Transistors and Diodes

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Western Electric 1729

Shortly after the invention of the transistor at Bell Laboratories in 1947, the engineers at Bell began the process of converting the transistor from a rickety science experiment into a useful and manufacturable device. In 1949 Bell began the production of two transistor part numbers derived from it's original 'Type A' production prototypes; the Western Electric 1729 linear transistor and 1698 switching transistor. These were point contact devices; a pair of spring loaded contacts were pressed against a crystal of germanium to form the semiconductor junction. Point contact transistors were an unreliable technology that required manual positioning of the contacts in order to work correctly, and all of the devices built around the original Type A cartridge package included a pair of round windows to allow for manual adjustment of the contact position. The window was covered by a sliding plastic tube when not in use. The tubular package of the 1729 and its relations was designed to be used with a special socket; a locking tab would hold the transistor in place once it was inserted. The 1729 was produced under several different part numbers over its lifespan, starting with the M1729 in 1949 and ending with the JEDEC 2N25 assignment in the mid 1950s. The example shown here is an A1729 and was produced in March 1954.

The original Type A transistor differed from the more usable 1729 in several ways, most notably in having its thick leads pre-bent at a right angle to the vertical axis that prevented a socket from being made for the device. The original Type A was only produced in small quantities to be sent to other companies for testing and experimentation. Point contact transistors in general were a short lived technology; when the more robust grown junction transistor arrived on the market in 1952, point contact devices were rendered obsolete. Outside of early hearing aids and a few telephone switching systems, point contact transistors saw almost no commercial use.


Western Electric 1729 Point Contact Transistor (M1729, A1729, 2N25)
Raytheon CK718 & CK722

Released in 1953, the blue painted Raytheon CK722 PNP transistor is quite possibly the most famous and beloved transistor ever made. Initially made in a clear plastic painted package, the CK722 was part of a family of parts originally derived from the CK718 hearing aid transistor. Early transistor production was a slapdash affair at best, and many of the CK718's that Raytheon produced did not meet the advertised specifications. These low-bin parts were packaged under a different part number, CK722, and sold as low performance devices specifically for the hobby market. As a result, an entire generation of electronics enthusiasts cut their teeth on blue painted CK722 transistors. The CK722 became so iconic that Raytheon began to paint their other semiconductors in the same shade of blue to capitalize on the popularity of the device.


Raytheon CK718 & CK722 Transistors
Raytheon CK782

The CK782, made by Raytheon, is a germanium PNP transistor intended for use in early hearing aids. First released sometime around 1955, the early CK782's make use of Raytheon's iconic blue paint job, popularized by the hobbyist friendly CK722 shown above. The CK782 is quite tiny for a metal can transistor, rivaling the size of later devices in TO-92 plastic enclosures.


Raytheon CK782 Transistor
General Electric 2N107

Bolstered by the success of Raytheon's popular CK722, General Electric decided to sell their own hobbyist-grade transistor, the 2N107. First released in 1955, the 2N107 was initially produced by re-labeling rejected 2N43 transistors and selling them at a steep 80% discount. Despite this humble origin, the 2N107 still provided good performance for homebrew electronics, and the transistor enjoyed wide popularity and a long product lifetime. 2N107's were still being produced well into 1970's, with later versions being manufactured to spec and housed in standard TO-5 metal can enclosures. Early 2N107's are encased in hermetically sealed 'top hat' enclosures, which provided improved reliability when compared to the resin-encased CK722 transistors they were designed to compete with.


General Electric 2N107 Transistor
Sprague 2N128

The 2N128 and 2N129, initially released by Philco in 1953, were the first commercially produced surface barrier transistors. Surface barrier transistors make use of an improved manufacturing process, in which jets of indium sulfide were used to erode a germanium die down to a thickness of only a few thousandths of an inch. Indium was then electroplated to each side of the die, resulting in a junction with superior high frequency response to the point contact and alloy junction transistors available at the time. The 2N128 contains a vertically mounted surface barrier die bonded to a three pin base, which is packaged in an pill-shaped TO-24 aluminum enclosure. The example shown here is a second-sourced variant produced by Sprague.

