Here's an ultra simple mount you can make with scrap components. It is a simple experimental intercom. With the switch S2 in one position you speak one speaker and the other one plays. With S2 in the other position, you reverse the functions. Project for STEMers.
The circuit is powered by 4 common batteries and the transistor can be of any general PNP type of use such as 2SB175, BC307, OC74, BC558, etc.
Transformers can be taken advantage of old transistor radios out of use but must be of the output type, ie they are connected to the speakers in the original circuits. In figure 1 we have the complete circuit of this simple intercom.
In figure 2 we have the assembly of the apparatus based on a terminal strip.
The connecting wire to the remote speaker can be up to 10 meters long. The volume obtained will depend on the gain of the transistor used and the characteristics of the transformers.
The resistors are 1/8 W and the capacitor is not critical and may have 4.7 to 22 uF capacitance. The S2 switch is for the talk / listen function. You must change the position of the key when you switch from speaking to listening on a speaker.
The speakers can be of any type, giving preference to the small ones, of 5 cm, since they must be handled more easily sometimes being placed in the ear, or as microphones.
Material list
Q1- Any general purpose PNP transistor
FTE1, FTE2 - small speaker
T1, T2 - Output transformers - see text
B1- 6 V - 4 small batteries
S1- Single switch
S2- 2-pole x 2 positions
C1 - 10 uF - electrolytic capacitor
R1- 47 k ohm x 1/8 W - resistor - yellow, violet, orange
R2 - 10 k ohm x 1/8 W- resistor - brown, violet, orange
Miscellaneous: terminal bridge, battery holder, wires, solder, mounting box, etc.
