24-10-2016, 11:25 AM
The twin 4.5V batteries (as compared to a single 9V battery) saved the cost of an output coupling capacitor. It was used in a few radios too. You could probably use a single 9V battery if you added a large (100uF+) capacitor in series with the speaker.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