Philco surface barrier transistors were a commercial success, and saw use in a number of historic devices including the UNIVAC LARC supercomputer, the AN/GSQ-33 ground guidance computer for the Atlas ICBM, and the Athena ground guidance computer for the Titan 1 ICBM. Philco surface barrier transistors were also used in Explorer 1, the first satellite launched into orbit by the United States and the third in the world, following the successful launch of Sputnik 1 and Sputnik 2 the prior year by the Soviet Union.


Sprague 2N128 Transistor
Teledyne TR1002 Fetron

Devices included in this entry:

Teledyne TR1002 (7 pin hermetic package, pictured in thumbnail)
Western Electric KS 21073 (7 pin hermetic package)

During the twilight of the electron tube era, many companies produced solid state tube replacements; semiconductor devices designed to mimic the shape and function of an electron tube. One such device was the Fetron, a metal can semiconductor that resembles a TO-5 transistor scaled up to comic proportions. Believed to have been originally produced by Western Electric, Fetrons were intended to replace the large number of glass electron tubes used in legacy telephone switching systems. The example shown here, a TR1002 solid state diode produced by Teledyne, is a 7 pin device intended to be a drop in replacement for a 6AL5 electron tube. The inside of the can is mostly empty space intended to make the device feel more 'tube-like', a ceramic wafer hybrid microcircuit is preformed to the bottom of the can and attached to the leads with bond wire. A plastic spacer attached to the base prevents the tube's metal case from shorting out when pressed against older legacy tube sockets.

Fetrons are probably best known for their use by Heathkit, which marketed a solid state conversion kit for their line of tube-based voltmeters. This kit could convert Heathkit and competitor VTVM's over to solid state components, and included a TR1002 diode as well as a 9 pin TR1119 triode.


Teledyne TR1002 Fetron Solid State Tube Replacement (TR1002 & KS 21073)
Sylvania 2N35

The Sylvania 2N35 is an early consumer-grade germanium transistor, notable for its NPN construction at a time when most of the available devices were of PNP construction. Released in 1953, the 2N35 was a competitor to the popular Raytheon CK722. Like many early transistors, the 2N35 is packaged in a small elliptical metal can, which can mate to common transistor sockets of the era.


Sylvania 2N35 Transistor
General Electric 2N43

The 2N43, along with the 2N44 and 2N45, were General Electric's first commercially produced alloy junction transistors. First produced in 1953, the 2N43 used a vacuum-sealed glass and metal package designed by Conrad Zierdt, a General Electric production engineer. This packaging, which abandoned the failure-prone epoxy and potting compounds of other early transistors, significantly lowered electrical variation between devices. A variant of this transistor, the 2N43A, was the first transistor to be qualified for use by the USAF.


General Electric 2N43 Transistor (2N43A)
Raytheon CK784

In the early days of the transistor era, Raytheon produced a number of small audio frequency devices for use in the hearing aid market. The Raytheon CK784 is one such device; a tiny metal can PNP transistor intended for use in audio amplifiers. The CK784 is approximately half the size of Raytheon's popular hobbyist-friendly CK722 transistor, and is small enough to encroach on the size of a modern TO-92 device. Raytheon's iconic blue paint, also popularized by the CK722, is present and accounted for.


Raytheon CK784 Transistor
Siemens TF65

The TF65 is a germanium junction transistor that introduced in 1957. This transistor was made in both a silver and black cased version; the black version is shown here. This model of transistor is best known for it's use inside Kundo's line of electromagnetic pendulum clocks, which make use of the transistor in the pendulum drive circuit. The TF65 is a common point of failure in these clocks, requiring replacement with a more readily available germanium part number, the AC125 being the most common choice.

Siemens TF65 Transistor
Mullard ORP61

The ORP61, manufactured by Mullard, is a cadmium sulfide photocell in a tiny tubular package. The clear case of this device mimics the shape of many earlier transistors manufactured in Europe and Great Britain, a fact which causes many collectors to mistakenly identify this part as a diode or transistor. The strange internal construction of the ORP61 does little to help in identification; this part lacks the typical serpentine pattern of the average photo-resistor, instead a translucent block is bonded across two leads at the head of the device. The ORP61 has a nominal resistance of 60kOhms and a maximum power rating of 70 mW at 350 volts DC.

