I picked up this Knight Space Spanner several years ago in non-working condition. I have an entire shack full of non-working project radios. Actually, more than I have working radios. It’s a simple tube regenerative AM receiver with a selectable band for broadcast or shortwave. Think of Knight radio as the do it yourself branch of Allied Radio back in the day. They produced a wide array of radio kits for the consumer market. This model was produced from 1956-1964. It’s not great as far as receivers go. Even back in the day there were much better offerings available, but I’m guessing this was aimed more at the general radio listener than hams.
The regen is a funny beast with a history that goes way back to the early 1900’s. Tuning in a station is a balancing act between volume, regeneration, antenna coupling, and dial setting. Any mis-adjustment of any combination of these switches results in useless noise or screaming oscillations. The screaming oscillations are the worst! It might be wise to offer up a solid state electrical device as a sacrifice or recite ancient incantations prior to resurrecting one of these demons. But when proper tuned, a station does sound surprisingly nice. I’ve found it quite pleasant to listen to local oldies radio on the AM broadcast dial.
What it lacks in features it makes up in simplicity. Not a lot going on inside this small box. The schematic is simple to follow and the circuit is all point to point wiring. I’m sure it would’ve been an entry level project when new. Back then you had to be tough, though. There’s no transformer isolated HV power supply. All the tubes are lit in a series string straight across the wall line voltage. Insert the non-polarized plug in the socket backwards and you’ll get AC voltage on the chassis. I guess folks were just supposed to know better than to do that more than once! What I’ll refer to as a self-correcting error.
I’m preparing to rebuild a Hallicrafters SX-28 this year. That’s way above my current skill level and I need more practice. This Space Spanner seemed like the ideal candidate. It already didn’t work so I figured I couldn’t make it any more broken! I had to go at it in small spurts due to my busy work schedule. Overall, it’s been quite rewarding to make it play again.
It didn’t have any tubes so I started with ordering them from the web. Tried it out, but no love. I then removed the aged electrolytics. There were only three, and plenty of room to work. I also found a suspect ceracap. I don’t know anything about them, but replaced anyway. There’s a cap straight across the neutral to ground. I believe these are called a “death cap”. That was replaced with a proper XY AC-rated safety cap. Powered it up slow on a variac, hooked up an antenna, no smoke, and…no love! Not really even much noise.
Well, it took me a long time to get back to the radio again. This time I printed off the schematic and started tracing it line by line. I finally came across a mis-wired ceramic cap. I did nothing more than move it from one point on the terminal tie strip to the spot right next to it. This time it worked straight away! How awesome a feeling to bring it back from the dead! I wonder if it ever worked, or who mis-wired it. I also found an extra wire tack soldered that was removed during the repairs. I wonder what it was for. Repairing old radios is often a mystery.
I always seem to learn something new after each repair. Each case is unique and I rarely turn up a unicorn that work perfectly straight away, have never been touched by human hands since construction. I guess I’m about up to 1960’s skill level. With any luck I’ll progress to the 21st century by the time I retire! Maybe not, old radios have more soul than modern stuff. I’m glad to keep another piece of history from the landfill.
The first stage of fixing up this old transmitter is disassembly. When Johnson built their gear they certainly didn’t spare the fasteners. This thing is held together by a ton of slotted head screws. Took forever to remove them all. Fortunately, the cabinet came apart really easy. The hardest part was removing the front
I now have access to the chassis of the beast. I’m impressed with the overall design, construction, layout, and quality. You can really tell these were built to last. The top side will definitely need some scrubbing, but I don’t see rust or corrosion. Of specific interest is the ganged, gear-driven variable inductor/capacitor tuning unit. Not only is it exceedingly grungy, but it’s not operating correctly. I believe this is the only item of concern up top.
I’ll also have to do some checks on the resistors as they’ve probably drifted, too. Some components are more critical than others depending on the particular circuit. This will just take some time to research the usual suspects and start ordering.
Here’s a pic of this big honkin’ oil filled cap. No reason to include it except it’s cool. Just another example of the quality put into these rigs. Hoping to get the chassis all cleaned up and the roller inductor functional again. That will complete the first phase of the project. I think the next part will be more fun. I like working with components better than cleaning stuff up. Stay tuned.
With the circuit fully complete, this amounted to a one day project to get the basic assembly done. I found a suitable Christmas tin for a cabinet. The majority of my time was spent laying out and marking holes for the board standoffs and all the jacks and pots to be connected. It’s not exceedingly elegant but I 
was able to accomplish it all with a hand drill, pliars, and a couple wrenches. I chose the metal enclosure because I thought It might provide good shielding. Eventually I’ll probably add a small fan and punch some holes for ventilation. There should also be enough room to add an Arduino, DDS or PLL board, and cool LCD display. I think it would make a perfect radio for portable operation with a battery and 40m dipole at the park.
instructions, reference materials, and purchase info. The product is sourced and shipped out of India and constructed by a local women’s collective that helps provide skills and jobs. They typically arrive in less than a month. Not bad turn around time. Easy ordering with Paypal.
I got energized to try something new after participation in the 
iver was a Yaesu FRdx-400. Early 70’s production, and it did pretty well for me, too. I didn’t yet have a dowkey relay so all the switching was done manually. Let me tell you, that’s a lot of work just to complete an exchange! My time was limited, and I made only one contact but I think the hook was set. Time to finally breath new life into this old gear that’s been sitting around cluttering up my shack.
n years ago I purchased a Johnson Viking II transmitter from a good friend and elmer Joel, K2LYC (now SK). I also came home with several other vintage pieces from his extensive collection, but that will become the subject matter of many future posts. The intent was to setup an AM station (Studio B) to accompany my then-modern Icom IC-756 station (Studio A). Somehow a decade passed away and, sadly, so did Joel. I guess I feel like I owe it to him to get this stuff playing again. So, it begins with the transmitter. I’m going to start there because usually they’re simpler. I’ve also had pretty good success fixing others. Fortunately, there’s loads of info available at my fingertips. This is the intro so I’m not going too deep. My plan is to remove the chassis from the cabinet for overall cleaning and inspection. I’ll replace any faulty components and perform only the mods that are proven and considered best practice. No total restoration needed. I’m sure every scratch and scrape tells a story. It’ll never be a mint specimen, just an honest workhorse. Eventually it’ll pair with my Collins 75A-3 (which will probably be the next project). But you see I’m already ahead of myself. Next post will start getting into the real heart of the job. 73!
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