Yup, I'm not just build audio amplifiers, short wave regenerative radio is fun to build too.
I build this regen radio for daily listening, I can get 20++ stations loud and clear using high Z head phone in evening. This small radio can drive a speaker with stronger/nearby stations such as local station, Singapore, Indonesia, Thailand etc. I choose 6N1 or 6DJ8 because it can operate at higher current and lower Rp, easier to drive a small speaker. 6DJ8 is louder but a bit less sensitive than 6N1.
The coil is 3 inch diameter paper bobbin and consist of 14 turns of tuning coil tapped at 6 turn, 2 ½ turns for regen coil and 3 turns for antenna coil. All windings using SWG21 gauge wire.
Big coils and air gap type variable capacitor give higher Q factor and increase selectivity. The regen control VR is only 1K, it give less regenerative feedback for easier control. The two small trans are actually 1W output transformers, one for choke load and another for output purpose so that I can use 8 ohm speaker or head phone.
The antenna that I used is actually a 30 feet wire that tied on top of my roof. It can perform much better if I use proper build antenna. I even tried a 20 feet wire on a bamboo that fix on top of my front gate pillar and it works fine too. I didn¨t measure the frequency range but from stations that I had received,I think it¨s from 6MHz to 14 MHz.
It is always a problem for beginners to tune a regen radio into correct operating condition. Turn the regenerative VR to minimum and slowly increase, until hiss and whistle sound occur, then turn back a bit, select a station and then carefully turn the regen control again for best result.
My friend who even don't know which end of soldering gun to grab, build one of this radio successfully, the only mistake I notice is the polarity of regen coil is inverted, it will not operate until I change the polarity of the coil. Not polarity actually, just the phase of the coil, inductors have no polarity. ;)
Schematics can be download here.