Space Spanner Success Story

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.

Crusty old parts removed from under the chassis

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.

View under chassis before surgery
New caps don’t take up nearly as much space

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.

This little ceramic cap from tube socket pin 7 to terminal tie strip is the culprit. Should’ve been landed on the first tie point.

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.

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I’ve been doing a bit of AM operating of late.  This vintage mode if fun to operate and sounds great when the band conditions aren’t too noisy.  I’ve also been repairing and tinkering with some old transmitters as mentioned in other posts.  One of the highest pursuits of the AM op is to achieve great audio.  Many will go to great lengths to buy studio rack gear with pre-amps, compressors, limiters, and EQ.  Top off all this hamsexy rack gear with a big old boom mic!

The other part of the equation is to properly adjust the audio modulation.  It’s not as simple as watching the ALC meter like on SSB (although it does help).  A first step is to look at the RF waveform on an oscilloscope.  You want to verify that the wave isn’t flat topping.  A modulation monitor can be used to view the modulation percentage.  Combine these two together and you get the AMM-SD1 by Radio Engineering Associates.  This slick device connects into the feedline and runs in software on the computer.  It’s pretty much real-time display shows the RF waveform and the negative and positive modulation percentage peaks.

Seemed like this might be a worthwhile investment for the shack…like I even need an excuse to by cool shack gear!  So far it’s confirmed that my AM audio is clean with positive peaks over 120% and negative peaks right at 100%.  Right about where it needs to be.  I’ve also used it to detect that the Ranger II I’m working on is in need of further inspection.  The positive peaks only hit about 40% before the stopping point when negative peaks hit 100%.  I never would have found that without the monitor unless trying to make a contact and some OM tells me my signal is crap.

This monitor has already proven to be an asset to my radio operation.  I just wanted to share it with my followers and encourage people to give AM a try if you like a little more than UR 59 OM, QRZ.  There are frequent AM operating events throughout the year, so there’s no excuse not to lay down some carrier and chat it up.

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Space and satellite operation is one area of ham radio I’ve yet to spend much time on.  I think it’s neat but I spend so much more time tinkering with projects and operating HF that there’s little time left for other pursuits.

I have previously copied signals from ARISSat-1 before its orbit degraded and it self destructed on re-entry.  That was pretty cool but it was just pre-recorded messages and some telemetry.  I was never able to copy the SSTV pictures.  I did learn that the low earth orbiting satellites can be worked with pretty modest antennas and radios.

Thanks to my friend Ed, NN9D for alerting me to a neat space opportunity.  Cumberland Elementary  School in West Lafayette, IN had arranged a contact to the ISS through the ARISS progam.  I had just enough time to go out and listen to the 145.800 MHz downlink in my car.  The pass was supposed to be a little over nine minutes and I think I was able to copy a solid seven to eight minutes.  Not bad considering I was listening on a third-hand Yaesu 1500M and a 5/8 wave vertical on the trunk mount.  It was really neat to hear an astronaut talking to the kids from 260 miles up in space, in real  time!  I couldn’t hear the uplink but could get a pretty good idea of the questions from hearing the answers.

The next day at work I saw that it made the front page of the Lafayette Journal and Courier newspaper. It was a nice article and gave some of the background info and details about the people involved.  The astronaut, Kevin Ford, is an Indiana native.  I thoroughly enjoyed the experience, and I can only imagine the students were impressed.  Job well done to all the students, teachers, ham volunteers…and the host, live from ISS, 260 miles in space!

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I’ve been in an old radio mode here lately.  I was born too late to really enjoy the old stuff when it was in prime use.  I guess watching those videos on regen receivers a few weeks ago must’ve done it.  So far I’m enjoying working on the old crystal set.  Even if it’s nothing more than a conversation piece for the shack.  I’ll be curious to see if I can pick anything up on it when it’s all back together.  After that I think I’ll attempt to build some variety of regen receiver for the 80 or 40 band.  Nick and I are looking into some plans for that and it appears that it can be done pretty cheaply.  I guess there’s also various levels of complexity depending on how well you want it to perform.

This week when I got my Youtube subscription I saw that MIKROWAVE1 (the regen guy) had some new videos.  I’m glad that I decided to subscribe to his channel!  He put together a five-part series on the ARC-5 transmitter series.  I’ve heard of them, but didn’t know too much about them being licensed only in the last ten years.  I guess these were quite available on the surplus market back in the day and were prime picks for new hams.  This fellow seems to be somewhat of an authority on these critters and goes into some detail on how they operate, the differences in army and navy versions, and some tips to put back them on the air.  And, like before, he does just that for our viewing pleasure.  You have to wait all the way until Part five, though.

It’s ironic that I feel like retro man with all the money I’ve sunk into the Flex-5000 and the Hexbeam setup.  I really like these modern advances, and the digital modes are great fun.  It’s such a convenience to be able to just fire up the station and go to it.  But, when I’m not in a hurry, and I’m not in the pileup fighting to work the DX, twiddling the knobs and warming up the old tubes sure is fun.  It just feels like REAL RADIO!

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It’s a dreary Sunday morning today here in Indiana.  I finally got around to hooking up the hamfest special HG-10 to the DX-60A.  For once I think I may have hit upon radio success on my first attempt.  The $40 VFO seems to be working just fine.  I haven’t even attempted to clean it up or check the tubes yet.  I just decided to plug it in and hope for the best.  I’ll still need to order a copy of the manual since Heathkit manuals are no longer freely available on the web.  Darn copyright laws!  I suppose it could use some tweaking and adjustment…and also a good cleaning.  Here’s a shot of the transmitter and VFO on the workbench.


I haven’t hooked it up to a microphone yet to check it out on AM but I have a D-104 that should go nicely with it, though.  Now I’ll have to work on one of my receivers so I can pair them up as a boatanchor station.  I did monitor my power output into a dummy load using the graphical display from my WaveNode WN-2 meter.  I keyed it up with my trusty old J-38 and seem to be getting normal output.  Not exactly enough power to be East Coast Control like Joel, but maybe good enough for a few QSO’s.


Just for fun I decided to tune in the output on the Flex-5000.  I wanted to see how far off the  VFO analog display is from the actual freq.  Well, I figured out the reason those old radios have a Spot function for getting the XMTR and RCVR in synch.  It’s not exactly dead-on like the new stuff!  Fortunately with the 96 KHZ display on the PowerSDR I quickly found the signal and was able to tune it in.


I’m glad to be free from the crystal now and able to move freely across the bands.  I think this is probably a decent investment given the cost of crystals for any frequency one may want to try to operate.  It may be a long cold winter so I should have plenty of projects in the shack.

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