The mystery of the lost data sheet of the VT52 tube.

This is a portrait of a tube, of which the data sheets were hidden for ever, and probably must be considered lost. The only small hope we have left, is for some copies, illegally made at the time, which may pop up from some collector's junk files. So not much of a hope. Just suppose some crazy old uncle dies, leaving behind his strange equipment, boxes full of things and tube stuff, old magazines and just a lot of mess. The loose documents get thrown away, and that's it.

I think only just a few persons may be still alive from the days where they were involved in VT52 designs, and perhaps none any more. So chances something pops up are closer to zero. This is why I think, military data was successfully destroyed, as it should have been done anyway, and no illegal copies were made. So far, for my assumptions. The only thing we know for sure is, we don't know it. (quote by Socrates).

VT52 was intended for military use, and some pieces of equipment, where it was used for, have survived the times, as well as the tubes we find with collectors. These are expensive, but apart from the price, can be found easily. From well preserved boxes even, we get at least data about the the production period, brands, some internal references. The tube data which we can still subtract from NOS tubes.

The only document known to have existed, was by the mil spec MIL-E-1/377, in which the tube had the Navy internal designation 38145. It was given an ordinary VT number, like so many VT tubes. So what we may be looking for is the 38145 data sheet perhaps, and not the VT52 data sheet.

The assumptions

When making assumptions, it's ok when you say that's what you're doing. But it's wrong saying this what you know, and in the end it's just copied babble from others. So is the VT52 a "special 45"? My correct answer is: I don't know that.

Since the data and shape resemble the 45 tube, some call it a "special 45", where the specially is supposed to be the adapted heater voltage. But I have seen no evidence to support this. I read on a forum another possibility. Someone said, it may as well be a modified VT25A, of which the grid was changed, an a Barium cathode was used. That would also result in something like the VT52. So the assumption, it must be a modified 45, because that's the only possible option, at least is invalid.

We have the number VT52 on the socket, but no data sheet for the generic part number, which is said to be 38145 by some. Now such a five digit number can not be invented easily, or by mistake. So some probability this may lead somewhere, exists. Though so far, there is nothing.

Heater Voltage

The strange heater voltage of 7 Volts, results from specifications of a 6.3V car battery. There are two way to use such a battery: Charge it and use it like that as a heater battery, which was very common at some times. Then you have 6.3V +/-5%.

Another way to use a car battery, is on the car itself. Then we have 6....6.6V with the engine off. Now, older cars had DC generators, which by their working principle need a rpm above idle, to begin charging the battery. So we talk about 6.6V in idle, assuming the battery is charged, or 7.5V at full rpm. This means the tube must work at 7V, 7% tolerance. This 7%, instead of the maximum 5% for DHT, is fair enough the battery can have a mixture of charge conditions, and it is never continuously 7% off. So that works, and it showing the intention of the VT52, it was designed for engine powered vehicles with a 6.3V battery system.

What we do know.

VT52 had the EIA designation 2C45. Unfortunately, 2C45 was never registered, and this designation leads not any further.

We do have some old documents, which at least sum up some numbers, but these are not consistent.