Mullard ORP61 Photocell
Fairchild FPA 700

The Fairchild FPA700 is a very early phototransisor array, which was first produced in the late 1960s. Intended for use in paper-tape reading machines, the FPA 700 is constructed out of nine NPN phototransistor dies packaged in a crude plastic encapsulation. Each phototransistor is protected by a layer of transparent resin and is wired to a dedicated pair of gold leads. The FPA 700 is rated for a maximum of 20 volts and 25ma of current per phototransistor cell. The example shown here has a date code of 1969.


Fairchild FPA 700 Phototransistor Array
CBS Hytron 2N158

The 2N158 is a large PNP germanium power transistor that was introduced in 1956. Originally produced by CBS Hytron, this transistor saw wide use by the military and continued to be produced by Raytheon well into the 1960s. The 2N158's large cylindrical package is designed specifically for heat dissipation; the top of the transistor package is a solid ingot of metal with a threaded hole for use with an external heatsink. This part went through several revisions, with the earliest versions using a white painted metal enclosure before switching to the black transistor package shown here. By the end of the 2N158's production run, examples were being manufactured in unpainted metal cases with a large central flange around the circumstance of the transistor package. The 2N158 is rated for a maximum of 20 watts at an operating voltage of 60 volts.


CBS Hytron 2N158 Transistor
Motorola 2N174

The 2N174 is an early PNP germanium power transistor. Manufactured by a number of companies including Motorola, Delco, and Tung-Sol, the 2N174 is encased in a large TO-36 'doorknob' package with gold coating and a threaded heatsink stud. The primitive alloy junction transistor die used in this device will cease to function if exposed to air; for this reason the 2N174 includes an evacuation nipple on its underside for removal of air from the transistor package. The earliest 2N174's were produced by Delco in 1956 for use in automobile radios. These early Delco devices were packaged in tall TO-36 metal enclosures with a paper label on top to denote the JEDEC device part number. Tung-Sol and Motorola soon became second source suppliers for the 2N174, with each manufacturer using their own distinctive package style for the part. Tung-Sol 2N174's are painted with an easily recognized light blue coating, while Motorola opted for the gold and black package shown here. The 2N174 is rated for a maximum of 15 amps at its maximum output voltage of 80 volts DC.


Motorola 2N174 Transistor
Raytheon CK2000

If a steampunk fetishist was tasked with building an old-timey analog optoisolator, a raysistor might be the result. Raysistors are primitive optical isolation components that contain an incandescent bulb and a CDS photoresistor closely coupled in a blob of clear epoxy. The example shown here, a CK2000 manufactured by Raytheon, has had it's metal cover removed so the internal structure can be seen. Raysistors have one immediately obvious disadvantage over optoisolators... incandescent lamps can and do burn out. For this reason the CK2000 is designed to be a user replaceable part, and mates with a special four-pin socket that was provided in the same packaging.

Raytheon also produced much longer lasting raysistors that utilized a neon bulb instead of an incandescent lamp as the light source. This eliminated the threat of a burned out lamp filament, but resulted in a part with much more limited analog capabilities.


Raytheon CK2000 Raysistor
Western Electric 2N559

The Western Electric 2N559 is an early germanium PNP transistor that was likely first produced in 1959. Noteworthy for it's use in the US Nike Zeus missile defense system, the 2N559 was first produced in a gold plated metal can enclosure with an attached evacuation pip. After 1961, Western Electric eliminated the pip and switched to the use of a barium hydroxide alloy sponge, which was sealed within the transistor package to absorb any latent gasses. These later manufacture 2N559's are packaged in a black painted metal can, similar in size to a standard TO-18 transistor package. The 2N559 was manufactured at Western Electric's Laureldale plant.


