Knight | Space Spanner

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Another Space Spanner!
 
Space Spanner
This Space Spanner was purchased on ebay in 2021 from a woman in Ontario, Canada.
It was built by a kid named Timothy Hodgson sometime between 1959 and 1963.
 
Space Spanner
The wooden cabinet looks new! I can't say the same about the front panel.
 
Space Spanner
Rear view.
 
American Bell Headphones
These American Bell headphones were sold with the kit by Allied Radio.
 
First look at the chassis.
The 12AT7 on the right is a GE made in Canada. The 35W4 in the center is the original Mullard, and the 50C5 on the left had no markings on it at all. The green shading on the back of the chassis shows it spent most of its life in the wooden cabinet.
 
Space Spanner
It's practically identical to the earlier model. It even has the big "CERACAP" capacitor on the left. The "CERACAP"
 tested perfectly good, which confirms my suspicion there was nothing wrong with the one I broke on the other radio (Page 2).
 
"Headache? Try CERACAP."

 
Here is the photo from the ebay listing. The radio came with the box, headphones and the original manual. It appears to be plugged in!
Notice the beautiful front panel. The photo is very misleading! The front panel looks different under different lighting.
 

 
 
This is how the light angle can change the front panel, and why the ebay photo was less than honest. I had to look at the ebay photo very intently to make sure it was even the same radio. The scratch over the word REGENERATION is barely visible in the ebay photo.
 
Sixty years of oxidation! This is how it appeared after it was cleaned and polished. It looked a lot worse when I first got it.
 
 
 
 
So who built this radio? Here's his picture and his fingerprint. His fingerprints are all over the radio chassis, burned into the oxidized cadmium plating. Using some information from the seller and her name from my PayPal account, I was able to find that the set builder was named Timothy Hodgson from Westport, Ontario, Canada. Tim's time on this earth was from October 17, 1953 to May 19, 2016. Since the radio was made between 1959 and 1963, Tim was TEN YEARS OLD or younger when he built it.

The ebay listing said he was a radio fanatic. In an email from the seller, Tim's widow, I learned that after he died she threw all his radios into a dumpster, except this one. She kept this one because it was light and had a box, but finally decided to get rid of it to "make room." She shipped the radio with no packing in the box. None whatsoever! How it made it from Ontario to Pennsylvania in one piece is a mystery. Perhaps it was guided by the invisible hand of Tim Hodgson.

Why would you throw working radios that may have monetary value into a dumpster? I've seen messages in radio forums that go something like this: "
User: Bob RadioGuy - This is Bob's wife. Bob passed away last week. I want to get rid of these radios ASAP, hopefully all at once. If nobody wants them, they are going in the trash. Please advise me on how to dispose of them."

Personally, I think some women begrudge their husbands having a hobby. If my wife had a hobby collecting sewing machines and she died, the last thing I would do is throw her sewing machines into a dumpster.
 

Repairs to the radio
 
This connection arrived broken. I had a hunch the radio would work better if it was reconnected. I was right!
 
 
 
Naturally, the electrolytic had to be re-stuffed. I spliced it in so I wouldn't have to mess with the tube socket connections.
 
 
 
After replacing the electrolytic capacitors the radio seemed to work OK, but wasn't very sensitive. I couldn't hear anything on the short wave band where the amateur radio guys are. Every part was checked, and this single resistor was out of spec. It's rated at 270 ohms but was actually at 350 ohms. Could that make a difference? I mean, it's only, like, 80 ohms. Granted, 80 ohms is about 30% off, but it's still only 80 ohms.

The resistor was replaced, and the radio came to life! Who would have thunk it? It picked up AWL KINDZA ham radios and shortwave broadcasts!

Except for cleaning up the front panel and chassis, that was about all the work that was needed. It had been assembled very well, and the soldering was mostly top-notch.
 
In the schematic, the resistor that was replaced is R-5, connecting the cathode on pin 8 of the 12AT7 to B-minus. (Click on the schematic for a larger version.) So here's a question; If the cathode on pin 3 doesn't need the resistor, why does the cathode on pin 8 need it? If lowering the value made the radio work better, what would happen if we just jumpered it with a piece of wire? Anyone? Anyone? Feel free to write to me at mike@mikesyard to explain it too me.

 
 
 
This stuff was found in the speaker when the front panel was removed. There's nothing unusual about dirt and detritus in an old radio, but how did this get through the little holes in the speaker grill and what is it? I'd bet this radio spent years lying on its back in a garage.
 

Testing the radio with the American Bell headphones, February 7, 2021.
 

 

Knight Space Spanner VS the Lafayette Explor-Air KT-135

 
Knight Space Spanner Lafayette Explor-Air

Is the Knight Space Spanner the "ancestor" of the Lafayette Explor-air KT-135? The lower part of the fronts are nearly identical. They both come in a wooden cabinet coated in a vinyl wallpaper-like material. They have the same controls and use the same three vacuum tubes.

