the first BJT amplifier audio

Delta Prime

Joined Nov 15, 2019
1,311
But if you want to go pro audio. :)
The first Solid State Circuits Conference, established by the AIEE-IRE, was hosted by the University of Pennsylvania in Philadelphia, PA in 1955. The meeting was held in the Irvine Auditorium of this University. Here, a late-news presentation was made on "Transistor High Fidelity Audio Systems", by Richard F. Shea of the General Electric Company (GE), Syracuse NY.
https://ethw.org/First-Hand:The_World's_First_Transistor_Hi-Fi_System
 

MrChips

Joined Oct 2, 2009
30,983
Philips OC71 amplifier.jpg

OC71 is a PNP germanium transistor. The +12V supply shown in the circuit schematic above is incorrect. It should be -12V.
OC71 is a small signal transistor with max. collector current of 50mA. It was later replaced with OC72 (max 250mA) for the output push-pull stage.
 

Audioguru again

Joined Oct 21, 2019
6,761
OC71 is a PNP germanium transistor. The +12V supply shown in the circuit schematic above is incorrect. It should be -12V.
OC71 is a small signal transistor with max. collector current of 50mA. It was later replaced with OC72 (max 250mA) for the output push-pull stage.
Good catch.:)
 

MrChips

Joined Oct 2, 2009
30,983
I grew up building transistor circuits with OC44, OC45, OC71, OC72 from Philips and hence their circuit applications are engraved in my brain.
 

MrChips

Joined Oct 2, 2009
30,983
Sir Clive Sinclair's transistor design publications are classics. I have a few of them myself.
I still have the Sinclair Project 60 and Z-30 power amps.

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