From a 1967 document we extracted this simple audio amplifier circuit which should provide something around 2W of power with excellent sound quality depending on the output transformer and the speaker.
The tube is a double triode-pentode and the critical components beyond it, are the transformers. The values of the components are given in the list below:
R1 - 10 to 20 ohm x 5 W - wire
R2 - 1k x 5W - wire
R3 - 330 ohm x 1 W
R4, R7-470k x ½ W
R5 - 4k7 x 2 W
R6 - 82 k x ½ W
R8 - 300 ohm x 3 W
C1a, b = 50 + 50 uF x 150 V
C2 - 1 uF x 450 V - polyester
C3, C4 - 22 uF x 12 V - electrolytic
C5, - 10 nF x 250 V
C6-22 nF x 250 V
C7 -4.7 nF x 200 V
T1 - 125 V x 30 mA and 6.3 V x 2 A - Transformer
T2 - Output transformer with 3 to 5 k of primary and secondary according to the loudspeaker.
In figure 1 the complete diagram of the amplifier
