Tube Socket Information

Tube Sockets	Page 2 of 7

History of tube sockets (primarily in the United States)	Page 2 of 7

Octal Developed	Page 3 of 7

Loktal Sockets	Page 3 of 7

Other Octal Sockets	Page 4 of 7

Miniature Types	Page 4 of 7

Novar and Magnoval Sockets	Page 5 of 7

Compactron Socket	Page 5 of 7

Nuvistor Sockets	Page 5 of 7

CRT Sockets	Page 5 of 7

Transmitting Tube Sockets	Page 6 of 7

Foreign Receiving Sockets	Page 6 of 7

Tube Sockets & Their Configurations

This was written by a retired engineer who wishes to remain anonymous.

Tube Sockets

In considering the sheer number of tube sockets in existence, well into the hundreds, it would seem as if it had been a deliberate attempt by designers to cause confusion and require that a lot of different tubes and sockets be made unnecessarily. For the most part this isn't true.

From the collector's viewpoint, this rich history means that one could make a pretty good hobby merely of collecting tube sockets, together with an example of tube or other item which would fit correctly.

Manufacturers of tube testers were probably most directly impacted by this cornucopia of socket types, with no one tube tester being able to test every or even 99% of tube types that would be encountered in practice without aftermarket modification or adapters.

In general manufacture of new equipment, of course, at any one point in time there never were more than five or six types of sockets which were terribly common.

It is also important to consider that the American, British, and Continental European markets were all substantially isolated from one another, although the sheer industrial abundance of American electronic manufacturing meant that what was really popular in the United States, was also available in some quantity everywhere on the planet. Whereas German, Dutch (Philips) and British equipment was sold in the US on only an intermittent and limited basis, primarily postwar.

On the other hand, only two types of tube bases, or sockets are in common use at this time except for transmitting tubes. These are the nine pin miniature and the standard octal.

History of tube sockets (primarily in the United States)

The earliest tubes such as the DeForest Audion were manufactured on light bulb machinery and used lamp bases and flying leads. A variety of leads, clips and fittings came into use but it soon became apparent that a base with multiple contacts which the tube could be inserted into was the simplest method of connection. Since tubes consisted entirely of filamentary diodes and triodes, four was as many contacts as was needed and so four pin connectors became the earliest standard. Although several proprietary sockets and tubes were introduced such as the Westinghouse WD11, the first standard basing was the UV four pin base. It had four short nubby pins and a bayonet pin on the side which was for mechanical purposes and was fitted in the socket like a bayonet. Later, the UX base was invented with four long pins in the same spacing and order, so that the tube could simply plug in downwards (assuming the socket was horizontal facing up). This base is still in use on the 811 transmitting tube, the WE 300B and for some industrial and medical electronic uses. Some tubes were designed so they could be used either in the UV or UX ("regular four pin" to us) bases and have both long pins and a side bayonet fixturing pin. UX bases are still made and common. (WE and commercial bayonet sockets had a different orientation of the pin slot. The 300A and 300B are identical except for the orientation of the pin slot so the 300B would fit a certain older WE ERPI unit and sub as a power tube or, with a jumper, a rectifier!-B)

The UY five pin base was next, introduced because of the need for three separate pins for the heater and the cathode. Screen grid tubes came out at this time also and most of these had a top cap for the control grid at first. Six pin sockets were next and were used for pentode tubes and multi-section tubes: the most well remembered use for many hobbyists was on the 6E5 seeing eye tube. Seven pin sockets were next. Both five and seven pin sockets are made new in ceramic form because military and aeronautical ground equipment using 807 and 1625 tubes and similar are still supported. Six pin sockets are not as far as I know in current production but are still cheaply available as old stock.

Octal Developed

The next stage of tube development was the introduction of metal envelope tubes and the octal base. It had eight pins equally distributed around a circle of established diameter and was oriented, or made to put in the socket only one way, by a central molded nonconductive pin with a male ridge or nub which fit into a recess in the sidewall of the center hole. Large numbers of tubes were introduced in this new configuration and the metal envelope was touted as the highest and most sublime development in the manufacture of receiving tubes.

The metal envelope was soon replaced by a glass one for various reasons, but the octal socket stayed. The octal socket was touted as replacing all previous socket systems and before WWII it largely had done so. It is the most common tube socket made today because it is used for industrial relays and control electronics as well as connecting cables, ovenized crystal oscillator time bases, and military ordnance and oil field blasting applications as well as for tubes.

Loktal Sockets

One variation tried and soon abandoned was the Loktal. Octal tubes were not secured and like previous socket systems since the earliest UX, the tubes could come out of the socket if the contacts became loose, The Loktal used a similar pattern as the octal, eight pins, but they were thinner pins and the center locating pin had a circular groove which locked in to a snap fitting in the socket. The Loktal faded away and though a few Loktal types were used after WWII it was largely extinct by 1955. Loktal sockets are not made any more but show up at ham-fests often enough for anyone wanting to homebrew something with them.

Other Octal Sockets

Other variations on the octal to be aware of are the "eleven pin octal", which seems an oxymoron since 'octal' means 'pertaining to the number eight'. Audio applications include the connecting cables on Hammond organs and Leslie speaker cabinets: the eleven pin octal is also used on Collins, Heath and Drake ham gear, Heathkit power supplies and elsewhere for cables. There are also octal connectors with multiple female grooves in the locating pin center socket designed so that male octal connectors can only fit a specific socket. This is of interest because the sockets come up surplus and will work for tubes, but the tubes could plug in one of two orientations, one of which would be disastrous. (Photoflash studio power units from the 50s and 60s used these a lot-B)

Finally, there is a British Octal that looks identical to the normal (US) one but has a larger diameter of pin circle and center pin and will not fit a regular octal socket. It is used on one of the tube types called out in the original Williamson Amplifier as published in Wireless World, but otherwise is only seen in surplus British and British Commonwealth military radios and tube testers and in one British Decola radiogram of which surely only one exists in the United States. Since that one belongs to the writer's wife-a former WREN who emigrated to marry said writer-it will be left to the imagination how that was brought to this writer's attention. It is no longer common even in the UK, according to writer Morgan Jones.

