Sunday, June 3, 2018

3 transistor AF amp build

I have to many projects on the bench but they all need a good AF amp so I'm working on more than one at a time here ;).

This is the amp. It is stable and high gain. I put a 50KOhm pot between C1 and the base of Q2 with another 68nf cap on its wiper. I connected my AF signal generator on the input and had to turn the pot down when the generator was set at minimum. With my finger on the input I hear 60 Hz. With an antenna on the input I still only hear 60 Hz. I put a ferrite core coil and diode across the input and hear a radio station. Sliding the core in and out I can select 3 or 4 stations. I removed the diode and hear little. It needs the gain on high to hear the buzz with the coil in the circuit without the diode. This is good! If you over drive an amp it will distort and detect a signal. The test tell me it is not over driving or distorting.

Not much to look at but it works as intended. I sliced a piece of material from a 2" X 4" board. Used the copper foil glass worker used when soldering up stained glass.I put a pin in each pad to anchor them. Couldn't be simpler.

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