cheap 8*) which holds prices down.
The first addition was a 539A (before I knw the difference between a 539A and 539C) followed closely by a Navy TV3-B/U of 1952. Since then they have been joined by a 534A, 600A, 605A, USM-118B (CardOMatic), 752, and 799. Also there is a TV7D/U which, though obviously a Hickok design, I have not been able to determine who the manufacturer was (meter face, usually an indicator, says "Phastrom Ruggedized")
But it was the discovery of a Hickok "Diamond Point Jr." at a tailgater in Maryland that turned a mild intrest into an avocation. This appears to be one of the earliest tube testers with the Hickok name - no roll chart, selection of filament voltage and socket is by a listing over each. Only 81 tubes listed with the latest being the 6A7 (1934) would probably make this unit a 1933-34 model. Help from Alan Douglas further narrowed this to NLT early 1934. Is interesting to note that the unit has no evident model number and is identified only by the serial number tag and the meter face inscription. Advertisements (see other page) indicates that it is most likely a J-34 (J for Junior) though is probably earlier since it lacks the top row of sockets and the 12.3v filament setting of the J-34.Two meters (no marking except a line on the smaller - suspect is line voltage setting). No tubes. No rectification evident. Will require restoration before can determine exactly what it does but appears very similar to the ReadRite mentioned by Ghirardi. For a random selection of model numbers and dates see the model and date page