Hello, I can't seem to find the first all BJT audio amplifier. When and who invented it?

 

https://en.wikipedia.org/wiki/History_of_the_transistor

 

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

 

Thanks guys, you just saved me hours of pointless search!

 

Here is a Philips transistor radio circuit designed in 1955:

 

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.

 

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.

 

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

 

Another classic push pull looks alot like above. ( p12 figure 7 )
Trying to convert vacuum tube amplifiers to transistor was really frustrating. Using a curve tracer was helpful.
https://worldradiohistory.com/BOOKS...plifier-Manual-Bernard-176-Clive-Sinclair.pdf

The CK 721 CK722 pair were popular
1956 Popular Electronics 4 Transistor Receiver | OneTubeRadio.com

 

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.

 

The first all-semiconductor (i.e. no transformer coupling) power amplifier was H.C. Lin
https://worldwide.espacenet.com/patent/search/family/024011745/publication/US2896029A?q=US2896029
patented May 1955
https://www.aireradio.org/articolipop/articoli/img/HCLin_Quasi-Compl-Amp.pdf
at 1% THD, its distortion was an order of magnitude worse than valve amplifiers such as Williamson and Leak which managed 0.1% a decade earlier.