Western Electric 2N559 Transistor
US Army MILES Photodiode

This large photodiode has a more interesting pedigree than one would expect... it was built to take part in the planet's most sophisticated game of laser tag. The Multiple Integrated Laser Engagement System, or MILES, was a program started in 1978 by the United States Army with the goal of using lasers for simulated combat exercises. Soldiers would wear special attachments on their helmets that were ringed with these photodiodes, which could detect bursts of laser light from modules that could be attached to the barrel of an M16 rifle. As would be expected from the US Army, this photodiode looks like something the Klingon Empire would build if it developed a sudden interest in optoelectronics. The large diode die is encased in a heavy three piece metal enclosure with a glass cavity window. The cavity window is traced with a fine grid of wires, most likely to provide an extra layer of electromagnetic shielding to the semiconductor within. In operation the entire diode would be covered with a dark plastic dome, which would filter out ambient light and prevent false positives. We have been unable to date this part; the MILES system underwent many revisions over the years and is still in use today.

Early MILES battle simulations were allegedly fraught with the types of problems familiar to anyone who played laser tag in the 1980's, including 'zombie' soldiers, who could continue to fight after being killed. By the mid 1980s a loud alarm was added to the sensor system to prevent this, which could only be silenced by inserting a key into the control box for the sensors. The same key was also required to activate the laser on the soldier's rifle; when a soldier was 'killed', the key would have to be removed from the rifle to deactivate the buzzer on the sensor control unit, rendering the rifle inoperative in the process.


US Army MILES Photodiode
Philco 1N82

The 1N82 is a mid-1950s era germanium diode intended as a low loss mixer for use in television receivers. The 1N82 has a classic 'cat whisker' point contact, which can be seen pressing against the diode's square germanium crystal through the glass housing. Unlike some earlier devices, no provision has been included for manual adjustment of the point contact's position after installation of the diode in it's target system.


Philco 1N82 Transistor
Burroughs B5000 Diode Logic Module

This early diode module is a plug-in logic element from a Burroughs B5000 mainframe. The B5000, which was released in 1961, was the first computer produced in-house by the Burroughs corporation. The B5000 was assembled from large numbers of modules such as this, which contains 8 diodes mounted in a diallyl pthalate carrier. An array of pins along the edge of the module connect it to the rest of the computer system.

The Burroughs B5000 also contained larger plugin 'cordwood' modules, which contained transistors and passive components wired between two parallel circuit cards. Each module had a pin grid array and a metal handle on opposing faces, for easy removal.


Burroughs B5000 Diode Logic Module
United Detector Technology UDT PIN-10D

This is a PIN-10D planar silicon photodiode, a monstrous solid state photon collector produced by the United Detector Technology. The active area of this device is over 11mm in diameter, and the silicon die is packaged in a large metal enclosure that would make any standard TO-5 photodiode feel positively emasculated. The PIN-10D does not have pins; instead a standard BNC socket connector has been incorporated directly into the device's package.


United Detector Technology UDT PIN-10D Planar Silicon Photodiode
Honeywell H5

The Honeywell H5 is an early power transistor which was released in 1956. The H5 is a germanium PNP device with a power rating of 10 watts, and is the first Honeywell power transistor to use hook lugs instead of flying leads. Honeywell originally developed this series of transistors for use in aircraft fuel systems; some versions had power dissipation ratings in excess of 50 watts.


Honeywell H5 Transistor
Honeywell H10

The Honeywell H10, first released in 1957, is a successor to the 1965-era H5 power transistor. The H10 is a large metal-can device with hook leads and a threaded lug for heatsink or chassis mounting. This transistor has a power rating of 15 amps, and was packaged in a case almost twice the diameter of the earlier H5. The example shown here is a undefined later variant, marked with the part number H10A1XOC.


Honeywell H10 Transistor
General Electric 2N188

The 2N188 is a relatively unremarkable early PNP transistor manufactured by General Electric. The 2N188 was intended to be used as a medium power audio frequency amplifier, and has fairly linear gain and output. This transistor is packaged in a top-hat package; earlier versions included a top nipple for evacuation, which was dropped in later revisions.

General Electric 2N188 Transistor

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