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Fig. 1 shows a simple circuit that I use around the workshop when I need isolated 117 volt a.c. The circuit also provides a handy source of low voltage a.c. for test set-ups. Be careful not to exceed the power rating of the transformers.
Fig. 1. Back to back filament transformers provide a source of isolated 117 v.a.c.
T1,T2 6.3 V filament transformers.
The circuit in Fig. 2 has two audio output transformers back to back and allows an ordinary audio amplifier to be used as a modulator. The Class C load should have a value close to the high impedance value of the transformer T4.
Fig. 2. Makeshift modulator using two output transformers.
T1,T2 Audio output transformers.
Donald R. Wesson, K4HCZ.