Tuesday, July 31, 2018

K2539 Amp rebuild

This is my new go to amp. ( I may remove the first stage.) It is almost to high gain. The one I made last night was great BUT I added a switch and rearranged the circuit in the build I did tonight.
 The lower one was a 1-1/2 volt Germanium transistor version of the hearing aid amp. The smaller board on top is the 9 volt JFET version. It worked so well I decided to do another and add a switch and battery tie points. To test it I connected 2 DVM's set on the 200 mv range and a signal generator. I have the ear buds plugged in so the reading are loaded values.
 Let's see .03mv = 30 uv input and 11 mv out, very good.

 The amp was to sensitive. It would hum when i put my hand close to the input. I placed a 1nfd cap and 510 Ohm resistor across the input. This helped bypass noise to ground. The readings were all taken with the input bypassed.

The next step will be to place an attenuator on the input and a demodulator to feed it. I thinking Gilbert Cell.
I'm still considering removing the first stage. I clipped a diode with a antenna across the second stage input and hear my local station. It may need the first stage for weak signal reception????? Time will tell.

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