EMI research laboratories multi-way mixer TG12345 transistors

At your risk.
Any voltage or current can be dangerous.
All safety precautions should be followed.
A fuse must be connected in series with any battery.


This is not a schematic or a circuit diagram of the EMI TG12345. Just a circuit description.


Most of the transistors used are BC109.


It must be an excellent choice by the genius electronic engineers who designed such great quality equipment.
Here is the datasheet of BC109.
https://www.fecegypt.com/uploads/dataSheet/1471183143_bc109.pdf


For example the input amplifier 'D' uses 3 BC109.


0.47μF capacitor sends input signal to base of front end BC109. Approximately 390KΩ must be from base to ground.
Collector load resistor is 75KΩ.
These resistors should be of excellent low noise quality.
8200pF is connected from collector to ground.
Collector is also connected directly to base of following stage BC109.
Emmiter is connected to a rather complex circuit network of resistors or capacitors. The other 2 terminals of said 3 terminal network is connected to -20V and gain control.
The first stage is supplied by +V at the collector resistor, see following text.


2nd stage BC109 has a collector resistor of 43KΩ apparently of special low noise quality. Emitter is connected directly to ground.
Just like Pleiades one transistor or one electron tube battery amplifiers operating as well in class A (electrons flowing all the time).
32μF decoupling capacitor is connected, minus to ground, + to the other side of collector resistor.


62K special quality series resistor to Vb=20V
So in fact the first stage is supplied by less than 20V at its collector load resistor.


Collector of 2nd stage is connected to base of third stage BC109.
It is an emmiter follower.
So emmiter resistor is 2.4K in parallel with 150pF.
Collector directly connected to Vb=20V
Output terminal is the emmiter of this transistor.



Ground is 0V.


The gain control circuit is as follows:
220mF positive side connected to ground.
Negative side of this capacitor connected to 360Ω and some other resistor.
The other sides of said resistors are joined and connected to 1st stage BC109 collector. And also to negative side of another 320μF.
Positive side of said capacitor is connected to 100Ω.
Other side of said 100Ω resistor to gain control terminal.
Other side of unknown resistor is connected to 11KΩ.
Other side of 11KΩ resistor to -20V.


Unknown resistor might be a variable resistor from 1KΩ to 5KΩ?


See forward in time post for the output stage of TG12345.