Rick Campbell's One Transistor Amp Article

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AB2EZ:
Here are the LTSPICE simulations for the 1st stage:

L= 100uH
V1 = 12.8V
V2= 0.1V peak-to-peak, 7MHz

Blue= base-to-ground: 0.95V average (DC) value and 0.1V peak-to-peak
Green = emitter-to-ground: 0.085V average value (DC) and 0.08V peak-to-peak
Red = across the 50 ohm load resistor: 0V average (DC) and 1.25V peak-to-peak (some distortion)

Voltage gain = 1.25 V / .1V =12.5
Average collector current = 28.4mA

Stu

AB2EZ:
Here are the LTSPICE simulations for the 2nd stage:

L= 100uH
V1 = 12.8V
V2= 1.25V peak-to-peak, 7MHz
Note R4= 900 Ohms

Blue= base-to-ground: 1.6V average (DC) value and 1.25V peak-to-peak
Green = emitter-to-ground: 0.64V average value (DC) and 1.17V peak-to-peak
Red = across the 50 ohm load resistor: 0V average (DC) and 19.4V peak-to-peak (some distortion)

Voltage gain = 19.4 V / 1.25V = 15.5
Average collector current: 214 mA

Stu

AB2EZ:
Here are the LTSPICE simulations for both stages:

L= 10uH [As long as L>10uH, the value of L doesn't matter]
V1 = 12.8V
V2= 0.08V peak-to-peak, 7MHz [Note that I have reduced the rf input slightly from 100mV to 80mV peak-to-peak]

Note R8= 900 Ohms; and I have also removed the 1st stage's 50 ohm load. That is: the combination of R2 and R8, and the input impedance of the 2nd stage's transistor, is now the rf load on the 1st stage. I have also added a 50 ohm equivalent series resistor, R5, to the input rf source (V2).

Blue= stage 1 base-to-ground: 0.95V average (DC) value and .057V peak-to-peak
Green = stage 1 emitter-to-ground: .085V average value (DC) and .045V peak-to-peak
Purple = stage 2 base-to-ground: 1.6V average (DC) and 1.21V peak-to-peak
Red = across the 50 ohm stage 2 load resistor: 0V average (DC) and 18.8V peak-to-peak

Voltage gain = 18.8V / .08V = 235
Average stage 2 collector current: 216 mA

Stu

WA1GFZ:
good luck running a 2N3866 at that current

AB2EZ:
Frank

I believe you!

I think the 2N3866 is the wrong choice for operation at this frequency and this power level:

a) It has too low a value of HFE (beta), in general; and certainly at collector currents above 50mA
b) Its fT (unity gain frequency) is much higher than is needed for this application... leading to stability problems with simple layouts that would normally be adequate for this application.
c) Its maximum power dissipation rating is marginal for this application.

Once SWL gets the hang of things... he will probably need to switch to a different transistor in the final design.

Stu

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