I didn't make any mistake. Look at the original diagram. It has the numbering of the transformer pins. But I can change the pins of the secondary winding. I will do that a little later. I have to get home.Sir Kit only asked two questions:
Can anyone please tell me why the JFET's are wired in parallel?
(Answer: This increases the drain amps per gate volts, Gm)
What might be the purpose of the air core transformer?
Still a mystery.
Please stick to the questions
Hi,I received the plot below from another source who proposed that the negative feedback via the transformer could be intended to make the circuit oscillate.
Any comments?
See post #2Thank you for your reply. The propensity for this circuit to oscillate was not mentioned previously in this thread.
Well, okay and I did not mean that for the original circuit drawing but for the one in reply #27 where the phasing dot indicators are on the top of both coils. Member Bordodynov showed simulations for both cases of the phasing dot positions in his reply #25.Thank you for your reply. The propensity for this circuit to oscillate was not mentioned previously in this thread.
No it would not, IMHO. If the parallel LC tank would connect the common gates to the ground and no input signal to the tank is given (if you meant this, please correct if not), then such tank would isolate the gates from the ground at and near its resonant frequency with a relatively high impedance. So at this single frequency the amplifier would have a floating gate RF wise, making self oscillation hard to come by at least at that frequency. Of course at many other frequencies the tank may connect the gates to the ground (having low impedance) and the circuit may self oscillate at a certain frequency established by the air cored coupled coils. 12T on 3/4" dia. air core (from your reply #10) may represent around 2.8 uH inductance for each coil as per this calculator https://coil32.net/online-calculators/one-layer-coil-calculator.htmlWould the circuit self-oscillate if the "input" was a ground referenced, tunable tank circuit (in the MHz range) that produced little or no signal?
Well, it does not depend on that. The circuit can operate as an oscillator either with air or ferrite cored coils, this depends first of all on the coils phasings. You can read on this here in this paperIn your opinion, is it likely oscillation was intended by the designer given that the transformer is air core and not ferrite?
by Jake Hertz
by Jake Hertz
by Jake Hertz