Regenerative Receiver Hints
You don’t know what frustration is until you have tried to use a marginally functioning regenerative receiver as a communications receiver. Then I guess marginally functioning equipment of any type would frustrate the user. It is just that regenerative receivers have so much more to become frustrating.
Drift, hand capacity effects, flakey regeneration control, dial setting jumps when you touch it, headphones are uncomfortable, not sensitive enough normally and when you increase sensitivity, you can’t keep the signal tuned in. Those are just a few of the ‘fun’ experiences you are opening yourself up to.
Here are a few tips on how to deal with these frustrations.
Choose your tuning capacitors and dials very carefully. Ball bearing capacitors and zero backlash dials are best. If it is good enough to be used in building a VFO, it will probably work fine in a regen.
Wooden cabinets are fine but the front panel needs to be made of metal and connected to ground to prevent hand capacitance effects to the circuitry. Any part of the circuit could be effected by hand capacitance, not just the coil.
You don’t need RF amplification but you could benefit from RF isolation from the antenna. A grounded grid triode amp at the input will prevent the antenna from loading down the oscillator.
A triode makes a decent regenerative detector but a pentode makes an even better detector and allows smooth control of the regeneration threshold by varying the screen grid voltage.
The screen grid voltage to the detector needs to be well regulated. Using a VR tube here is a good idea.
Although a pentode detector has good output, it is not good enough to drive a headset under all conditions. Follow the detector with at least one audio stage before the headphones.
If you want speaker volume, then add another audio stage (maybe a 6V6) after the first.
If you have kept up with the tube count we are now up to five tubes. We might want to re-evaluate the design. Maybe go with a single conversion heterodyne.
Run the radio off batteries or a separate AC power supply. With the high sensitivity of the detector it will be nearly impossible to keep hum out of the radio if the power supply is built into the radio case.
You probably decided on a regenerative receiver thinking it would be a simple project. It can be simple but to get decent performance the regen becomes as big a project as a simple heterodyne.
Also, the same problems you experience using a single conversion heterodyne at higher frequencies also plague the regenerative receiver. At the very least, stability will suffer. Even so, both of these receivers can do very well on 80 and 40 meters. There is absolutely nothing wrong with using a crystal controlled converter, making the system a dual conversion, regardless of whether you decide on a single conversion heterodyne or regenerative.