Editing Tube socket (section)

==Miniature tubes==
[[File:12AU7.jpg|thumb|left|A pair of 12AU7As (ECC82) showing both triodes.]]
Efforts to introduce small tubes into the marketplace date from the 1920s, when experimenters and hobbyists made radios with so-called '''peanut tubes'''<ref>[http://www.stonevintageradio.com/images/573.jpg Photo of 1920s era peanut tube.]</ref> like the Peanut 215 mentioned above. Because of the primitive manufacturing techniques of the time, these tubes were too unreliable for commercial use.

RCA announced  new miniature tubes in [[Electronics (magazine)|''Electronics'']] magazine, which proved reliable. The first ones, such as the 6J6 ECC91 [[Very high frequency|VHF]] dual triode, were introduced in 1939. The bases commonly referred to as "miniature" are the seven-pin B7G type, and the slightly later nine-pin B9A (Noval). The pins are arranged evenly in a circle of eight or ten evenly spaced positions, with one pin omitted; this allows the tube to be inserted in only one orientation. Keying by omitting a pin is also used in 8- (subminiature), 10-, and 12-pin ([[Compactron]]) tubes (a variant 10-pin form, "Noval+1", is basically a nine-pin socket with an added center contact).

As with loctal tubes, the pins of miniature tube are stiff wires protruding through the bottom of the glass envelope which plug directly into the socket. However, unlike all their predecessors, miniature tubes are not fitted with separate bases; the base is an integral part of the glass envelope. The pinched-off air evacuation nub is at the top of the tube, giving it its distinctive appearance. More than one functional section can be included in a single envelope; a dual triode configuration is particularly common. Seven- and nine-pin tubes were common, though miniature tubes with more pins, such as the Compactron series, were later introduced, and could fit up to three amplifying elements. Some miniature tube sockets had a skirt that mated with a cylindrical metal electrostatic shield that surrounded the tube, fitted with a spring to hold the tube in place if the equipment was subject to vibration. Sometimes the shield was also fitted with thermal contacts to transfer heat from the glass envelope to the shield and act as a [[heat sink]], which was considered to improve tube life in higher power applications.

Electrolytic effects from the differing metal alloys used for the miniature tube pins (usually [[Cunife]] or [[Fernico]]) and the tube base could cause intermittent contact due to local corrosion, especially in relatively low current tubes, such as were used in battery-operated radio sets. Malfunctioning equipment with miniature tubes can sometimes be brought back to life by removing and reinserting the tubes, disturbing the insulating layer of corrosion.

Miniature tubes were widely manufactured for military use during World War II,<ref name=sixj6>[http://www.r-type.org/exhib/aaa0399.htm The National Valve Museum: 6J6]</ref> and also used in consumer equipment. The Sonora Radio and Television Corporation produced the first radio using these miniature tubes, the "Candid", in April 1940.<ref name=schiffer>{{cite book|last=Schiffer|first=Michael Brian|title=The Portable Radio in American Life|year=1992|publisher=University of Arizona Press|isbn=978-0816512843|pages=123–125}}</ref> In June 1940 RCA released its battery-operated '''Model BP-10''', the first [[superheterodyne receiver]] small enough to fit in a handbag or coat pocket.<ref>[http://www.nostalgiaair.org/PagesByModel/428/M0015428.pdf Schematic of RCA Model BP-10]</ref><ref>[http://vintage-electronics.com/photos/1183.JPG Photo of RCA Model BP-10]</ref>  This model had the following tube lineup:  '''1R5'''&nbsp;— [[pentagrid converter]]; '''1T4'''&nbsp;— [[Intermediate-Frequency_(IF)_amplifier|I.F. amplifier]];  '''1S5'''&nbsp;— [[Detector_(radio)|Detector]]/AVC/AF Amplifier;  '''1S4'''&nbsp;— Audio Output. The BP-10 proved so popular that Zenith, Motorola, Emerson, and other radio manufacturers produced similar pocket radios based on RCA's miniature tubes.<ref name="schiffer" /> Several of these pocket radios were introduced in 1941 and sold until the suspension of radio production in April 1942 for the duration of World War II.<ref>{{cite journal|title=Miniature Radio Tubes|journal=Radio Age|date=April 1945|pages=19|url=http://www.vacuumtubeera.net/RadioAge-1945-04.pdf|access-date=20 July 2013}}</ref>

