As you’ve likely figured out, I am a bit of a hoarder and my areas of focus run the gamut but often involve things of a vintage, historic, or technological nature–preferably a combination of the three. As mentioned previously I not only collect, but restore, use, and learn from many of these items. ….and sometimes I even manage to part with few so as to fund my curation of other similar items. (hey, I did say I was a bit of a hoarder…….or perhaps my wife told me so….in any case, it is true……but at least I don’t have a pile of garbage with a hundred cats fighting over the edible scraps.)
I have a special place in my heart for science related instruments and tools, especially those intended for teaching. St Louis motors, Van de Graaf generators, steam engines, meters of all sorts, etc, etc. I am always on the lookout for such things. I recently ran upon a Cenco (Central Scientific Company) catalog number 80420 “Vacuum Tube Demonstrator” apparatus. This appears in an earlier form in my 1937 edition of their catalog (yes, I collect the old big hardbound catalogs too)…
The version I have is from 1944, according to the date on the instruction sheet. Yes. 1944. During the war. A time when only those items deemed necessary to the war effort were produced. This item obviously made the cut–not surprising given the effort and emphasis on electronics and training of people in that field. The atom bomb may have ended the war, but RADAR won it, and neither would have been possible without advances and creations of new technologies. This is a simple yet effective device for illustrating basic vacuum tube principles. Other websites I have found mention this unit, but not in much detail. Hence part of my reason to bring it to this page for you.
The unit consists of a tube socket, in the early version a 4 pin, but in this version an Octal socket primarily intended for the recent (ca 1940/1941) 6J5 Triode tube.
It is mounted along with filament and grid voltage control rheostats, a reversing switch to allow positive or negative voltages to be applied to the grid, and an assortment of binding posts to connect power supplies and meters to measure voltages and current flows. Perhaps best of all, the unit has the schematic graphically illustrated right upon the panel so the student can readily see what is going where and easily see the effects of varying one parameter or another during the operation of the experiments. In so doing one can–with some patience–plot a graph of the specific tube’s characteristic curve. (Lacking a Tektronix 570 or other vacuum tube curve tracer a person could, with lots of patience, use this thing to plot curves of all manner of other triodes by simply altering cable leads and power supplies to suit the need of the tube under test!)
Following through the printed out experimental process, it becomes possible for the student to fully understand the ramifications of minor changes in circuit parameters and even, to a lessor degree, the possible effects of alterations to the construction of the tube itself. (such as the possible effect of a change to the spacing of the internal elements or to their physical configuration–flat plates, round plates, spiral grid vs a screen, etc, etc) Granted, this goes a bit beyond the intent of the primary purpose of this device, but if a student is sharp they would likely begin to make the connections……..and, hopefully, a contribution to the state of the art at the time. It also seems to me that one could even use it in conjunction with other circuit elements to help breadboard design complete radio or amplifier type equipment on the lab bench.
No doubt this, and other similar devices found in physics classrooms of the era, helped to not only train engineers and technicians for wartime needs but also lead to the creative solutions that brought about the explosion of advances that were made after the war right up into the era of modern computers.
Lastly, for those who might wish to read further or who have one of these in their own collection and are seeking the instruction manual, here it is for your perusal…