- I thought it would be interesting to see how regenrx members would build the Neophyte receiver today, 50 years after its publication. After all, things are different now. Different parts are available, or not available. We understand (I think) regens better than most people did back in 1968. Certainly we appreciate them more.
Anyway, I uploaded my version, filename: neo-neophyte 1. Take a look and tell me what you think.
I used a 12JN8, triode+pentode, instead of the original 6U8A. I chose a 12V heater tube because the PS uses double 12V transformers (a common post-2000 ploy) for the B+. The 12JN8 is available in 6V/450mA and 19V/150mA versions too. Specs seem to be good for this kind of radio. It has an IS. And it can be found new for as little as one dollar from online tube sellers. Another example of those neglected TV tubes people aren't interested in these days.
Most of the component values are not at all critical. Of course, I haven't built this, so nothing is proven or optimized. But it should work fine with these first stabs.
I used a shunted tickler coil, with feedback from the screen grid rather than the plate, rather than the original Hartley. This comes from the Knight Kit Span Master. I think it's easier to make and adjust a tickler coil than to find and make a suitable tap for a Hartley. Anyway, I know this design works well, with very little frequency shift as the regeneration is adjusted.
There are two antenna inputs: a lo-Z input coil with RF attenuator for tuned antennas, and a hi-Z for short lengths of wire to be connected to the tank. The switchable small caps act as simple matching devices. The values reflect my experience and antennas.
The value of the regeneration pot and its bracketing resistors needs to be established in a prototype. Still, the indicated 100k pot plus 33k resistor should work OK as a start.
The switchable 0.047 cap across the audio output transformer is to cut hiss for CW. Of course, that value needs to be adjusted for personal preference.
The triple section PS filter is overkill I suppose, but electrolytics are cheap today, so why not? Also, large filter caps can act as simple voltage regulators. I expect current to be around 7 or 8mA (most of that for the audio stage), so voltage drop across the two 500 ohm resistors is negligible.
The heater is floated and sealed, to minimum hum. The heater wires of course should be tightly twisted and kept close to the chassis.
The tank coil is to be 2uH, giving a tuning range of about 5.6MHz to 16MHz or so with a standard 365pF main tuning VC and 15pF bandspread. The bandspread will still need a reduction drive (or another very small VC to act as a fine tuning control).
Anyway, this is how I would build it. Tentatively. I hope you'll all find ways to improve it. How about some other variations on this theme of the one tube triode+pentode regenerative receiver? Perhaps a 12V B+ version? I believe there is one low voltage triode + pentode tube out there.
- I neglected to say that my version assumes the builder will be using 16 or 32 ohm stereo phones, not the original design for 2k cans. That's why it's got an audio output transformer. I think there will be enough audio gain for stereo phones, but I'm not sure.