![]() ![]() The original OCP71 germanium photo-transistor (filled with clear gunge) cost an obscene amount of hard earned cash - twelve shillings and six pence whereas the OC71 typically cost four shillings and six pence (still a lot when pocket money was earned rather than just given). The OCP71 was a Photo Transistor being a clear enveloped version of OC71 germanium transistor.John Paine, London UK, 19th of August 2015 This lacquer was very flammable and was applied by a rotary machine housed in a sealed flameproof room which in the event of a fire could be automatically flooded with CO2 - this made one quite nervous when it was necessary to work on this paint machine as there was only 10 seconds to exit the room before drowning in CO2. The Black finish was a cellulose dope onto which the Type Number could be transfer printed. To give mechanical protection to the delicate wire connections of the Indium pellets which formed the transistor Collector and Emitter junctions the bare assembly could be dipped into blue Silicon "Bouncing" Putty before being placed into the alundum filled glass bulb which had been centrifuged to expelled any air pockets which might reduce heat conduction. To improve the heat conduction a mixture of silicon oil and aluminium oxide was used - this also improved the performance by reducing effects of light reaching the sensitive transistor junction. The so called "Gunge" in the transistor encapsulation is Silicon Grease which provides some heat conduction from the transistor junctions. ![]() Tony Barker, Petersfield, Hampshire, 25th of February 2022 With much high frequency boost in the receiver I got a 7kHz frequency range and listened to Mozart along the beam, over 100 metres. I used an OCP71 (or it might just have been a scraped OC71)in a minor project at university as the receiver of a modulated light beam using a 24V 1W filament lamp as the transmitter, feeding an audio signal from a portable radio plus a DC current just enough to make the lamp glow orange.Mullard later changed the jelly surrounding the germanium element inside probably to stop this being possible. As these were more expensive than ordinary transistors, it was found that an OC71 transistor (much cheaper) was also sensitive to light if the paint was remove from its surface. Mullard light sensitive transistor known as a 'Phototransistor'. Home: Semiconductors: MULLARD OCP71 PHOTO DIODE, 1960's ![]()
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