Why a defective amplifier ?
As a result of extraordinary practices on the amplifier and the relevant sound systems.
Where was the defect ?
The right channel of the stereo amplifier was partially destructed, and the sound level from the right channel was very low.
What was the leading idea ?
Not to discard the amplifier.
Then,
The idea "a stereo amplifier with an intact left channel can be used as a mono amplifier, connected to just one speaker, while giving the sounds of both channels" blinked.
Readings and practice
It was learned that "just putting left and right channel inputs into one common channel before entering the amplifier is not appropriate and may cause damage to components of the system".
One of the common practices to achieve the goal was found to be "placing 1 kiloohm resistors to each channel input lines just before making them one common line".
The common line was then made the left input channel for the amplifier, and only the left speaker output terminal was used to supply a speaker.
Audio test songs were run. Left channel sounds were OK, right channel sounds were OK.
