Murphyv310 wrote:Results with the resonators "seem" OK with a nice sharp IF response. For a single conversion the set works well although it is quite noisy on weak signals, quite typical of transistor sets of its age.
OK, seeing as it's only on the emitter resistor rather than main signal path/base, even a capacitor might work well enough. Perhaps the original even was a resonator and not a filter. Also some cheap oscillators may use cheap IF filters.
I'm about to do a write up on Tesco's current less than €7 (£5 or £6 in UK?) AM/FM portable radio. A cheap source of radio parts to make a crystal set, Valve IF transformer or battery valve radio or FM or AM modulator.
I've proved a pair of sub miniature MW coils (with ferrite rod) in an alloy medicine can with 220pF capacitors make a nice double tuned valve IFT at 440 to 480 KHz (adjust rod) and about 1cm spacing between the coils (on separate rods) gives narrowest bandwidth.
Quad gang polycon with 4 preset HF end padders. The VHF parts are fine to tune SW.
10.7MHz and 455KHz ceramic filters (no use for valve circuits)
8 pin IC (1.8V to 5V) headphone / speaker amp, class B. Use the amp, case and speaker as a little audio monitor, add a diode probe...