Dave's One Tube Wonder — #26 Tube Crystal Radio
Are you afraid that when the big one is dropped, the electromagnetic pulse will wipe out your diode? Well, this crystal set may be the answer. Tubes don't get clobbered by those nasty pulses. I proudly announce to the world the creation of my one tube diode receiver.
You are now thinking - "Only an idiot would build a diode tube radio". Well you are certainly correct, this idiot did build one.
If you have visited my other crystal set pages, you will notice that many of my sets use the one coil, two capacitor circuit. That is because it works so well. For more details, please visit my #12 page.
What is new with this set is the inclusion of a vacuum tube. This is still a diode receiver as the tube is not powered for amplification. It could, if you wanted it to as there is a pentode section to this tube. The 1S5 is a diode detector and audio amplifier tube. I am using only the diode section. I attempted using an old TV high voltage rectifier tube, such as a 1G3, but the reception was very weak. So I settled for the 1S5. You can use other tubes. I even tried using the control grid as the diode plate and that worked also.
I use one of my link switches in this design. This type of switch looks very nice, but you could use a toggle switch and get the same results. When the switch link is moved towards the tube, the filament will light and the tube will be doing the detecting. When the switch is moved to the other thumb nut, then the diode is doing the work. This is a combination on/off switch and detector switch.
The coil is wound with 54 turns of 40/44 litz wire with a tap at 40 turns. This set is designed for use with a crystal earphone, but a high impedance headphone would also work. Sound powered phones can be also used, but the resistor should be removed and a transformer, pot and capacitor must be added. I will be covering sound powered phones in a future radio.
How does it work? Very nice indeed. The signal is louder with the 1n34a diode than the tube. A single D cell can provide many hours of listening pleasure, but the diode operates in the "Schmarder mode" aka free.
Best wishes and good DX. Dave - N2DS