Note the chicken head knob.
I've read this sold for about $20USD in 1970 which in today's money (2017) equals $128USD
Just 4 resistors, 2 caps , a transistor and a pot.
R2 = 1M
R3 = 100K
R4 = 10K
R5 = 390R
R6 = A100K (volume pot)
C1 = 100nF/0.1uF
C2 = 100nF/0.1uF
It's interesting that C2 is ceramic & C1 a polyester.
I think they are just coupling caps to pass the wanted audio (AC) signals, while blocking any DC.
The first part of the circuit (C1 & R3) works a bit like a high pass filter.
Increasing the value of C1 should let in more bass. If you decrease it, more treble should appear.
With 0.1uF, most of the input signal goes through.
R2 & R2 forms a voltage divider. It determines the bias at the base of the transistor
The ratio between R4 (collector resistor) and R3 (emitter resistor) controls the gain of the transistor.