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OC71 Transistor Data

Key transistor data for the OC71 PNP audio germanium transistor including key electrical parameters, pinout, package type and many other key transistor datasheet details.

The OC71 was a general purpose audio low power amplifier housed in a black painted glass encapsulation to provide rugged protection of the device.

Image of an old OC71 transistor - this type was introduced by Mullard in Britain in 1954, but production continued well beyond this date into the 1960s — Old OC71 bipolar transistor

Key details and performance parameters for the OC71 transistor.

nnn transistor datasheet parameters & data
Parameters	Details
Transistor type	PNP germanium audio transistor
Package type
V_CBO max (V)	-20
V_CEO max (V)	-20
V_EBOmax (V)	10
I_C max (mA)	10
T_J Max °C	80
P_TOT mW	125
f_T min (MHz)	0.3
C_OB	30
h_fe	30 min
I_C for h_fe	5mA
Similar / equivalents

Outline:

Pinout:

Explanation of transistor parameters

Parameter	Explanation
V_CBO Max	Maximum collector-base voltage with emitter open circuit .
V_CEO Max	Maximum collector-emitter voltage with base open circuit.
V_EBO Max	Maximum emitter-base voltage with collector open circuit.
V_CEsat (included where applicable)	The voltage drop across the collector-emitter when the transistor is fully saturated (acting as a closed switch).
I_C Max	Maximum collector current.

Parameter	Explanation
T_J	Maximum junction temperature.
P_TOT Max	Maximum device dissipation normally in free air at 25°C unless other conditions indicated.
f_T Min	Minimum cutoff frequency at which the current gain in a common emitter circuit falls to unity.
C_OB Max	Maximum collector capacitane, normally measured with emitter open circuit.
h_FE	DC current gain for H_FE at I_C. [Note hfe is the small signal gain and although this may be slightly different, the transistor current gain will vary considerably from ne transistor to the next of the same type.]
P_TOT Max	Maximum device dissipation normally in free air at 25°C unless other conditions indicated.

These are the main transistor parameters that have been included in our list. There are others, but these help quantify the main elements of the performance of the transistor.

Read more about . . . . Transistor Data-sheet Specifications & Parameters.

Please note, that the data given is the best estimate we can give within a tabulated summary of this nature. Parameters also vary between manufacturers. Electronics Notes cannot accept any responsibility for errors, inaccuracies, etc, although we do endevaour to ensure the data is as accurate as possible.

Notes and supplementary information

• Timeline

The OC71 was one of the first transistors available for both industrial and home experimentation. Its number is engrained in the minds of many electronics and radio enthusiasts of te say.

The device was a general purpose audio transistor which was launched in 1954 by the Phillips company which also owned the British company Mullard.

The OC71 was manufactured in large quantities and devices bearing the Philips and the Mulard names can still be seen in many component boxes and in many radios, etc.

In fact te OC71 was a replacement for an earlier transistor, the OC11 which had been developed as a general purpose audio transistor.

• OCP71 phototransistor& OC71

The OC71 was housed in a glass encapsulation. This was painted black to prevent it being affected by light. A phototransistor - the OCP71 in some respects an OC71 without the black paint.

But there was more to it than this Transistor manufacturing of the time gave significant variability of transistor parameters, especially between batches.

Accordingly the different types were often as a result of a selection process. The OCP71 was selected for better light detection, and it was also packaged differently.

The basic OC71 transistor device itself was dipped in a light blue putty material and then covered in a paste that reduced light transmission and conducted heat away. Finally the device was encapsulated within its glass package which was painted black and marked. The reason for this light protection was to ensure the performance remained constant whatever the light levels.

The OCP71 was packaged differently using a clear silicon grease that gave much better light conduction as well as providing heat transfer away from the semiconductor device itself.

As the OCP71 was sold at a higher price than the OC71, many people removed the black paint.

There were stories that the manufacturers started to introduced OC71s with a black silicone grease within the glass encapsulation.

This reason was actually because the black paint on the OC71 would often peel or be rubbed off, making the OC71 transistors sensitive to light - an effect that caused problems in service.

To overcome this the OC71 silicone grease was change to a black version so that even if the paint peeled, the transistor would operate as normal.