Inspection of the two shows that except for the tubes and the AC cord, there is not a single interchangeable part in the two radios. The Space Spanner is 1/2 inch wider than the Explor-Air. The lower knobs are similar, but have a slight difference. The values of the volume and regeneration control are different, as is the value of the RF choke. The KT-135 has four bands, so the band switch is a different type. Every major part on the chassis is different and mounted differently.

The Space Spanner has a filter choke in its power supply. Lafayette used a much cheaper 270Ω resistor instead, but the cost savings was offset by the addition of two additional RF coils. Because the filter choke is missing on the KT-135, Lafayette added a third filter capacitor.

However, there are too many similarities in the two to be coincidental. Though the values of various components differ, the circuits are nearly identical. In addition, when the KT-135 debuted in 1958 with its two tone front panel, the Space Spanner suddenly sported a two tone front panel. It seems Allied radio was "watching" the competition.

 
 
 
 
  Space Spanner   KT-135  

One difference between the two are the headphone jacks and the way they are wired. The Space Spanner requires a high impedance headset, which were common in 1956. A switch toggles the audio between the speaker and the headphones. Today, high impedance headphones cost more than the radio, if you can find a pair. The KT-135 only needs a "regular" set of cheap mono headphones with a 1/4 inch plug.

The KT-135 appears to be a Space Spanner, improved with the addition of two more shortwave bands and a headphone jack. It has been speculated  that the Space Spanner was designed by Accurate Instrument Company while the KT-135 was designed by the Lafayette Radio engineering group. If this is true, those Lafayette guys must have been looking at a Space Spanner while they were working. Of course, it's now impossible to find any of the people directly involved to ask them.
 
The 1957 Space Spanner on the left is about ten years older than the KT-135 on the right.
 
 
Globe Patrol
Burstein-Applebee
 
  Archer Globe Patrol in homemade wooden cabinet. Very rare Burstein-Applebee from 1967.  
 
Two other similar radios appeared in the 1960s. The Archer Globe Patrol sold by Radio Shack and a rare clone sold by Burstein-Applebee. Look closely and you'll see that though the BA radio looks identical to the Globe Patrol, the front panel slopes back where the two colors meet. Like the KT-135, both had four bands. They all had "leatherette" covered wooden cabinets. It seems the Knight Space Spanner was the first of its kind and other companies followed.

For more information, see the article by Rich Post here.
 

 
THOUGHTS ON VARIOUS VACUUM TUBES USED IN REGENS
This is part of a discussion on the Antique Radio Forum concerning the Space Spanner.
 
(Beginning of post) ...Anyway, that aside, let's discuss triodes for regenerative detectors. It's often been claimed that low mu triodes make the best triode regenerative detectors. I agree but I add it's a combination of low mu and high transconductance that makes the best triode regens. Gm/mu is the defining relationship, which is of course the reciprocal of plate resistance. So a quick way to compare different triodes and their suitability to be regenerative detectors is to look at the plate resistance data: the lower the better.

(By 'better', I mean the tube easily and smoothly goes into oscillation (even with low plate voltage), control at the onset point is predictable, there is no hysteresis, no screeching, no jumping in or out of oscillation, etc).

Let's look at some popular tubes:

6AB4/12AT7: rp = 15K at 100V

6C4/12AU7: rp = 6.5K at 100V

6DR4/12AX7: rp = 80K at 100V

The 12AU7 seems to be the best choice. My experience is that there isn't so much difference between the 12AU7 and the 12AT7, but if I had to choose, I would take the 12AU7. I have made regens with the 12AX7: no problem getting it into oscillation, but control was not as good as the 12AT7 or 12AU7, a little finicky.

One tube that I've gotten particularly good results from is the 6/12BE6 pentagrid, triode connected. Mu is 20, gm a fairly high 7200umhos, and the rp only 2.7K. It's interesting to note that this tube in triode connection was used as the local oscillator in the Hallicrafters SX-28, and the company pointed out they chose it precisely for its high transconductance and low mu. The similar 6BY6, in triode mode, works even better (for me).

In theory, the best tube for the SS or GR-81 or Explor-Air would be the 12DW7: the 12AU7 section as the detector, the 12AX7 section as the audio amp. In practice, I don't think it would be worth the bother to make the necessary changes. Actually, I stopped using these double triode tubes years ago because they were too expensive. There are plenty of $1 tubes available that work at least as well.

Shinkuukan (Tokyo, Japan)
 

Note: "Shinkuukan" is just a handle. The word means "vacuum tube" in Japanese. Shinkuukan's real name is Rob. Originally from New Jersey, he's 72 years old (as of 2021) and lives in Japan. He still has a Space Spanner and he sent me the "missing knob" for mine. Yes, an American made knob sent from Japan. Thanks for the knob, Rob!
 


FURTHER READING

 
Lanny Conroy built a Space Spanner from scratch here.
Big Nick built a Space Spanner from scratch here.
Rich Post identifies a mystery regen radio. (Page 15) here.
Allied Radio catalogs can be found here.
Additional Allied Radio catalogs can be found here.
 
 

 
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