This report tries to tell the story about the VT52 and all of it's relatives which were produced over the years. I will try to go into the history of the 45 leading up to the development of the 45A and 2C45/VT52 tubes. There is no other published information about these types that I am aware of, only some small notes on operating parameters etc. A great part of the information found on these pages is really about the differences between the different brands of this type made over the years it was in production. It seems there were quite a few people with their own ideas on how this tube should be designed. Information will be added to these pages as I get/find it... Enjoy... Appearance can be deceiving... A few years ago I bought some n.o.s. VT52's to put in my future power amp. At first I ordered 4 tubes from someone for a very fair price. They were three Senco's and a Philco but I was told these were in fact relabeled Hytrons and exactly the same. All 4 of them looked identical and relabeling was pretty common in those days, I saw no reason to question his statement. A few months later I bumped into some more VT52's but when I got them I noticed these were quite different from the ones I already had. This is not really a strange phenomenon in tube-land, each manufacturer's tubes had their own characteristics, just compare two different ECC tubes and you will see what I mean. A plate that was a little different than the other, or a different getter... No real problem with that, but I noticed the plate and getters were not the only thing different. The 4 tubes I had bought earlier all had a filament made up of three V sections, but the new ones I had just received all had only two of these sections.
Another point of difference between the two types of Hytrons were the anodes. The ones with the triple filament sections (Senco and Philco) had slightly shorter plates with the grid sticking out several windings below it, the Hytrons did not. The anodes of the Hytrons were held in place by a mica suport on the top and bottom of the plate, the Senco and Philco only had one at the top. There were some other differences as well between these two types, more info can be seen on the physical traits page.
Now I don't mind a different plate, the tube will still have about the same specs. But a totally different filament is another matter. I have seen many variations in structure in 45 tubes, almost no one tube is the same as that of another manufacturer's. But even these all had the same type of filament. What's the deal here I wondered. Still getting over my curiosity about this little discrepancy I ran into a TungSol VT52. I wondered which kind of filament this one would have. When I anxiously opened the package, like Christmas all over again, I was even more amazed to find a tube inside that was the size of a regular 45ST. "Nah! They suckered me!" I thought until I looked at the printing on the tube. It said VT52 all right, even the original box it was in. All the other tubes so far had the same ST16 glass envelope as the 2A3, 10 etc, but the TungSol was the size of a ST14 (45ST). Another surprise was the plate which was just a tad longer than an ordinary 45's and the black paint on the inside of the glass. "What the heck is going on here!!! Which type is the real VT52, and which the copy?". Out of the 9 or 10 odd tubes I had collected so far, almost all were different from each other, only the Philco and Senco's seemed to be identical.
I recently received some photo's from James Dowdy who had a friend that owned a Raytheon VT52. I was curious as to how other brands looked so I received a copy. The Raytheons had "4 pillar box-plates". This is a very curious looking construction which I can't really make out out of the pictures. The tube has massive ceramic supports on the top and bottom of the plate. So yet another different structure, that would make 4 out of 4 different types of VT52. Strangely all reportedly had the same electrical specs. I later got hold of a pair of these strange box-plated VT52's myself, they really are a catch!
In the picture of the Raytheon there were a few tubes as reference in size. One picture had a line-up of 3 tubes. A VT52 and two normal 45 ST's I thought at first, but one turned out to be a 45A. I never heard of this type before I saw the picture. It turned out the 45A was an uprated version of the 45 with a higher anode voltage and anode dissipation. The 45A's internal structure looks identical to a regular 45, only the glass was now a larger ST16 like that of the 2A3 etc. The picture clearly shows that the 45A is somewhere between the VT52 and 45 in size. I got some parameters from my AVO manual which lists a similar filament voltage, so this tube is not a VT52 which is what I first thought. I find that this tube is a lot harder to get than a VT52 which makes you wonder if it was really made for a long period of time. I've seen about 100-200 type 50 tubes offered in all shapes and sizes, but not a single 45A... It seems the 45A filled a gap between the normal 45 and the 50 for power and operating conditions. The increased specs of the 45 allowed it handle 15W on the plate with a maximum voltage of 325V. This tube could get 2 to 2.5W of power in comparison to the 1.6W of the normal 45. I think the production run for 45A's was very limited since bigger and more powerful tubes took over from this point.
Light my fire... I had a pair of Western Electric types in my hand an noticed how they were identical to the Senco's and NU that I recently got. Same "VVV" filament, same mica, same anode, same glass.... The data for the filaments however were very different. Only WE was known to be 7V/1.18A, all the others were said to be 6.3V/1A. This seemed very strange to me... why would WE make their types with 7V heaters while all others used a 6.3V filament, makes no sense at all. No one has been able to give a reason for this deviation in WE filament specs. It is unclear to me if the 7V which given value should be the correct one. Someone also pointed out to me that Sylvania listed 7V in their data manuals, but I am wondering if they were following the trend or if this was the real filament voltage. Only this weekend did I make the connection as to how this data may have come into the world. I was looking through some equivalency tables and found under 45-Special an equivalent named 2C45. Aha... note 1:
The 2C45 is a transmitting triode with a 7V 1.18A filament (does this ring a bell?). The 2C45 is based on the original 45, although with a 7V filament for extra emission for use in transmitters. I haven't been able to find out if the 7V filament is a thoriated tungsten- or normal oxide filament. So far I have come across 2 sources giving 7V for the WE type VT52, and two other sources listing the 2C45 (also 7V) as an equivalent tot the VT52. It's beginning to seem that 7V might have been the actual voltage for the WE and NU produced VT52's. Ludwell Sibley's book "Tube Lore" gave some interesting info that I had not seen before. His research into all kinds of tubes came in handy in my own search for knowledge about the VT52. Under 2C45 he states: "2C45 [AKA 38142, 45 Spl., VT52]; xmtg. triode, 45 w/ fil. 7V, 1.18A, made by NU under WE contract for BC230/430 aircraft radios; also distributed by HY <4D>". HY here meaning Hytron. Along with this info and the info I found in an old dutch tube vademecum, it seems the National Union 2C45 is actually the same as a Western Electric VT52. This started me thinking: the NU VT52 that I have is identical to the WE VT52's I've seen so far, as are the Senco and Philco types. This leads me to believe that the Philco and Senco's all have the same manufacturer, but not Hytron; I believe National Union made them instead. Western Electric contracted NU to make the 2C45 for them (which was labeled VT52 for military use) and it was common in those days to buy tubes from a factory and put your own brand on them and sell them. This also explains the Philco and Senco logos on the tubes I have. My conclusion would be that Western Electric, Philco, Senco and National Union VT52's are all the exact same tube and used at 7V. This would also explain the filament consisting out of three V sections against the double-V sections of the other brands. Would this explain the filament voltage difference? I gave this info to a friend, Erwin Wiesbauer, who uses the WE VT52's in his own amps. He was generous enough to try my idea of putting 6.3V on the filaments for a change. He told me the current at 7V was not the 1.18A as supposed, but around 0.9A. Currents usually differ a little from the nominal value, but 0.3A is too much for any tube. After getting 6.3V across the filament he reported he saw no, or almost no decrease in the color of the filament; still the same orange. If the tube would really be a 7V filament, it should change color more drastically than this. Just try it with a 6A3 and you'll see that at 5,5V it is already turning red instead of orange. I am still waiting to see what current are flowing at this voltage in the WE. This experiment seems to show that the NU tubes can be run at 7 or 6.3V without any penalties. The lower setting even increases life expectancy. Moral of this story: |