After the war miniature tubes continued to be manufactured for civilian use, regardless of any technical advantage, as they were cheaper than octals and loctals.<ref name=sixj6/>

{{anchors|Miniature seven-pin base|Miniature 7-Pin}}
=== Miniature seven-pin base ===
The '''B7G''' (or "'''small-button'''" or "'''heptal'''") seven-pin miniature tubes are smaller than Noval, with seven pins arranged at 45-degree spacing in a 9.53&nbsp;mm (3/8th inch) diameter arc, the "missing" pin position being used to position the tube in its socket (unlike octal, loctal and rimlock sockets). Examples include the 6AQ5/EL90 and 6BE6/EK90. European tubes of this type have numbers 90-99, 100-109, 190-199, 900-999. A few in the  100-109 series have unusual, non-B7G bases, ''e.g.'', Wehrmacht base.

{{anchors|Noval|Noval base|Miniature nine-pin base|Miniature 9-Pin}}
=== Noval base ===
The nine-pin miniature '''Noval''' B9A base, sometimes called button 9-pin, B9-1, offered a useful reduction in physical size compared to previous common types, such as octal (especially important in TV receivers where space was limited), while also providing a sufficient number of connections (unlike B7G) to allow effectively unrestricted access to all the electrodes, even of relatively complex tubes such as double triodes and triode-hexodes. It could also provide multiple connections to an electrode of a simpler device where useful, as in the four connections to the grid of a conventional grounded-grid UHF triode, ''e.g.'', 6AM4, to minimise the deleterious effects of lead inductance on the high-frequency performance.

This base type was used by many of the [[United States]] and most of the European tubes, ''e.g.'', [[12AX7]]-ECC83, [[EF86]] and [[EL84]], produced commercially towards the end of the era before [[transistor]]s largely displaced their use.

The IEC 67-I-12a specification calls for a 36-degree angle between the nine pins of 1.016&nbsp;mm thickness, in an arc of diameter 11.89&nbsp;mm.

European tubes of this type have numbers 80-89, 180-189, 280-289, 800-899, 8000-8999.

=== Duodecar base ===
The '''Duodecar''' B12C base (IEC 67-I-17a) has 12 pins in a 19.1&nbsp;mm diameter circle and dates from 1961. It was also called the [[Compactron]] T-9 construction/E12-70 base<ref>Sylvania Receiving Tubes Technical Manual, 14th Edition</ref> It is generally similar in form to a Noval socket, but larger. In the center is a clearance hole for a tube evacuation pip, which is typically on the bottom of a Compactron tube. <!-- also CRTs, fairly sure. Regards, user:nikevich --> (It should not be confused with the similar-sounding but differently sized '''Duodecal''' B12A base.)

=== Rimlock base ===
The '''Rimlock''' (B8A) base is an eight-pin design with a pin circle diameter close to Noval, and uses a nub on the side of the envelope to engage with a guide and retaining spring in the socket wall. This provides pin registration (since the pins are equi-spaced) and also a fair degree of retention. Early tubes with this base type typically had a metal skirt around the lower ~15mm of the envelope to match the socket wall, and this offered a degree of built-in screening, but these were fairly soon replaced by "skirtless" versions, which had a characteristic widening in the glass to compensate physically for the absence of the skirt. In the European naming scheme, rimlock tubes are numbered in the ranges 40-49, 110-119 (with exceptions), and 400-499, ''e.g.'', EF40. Although virtually unknown elsewhere, this was a very common base type in European radios of the late 1940s through the 1950s, but was eventually displaced by the ubiquitous B7G and Noval (B9A) base types.