Miniature Types

With the evolution of VHF and UHF communications, FM radio, and television, the all glass miniature types of tubes became popular. Their smaller size made higher frequency use feasible and the saving in space resulted in smaller and lighter-and cheaper-equipment. Miniature tubes became totally dominant in small signal and small power and rectifier applications by 1955.

The two common sizes are the seven and nine pin (Noval) standard miniature. The seven pin was used for diodes and triodes in UHF and detector applications and many other small signal purposes. The nine pin was more common for dual triodes, pentodes, and small power tubes and small power rectifiers. Both were made by the billions and used everywhere but today the nine pin is vastly more common. This is what common tubes like the 12AX7 and EL84 use and is certainly widely made today. I do not know whether the seven pin socket is still made but is still available in modest quantity.

Two rare but extant variants of the nine pin are a ten and thirteen pin socket which has one or four center pins. These can be ignored and the socket used as a standard nine in with normal tubes, but obviously not the other way around. The ten is used for one or two types used in TVs: the thirteen is used for certain Nixie displays with alphanumeric odd or Cyrillic characters.

Novar and Magnoval Sockets

These two are almost but not quite the same and plugging the wrong one in the wrong socket will damage one or the other. Novar sockets are used on some larger 9 pin tubes such as the 7868. They look like regular nine pin tubes but are larger. Magnoval tubes are a similar, usually European base but the circle is slightly larger and the pins are much fatter. Putting a Magnoval tube in a Novar socket will permanently damage the socket and over time may damage the tube as well. The reverse will cause long term damage as well.

Complicating matters is that some Russian Novar types have excessively fat pins, and also there were a few sockets that were designed to work with either tube, but were not common. They were bulkier and more expensive.

Compactron Socket

The Compactron was a 12 pin envelope and socket system developed by GE to accommodate double pentodes, triple triodes and other large scale integrated groupings of vacuum tubes. This was late in the career of receiving tubes and was designed to keep the tube designs semi-competitive with solid state. It failed, but Compactrons are still occasionally used as sweep tubes in RF linear amplifiers. There is only one Compactron socket and that is what fits it. Had GE management approved a second generation of Compactrons it is unknown what they would have done.

Nuvistor Sockets

The Nuvistor was RCA's attempt to stave off solid state as well, but was a very small tube with a tiny base much like that of certain transistors and early ICs. The standard Nuvistor socket was a five pin, but a seven pin also is known to exist and there may be others. Nuvistors were used in avionics and Tektronix oscilloscopes and in TV tuners primarily on the UHF side. Audio applications were rare because they were often microphonic.

CRT Sockets

Although some CRTs use normal octal sockets, most used one of several 12, 14 or more pin sockets mostly peculiar to CRTs. These sockets were occasionally used for other things and should be recognized as such. Some console stereos used them as an interconnect between the RF head/phono pre-amp and the power supply/power amplifier chassis. Some photo-multipliers and camera tubes used them too.

Transmitting Tube Sockets

Small transmitting tubes may use four, five, seven pin or octal sockets. Larger triodes such as the 211 or 845 have a round four pin socket. Smaller VHF tubes may have a larger base seven pin socket, Septar, such as that on the 829B or 832, which is also used on the Russian 6S33 (which resembles 6C33 in Latin script) regulator tube discovered when Belenko defected in the MiG-25. The 813 is a common beam power pentode with a "Giant" seven pin base, larger than the Septar. (The Altec 260B is an audio application). There are literally dozens of other sockets for larger tubes, each socket accommodating one or two types and some types like the venerable 4CX250 series made in different versions with different sockets. Tubes made for forced air cooling have sockets designed as an integral part of the air cooling system, and ones for over 250-400 MHZ usually have coaxial ones.

Foreign Receiving Sockets

The Germans, the Dutch, and the British all had lines of tube sockets incompatible with each other and with American designs, although after WWII this decreased in importance and at the end of tube production for consumer use most of these proprietary sockets were long since replaced. I cannot provide comprehensive information on these but know some basics. It is generally agreed that the reason for this was to prevent foreign competition undercutting their markets, rather than strictly technical ones.

The British had as mentioned before a larger octal socket, the Mazda Octal. They also used the US or, as they called it, International Octal. While at least a dozen British proprietary sockets exist, this and the four and five pin bases used on early power tubes like the PX4 are all you will probably ever see. There is also a unique square socket used with the DA100 and other British directly heated triode power tubes, which will remind Americans of the old (before modular) four pin square telephone plug used in Bell Telephone residential use.

Many German sockets were used before, during and somewhat after WWII and I will defer to others any comprehensive description. Some of these actually enveloped the tube which was a small acorn type inserted envelope down into the socket, and this was copied by Warsaw Pact countries after WWII fairly extensively.

Philips used a peculiar lock-in base molded in the glass envelope in many small signal types well after WWII. These were superseded by the regular nine pin miniatures.

Types peculiar to Warsaw Pact countries (i.e., the Soviet Union and its satellite states before the breakup of the Soviet Union) are beyond my field of scope. I do know that the majority of their receiving tubes use Western sockets, with transmitting and special purpose types often having unusual basing.