Jara's Dual 1J24b Radio
I'm sending you my new project. It is simple reflex receiver for MW band with two 1J24b.
1/ Coils are from old Czechoslovak radio from 1950y for Hi-Z antenna. (Use antenna coil cca 1.5mH and tuning coil cca 190uH and also feedback coil. But I didnt use feedback here.)
2/ Variable capacitor is from old transistor radio from Germany - cca 2x 380pF - I need switch for all MW band because coil is for 500pF capacitor..
3/ Switch is from old Czechoslovak police transmitter...
4/ Variable resistors with knobs and black panel is from old Czechoslovak TV set.
5/ White board is box for 220V AC socket .
6/ Transformer TR1 is in feritte pot, 540uH / 250uH.
7/ P1 is "RF gain" (but also change audio volume!) I need it, because strong signals have distortion without setting!
8/ P2 is "bias setting" for diodes. If you use Ge diodes, you won't need it! Zener diode is for 4volt (but you can use other).
9/ P3 is "volume". But it isn't necessary - you can use only P1 for it.
10/ I think that you can try positive feedback, but I don't have not tubes and I had problems with feedback setting. (I use also 45V, minimum was 30V for good work). And: maybe is 1J29b better?
11/ Problems with feedback: I cannot set it with P1, because I also set here the audio volume. But if you use very small positive feedback, sensitivity will be better. (Set no oscillating in all band!)
12/ You must use shielded cable to P3, I think that it will be good also for anode of first tube.
13/ I use 40-45V "for all". Also for heating. But because I need cca 1.2V for heating, here is J310 and two 1N4007. It is current regulator and voltage stabiliser. (I have cca 1.15V for heating now.)
14/ Miniature russian tubes have low ampification - I cannot use lower voltage for anodes, but the receiver works well with a long antenna (100ft) also without feedback. (And I have old and used tubes only!)
15/ If you use Ge diodes and any other engagement, I think that you can use also AGC. But I didnt tested it. (1N5711 is schottky diode, very sensitive, but without bias has big distortion - lower distortion is with BAT46 - here you need not P2 too)
16/ Other small tubes work better also with lower anode voltage, but here are "grids" only as "rods", no "grids"! (See tube inside)
17/ My other idea, but not tested: use both tubes as HF amplifier and first tube with positive feedback. And only second tube also as audio amplifier... I think that here is not problem with P1 feedback setting...
Jara "Rat" Czechia
A very nice project, Jara. I can imagine that you took some time to make adjustments to get this working well. Thank you for offering it to my English language visitors.