Editing Tube socket (section)

==Loctal==
[[File:Heksoda i trioda UCH21.jpeg|thumb|upright|A loctal-base tube, Polish Telam UCH21 next to a wooden match for size comparison]]
A variant of the octal base, the B8G '''loctal base''' or ''lock-in'' base (sometimes spelled "loktal"&nbsp;— trademarked by Sylvania), was developed by [[Sylvania Electric Products|Sylvania]] for ruggedized applications such as automobile radios. Along with B8B (a British designation out of date by 1958), these eight-pin locking bases are almost identical and the names usually taken as interchangeable (although there are some minor differences in specifications, such as spigot material and spigot taper, etc.).<ref>{{cite book|author1=Staff of 'Wireless World'|title=Radio Valve Data|date=1958|publisher=Iliffe $ Sons Ltd|location=London|page=87|edition=Sixth|chapter=Explanation of Valve-Base Connections}}</ref> The pin geometry was the same as for octal, but the pins were thinner (although they will fit into a standard octal socket, they wobble and do not make good contact), the base shell was made of aluminium, and the center hole had an electrical contact that also mechanically locked (hence "loctal") the tube in place. Loctal tubes were only used widely by a few equipment manufacturers, most notably [[Philco]], which used the tubes in many table radios. Loctal tubes have a small indexing mark on the side of the base skirt; they do not release easily from their sockets unless pushed from that side. Because the pins are actually the [[Fernico]] or [[Cunife]] lead-out wires from the tube, they are prone to intermittent connections caused by the build-up of electrolytic corrosion products due to the pin being of a different metallic composition to the socket contact.

The loctal tube's structure was supported directly by the connecting pins passing through the glass "button" base. Octal tube structures were supported on a glass "pinch", formed by heating the bottom of the envelope to fusing temperature, then squeezing the pinch closed. Sealing the pinch embedded the connecting wires in the pinch's glass and gave a vacuum-tight seal. The connecting wires then passed through the hollow base pins, where they were soldered to make permanent connections.

Loctal tubes had shorter connecting lengths between the socket pins and the internal elements than did their octal counterparts. This allowed them to operate at higher frequencies than octal tubes. The advent of miniature "all-glass" seven- and nine-pin tubes overtook both octals and loctals, so the loctal's higher-frequency potential was never fully exploited.

Loctal tube type numbers in the USA typically begin with "7" (for 6.3-volt types) or "14" for 12.6-volt types. This was fudged by specifying the heater voltage as ''nominally'' 7 or 14 volts so that the tube nomenclature fitted.<ref>{{cite web|title=Sylvania Type 7A8|url=http://frank.pocnet.net/sheets/108/7/7A8.pdf|access-date=20 July 2013}}</ref> Battery types (mostly 1.4-volt) are coded "1Lxn", where ''x'' is a letter and "n" a number, such as "1LA4". Russian loctals ''end'' in L, e.g. 6J1L. European designations are ambiguous; all B8G loctals have numbers either in the range:
* 20–29, (such as EBL21, ECH21, EF22) except for early tubes in the series: DAC21, DBC21, DCH21, DF21, DF22, DL21, DLL21, DM21 which have either B9G or octal bases, the change to Sylvania's locktal standard coming in 1942<ref>{{cite web|title=DAC21|url=http://www.radiomuseum.org/tubes/tube_dac21.html|access-date=25 August 2012}}</ref>  
* or 50–59 (special bases, including the European 9-pin lock-in base), but other types are in the same range (e.g. while EF51 is B8G loctal, the EF55 is 9-pin loctal, B9G, and the EL51 has a side-contact P8A base).

===Other loctals===
* Nine-pin loctal bases, B9G, include the 1938 Philips [[EF50]], EL60 and some type numbers in the European 20–29 and 50–59 range;
* There is a different "loctal Lorenz" in the [[Mullard–Philips tube designation]] <!--COMMENT (B8D, given numbers in the 70–79 range?)-->.