Magnetic tape recording and playback system designed for low voltage dc power sources

Claim 1

In a DC powered magnetic tape recording and playback system having a magnetic tape transport and at least one channel having a speaker, recording and playback head, and an erase head arranged to cooperate with said transport, a combined bias supply and internal DC voltage doubling supply circuit comprising: a transformer with a core, a primary and a secondary; a pair of solid state switching devices operably coupled between a DC source and said primary to generate a frequency of at least 30 kHz. in said secondary; switch means coupled to said secondary and said recording and playback head and said erase head to alternately connect said heads with said secondary; a pair of diodes and a capacitor with a common lead of each diode connected in a junction with one side of said capacitor, one of said diodes having its opposite lead commonly connected to one of said solid state switching devices and its connection to said primary, said other diode having its opposite lead commonly connected to the other of said solid state switching devices and its connection to said primary, said capacitor havIng its opposite side connected to a common ground with said DC power source; an amplifying circuit in said at least one channel having its signal input coupled to said recording and playback head, its output coupled to said speaker and at least one of its power inputs coupled to said junction of said capacitor and said diodes whereby a DC voltage higher than said DC source will power said amplifier.