Noisy Regen Circuit Review.

In the world of regenerative receivers it does seem to be the only circuit that is repeatable and reliable. At the very least you get a good Q multiplier. The tricky question is how to link a proper AM detector to the circuit. What ususally happens is AM detector input impedance shifts with signal evelope disturbe the delicate balance of forces that make the circuit a good Q multiplier.

Taking a signal from the emitters is generally safe as that is at low impedance. However low impedance means low signal voltage.

Taking a signal from the tuned circuit to feed into an AM detector requires great care about how the AM detector is designed.

What is also interesting about the noisy regen is it is a negative resistance circuit. An increase in the voltage at where the tuned circuit is connected to the collector of transistor A and base of transistor B causes an increase in current flow through transistor B and cuts off the current flow through transistor A. Therefore the current flow at collector A falls with increasing voltage which is the opposite of positive resistance.

Also if you couple the noisy regen circuit to a tuned circuit instead of connecting it directly to the tuned circuit it doesn't matter which way round it is coupled, which is different to how a normal tickler coil cares about turn direction.

@Sean O'Connor:

The tricky question is how to link a proper AM detector to the circuit. What ususally happens is AM detector input impedance shifts with signal evelope disturbe the delicate balance of forces that make the circuit a good Q multiplier.Taking a signal from the emitters is generally safe as that is at low impedance. However low impedance means low signal voltage. Taking a signal from the tuned circuit to feed into an AM detector requires great care about how the AM detector is designed.Taking a signal from the emitters is generally safe as that is at low impedance. However low impedance means low signal voltage.

You can also connect an RF interim amplifier between the emitters of the MC1648-based differential pair regenerative stage and a voltage doubling diode detector. See circuit diagram below. Best pratice is using a cascode or a Long Tailed Pair RF amplifier to isolate the diode detector from the tank circuit in any regenerative receiver.

I am in component count minimization mode, for a number of reasons, including just time limitation factors (the amount of time I have available to build things). I fully agree you could buffer the output of the Q multiplier and then use say a diode detector whose input impedance varies all over the place with signal envelope.