The Knight Space Spanner

I had one of these as a kid, this is not the same one, but one I reacquired.  If you have never used a regenerative receiver then you missed out on a lot of fun.  This is a three tube radio, basically a one tube regenerative detector with rectifier and audio stage.  You had to keep one hand on the bandspread and the other hand on the regeneration control, as the tuning was very touchy.

The theory of operation is that the received signal from the grid circuit is amplified to the plate circuit, then fed back into the grid circuit, using a "tickler coil", regulated by the regeneration control.  The signal is re-amplified over and over until the point of oscillation is reached, when the speaker howls and squeals.  You avoid this by adjusting the regeneration control just below the point of oscillation.  At this point the receiver gives maximum sensitivity and narrow selectivity, so you can pull in stations from around the world.  Quite amazing performance for such a simple circuit.

These radios were offered in kit form, and in 1965, Allied radio of Chicago sold them for $19.95.  Going back even further was the Ocean Hopper kit, I think it originally sold for $12.95, less case.  It was similar, but used plug in coils for band changes, and did not have a speaker.  The Space Spanner accepted headphones also, as you can see from the back view, a switch cut out the speaker and switched over to the pin plug jacks that were common for the time period.  I had a pair of 3000 ohm headphones, cheap generic variety, that I used with the crystal sets I built in the 4th grade.  I had them until they fell apart.  The cords were a flexible cloth that actually did not have a wire inside, but were woven with thin metallic foil stands in the cloth, making it impossible to solder to.  Crimping was the only method.  Some old cloth telephone cords were made in the same fashion.

You will find some websites describe this set as a "Superregenerative".  That is not true.  A superregenerative is a simple self oscillating vhf detector, that would receive AM and FM, like used in the Heath Twoer, Sixer, and Tener.  The superregenerative detector achieves high sensitivity, by amplifying to the point of oscillation.  Once this point is met, the device, (tube or transistor), is biased by its component values, to drop out of oscillation, and the cycle repeats.  The oscillation is said to be "quenched".  The quench frequency is at the ultrasonic rate, 20 to 30 KC (Kilocycles or kilohertz if you please).  These detectors yield a loud hiss with no signal present, and sets that used them were nicknamed "rush boxes".  Another place you found this detector was in the cheap Toy type walkie talkies, employing only 3 or 4 transistors, such as the Knight-Kit C-100, shown later in this section.

NEXT:  Interior views and schematic