Monday, March 13, 2017

Lambda diode oscillator using discrete JFETs

lambda diode

edit 3: The circuit consist of the lambda diode, a coil, and a 3 volt supply. It is driving a diode ring mixer.

edit 2: The current peaks and then drops off when the supply voltage is increased. The 200 ohm resistor is not needed. the waveform appears smoother without the limiter resistor.

edit 1: I was playing with the lambda using J112 and J176 JFETs. With them connected face to face. The JFETs Mr Vargas uses have a different pin out. It worked for me so I had to look closer. The JFETs I'm using are symmetrical so the drain and source are interchangeable. My odd ball circuit was working the same because the device would allow me to connect it backwards and still work. 
After discovering this I did another with the pins matched as shown and it did seem just a tad better.

I was looking at the Lambda diode and found this article which is about building IET ( Instantaneous Electronic Trips) Using a J112 and a J176 to build the portion of the circuit labeled T1 and T2 produces a diode that will peak at around 5 - 6 ma and drop to zero at 12 - 15 volts. The perfect Lambda for a quick and easy oscillator. I put a 200 Ohm resistor from T1 drain to +Vcc and a tank from the source of T2 to -Vcc. She sings! I put the prototype in a project box with a RCA jack for the coil. It oscillates with the coils from my GDO from a few 100 Khz to beyond 10 Mhz.

Clipping that with my Double Balanced Mixer and hearing aid amp makes a good performing radio. It was oscillating with a 3 Volts supply. I'll have to put the pieces together in one chassis.

I think a regulated power supply and slug tuning will produce a winner.

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