Study of Kaneta method's bipolar symmetrical amplifier
Kaneta method's DC amp series
No.139 was astonishingly simplified, so
many people thought this amp is for the beginners.
But this amp has some problems about stability of final stage.
I had no skill to copy this amp, so I approached this amp from a different way.
Problem no.1 How I select 2N3055
At that time I didn't know how to measure hFE of transistor, I measured gm
couppled FET and bipolar transistor totally.
1 kHz sinewave by 0.205V was
putted in, and read voltage of output level.
12 pieces were measured.
Problem no.2 Thermal compensation
Coupled with FET which has
negative thermal coefficiency. This is named
turtle on turtle.
After assembled A606 is going to be
heat up, so I added cascade transistors
in order to supress collector loss.
Original circuit is a design of which current regulator of the first stage supresses
2nd and 3rd stages not to heat up.
Problem no.3 Harsh tone
By hearing test there was a Harsh tone. I thought setting point of current was
wrong. Consequently this tone dissapeared by removing emmiter R . It is clear tone
though it is rather unstable.