03-05-2021, 07:46 PM
Quote:A year or so ago I did have some success with a vhf circuit, (again an FM band superregen that used a twin triode for detector + AF amp that used a transmission line for tuning that I called a trombone tuner*. It was a U shape piece of heavy tinned wire, (think 100 amp fuse wire that had a coil incorporated on one end that was loading for the top end of the FM band), it was tuned by pulley and cord system that pulled a sliding contact along between the parallel section of wire. I have the notes and dimensions for that with the actual device, unfortunately not here! (In a biscuit tin two counties away!) The only real problem with that was having the connections to the valve from the tuned circuit short enough... That performed best with the detector changed to a UHF triode.Brilliant
Very impressive. You live following the true spirit of a radio experimenter. Your set-up reminds me his rig of measuring air variable capacitor loss using copper pipe transmission line:http://g3rbj.co.uk/wp-content/uploads/20...ssue-3.pdf
Certainly it would be much cheaper than building VHF cavity or helical resonator. Copper pipe of large diameter is expensive.
Quote:ore by luck than judgment the bandwidth of that tuned circuit was just right, and reasonably noise free slope detection was possible, and although a simple self quenched design, its quench ran at about 30 kHz and the audio is acceptably entertainment quality: listening to music with it, is a pleasant enough experience.
The squeal of 6C4 superregenative receiver hurts my ear. It was a simple weekend project. The theory behind ithe superregenative receiver fried my brain.
Quote:Hi Folks, why not go to the PCC84 as used in TV, it was a good reliable valve and seems to have had less problems than the ECC85, which got a bit of a bad name.
You could also go further and look at the UHF tuner valves PC86/88/97/900. Slightly odd heater voltages and only single valves but most electrodes are double pinned on the base for low inductance.
Also plenty around and really cheap
Ed i might try. I also have a pair of new 12DT8 (like 12AT7 but with screen between triodes) which i can try in my oscillator test rig..
