The 100 ohm volume control
The 100 ohm potentiometer shown in the figure is noted as 150 ohms in MJ issues, because MJ and Sakuma do not want to be annoyed with too many suggestions and questions from MJ subscribers.
If you accept the theory, a 150 ohm volume pot must be installed between the transformers which have a 150 ohm secondary and 150 ohm primary.
The miss-matched resistance works as a tone control, not as a volume control.
Sakuma accepts 100 ohms after a lot of testing.
The position of volume control
Theory tells us that the volume control must be installed between the driving transformer and the grid of the tube driven by it(See figure 3).
But Sakuma installs the volume control between the input and driver
transformers to get better sound.
I will correct the mistakes shown in MJ magazine as far as I can, however if you have a question, don't hesitate to send your mail to me, Takuji Yamamoto(takuji@cc.osaka-kyoiku.ac.jp).