Knight | Space Spanner

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Actor Morgan Freeman at the dials of a Space Spanner when he was in the Air Force around 1956.
Click here to see a rotated version of the photo.


These headphones belonged to James Kasper and came with the Space Spanner from ebay. Allied sold an antenna and a pair of headphones to augment the radio. I was hoping these would be the ones in the catalog.

Unfortunately, this headset doesn't even appear in the catalog.
These are CANNON-BALL "Empires."
Allied carried
CANNON-BALL "Master" and "Chief" headphones in 1957 and '58, but not "Empire."
These are the Allied brand headphones sold in the 1957 catalog next to the picture of the Space Spanner. They were $2 and rated at 2000 ohms. An upgrade to a CANNON-BALL "Chief" or "Master" would cost 22 or 44 more.


Why do so many Space Spanners have a missing knob on the antenna tune control? (pictures from the Internet)
One of the manuals shows the knob missing, but the parts list shows FOUR knobs were included.
On the left is a photo of the antenna tune control before I cleaned the front panel. From the mark on the panel, it is obvious that it once had a knob, and the knob came into contact with the front panel. On the right is the answer to the mystery, one of the greatest mysteries of the 20th Century. It's on par with Billy Shepherd replacing Paul McCartney.

The mystery has been solved! See that backed out set screw in the picture on the right? It's the answer.

The instructions in the manual say to remove the set screw. The reason for this is that as you tune the antenna, the shaft on the control moves inward or outward. A knob with a set screw will prevent the control from moving inward when the knob comes into contact with the front panel.

Without the set screw, the knob could come off if the shaft on the control was recessed too far. That is the answer to the mystery. The knobs are missing because THEY FELL OFF.

There is no reason why anyone should open the control so far that the knob would fall off, but it was done. One person told me he closed it so tightly he stripped the threads. Some people boast they built a Space Spanner when they were twelve years old. Maybe so, but some of them didn't understand the function of the antenna tune capacitor when they were twelve.

At any rate, Allied didn't sell a replacement knob! That makes these knobs very rare. If you want to buy a "Smooth-On" molding kit and mold them yourself, the starter kit and the resin will set you back $50.

Can you actually "GENTLY force" something? "I'm going to GENTLY force your hand into the garbage disposal." "I'm going to GENTLY force you to give me all your money." "I'm going to GENTLY force this knife into your back"

It doesn't seem to work in all situations.


The antenna tune capacitor is not perpendicular to the front panel. It's because of the "ears" on either side, which are the electrical connections. One comes from the front and the other comes from the back. I tried bending them, but they just flattened out again as the screws were tightened.

Fortunately, there is no electrical connection with the shaft, so if the shaft comes into contact with the front panel it won't affect the radio. However, we can't have this, the situation is must be resolved at all costs!
A quick fix was to shim it with a washer on one side.
Warning; The ceramic standoffs are fragile and can be ruined by over-tightening the screws.


The big resistor in the filament string (R-11) gets hot. Resistor R-9 is in contact with R-11. The instructions don't describe anything different about soldering in R-9, but the drawing does. It shows R-9 some distance away from R-11.

In ten minutes, R-11 reached a temperature of 192F. Is that a problem? When R-9 was heated by R-11 the value went down by two ohms. It's connected to the cathode of the 50C5 audio output tube. Considering the schematic calls for a 180Ω resistor (10% tolerance) but R-9 actually tests at 209Ω. I don't think it makes any difference. It already exceeds the 10% tolerance by 3 percent anyway.

R-11 was pushed closer to the chassis to put some empty space between it and R-9.


The Space Spanner had a short life of seven years. In 1959, Knight added the Span Master to its catalog of kits. It cost more but had sleek styling and two additional bands. It also sported a "fine regen" control for precision adjustment. This was serious competition.

In 1963 the Knight Star Roamer kit appeared. The Star Roamer was a Superheterodyne radio and had many advantages over the Space Spanner and Span Master.  It also had three times as many parts and a price tag to match. In 1963 the Space Spanner cost $18.95. The Star Roamer cost $39.95. In 2020 dollars that's $160 for the Space Spanner and $338 for the Star Roamer.

In 1964 the Space Spanner disappeared from the Allied catalog. 1968 was the last year for the Span Master. In 1970 the Span Master II was offered, but it wasn't a regen radio. The price was $29.95

Note: These are "entry level" radio kits. You could always spend $500.00 to $1000.00 on a communication receiver if you had the money. See the link to the catalogs at the bottom of this page.

By the way, I paid about $160 for the Space Spanner, so I got it at the 1963 price! (Adjusted for inflation, of course.) The worth of these radios barely keeps up with inflation, but the headphones I got with the radio have doubled in value.

Space Spanner VS 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 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.

Archer Globe Patrol in homemade wooden cabinet.

Two other similar radios appeared in the 1960's. The Archer Globe Patrol sold by Radio Shack and a rare clone made by Burstein-Applebee. Like the KT-135, both had four bands. They all had vinyl 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.


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).

I've also noticed that when I connect a double triode in parallel (mu remains the same, but gm is doubled, rp is halved), it works better as a regen detector. The 6J6 in parallel makes a fine triode detector.

One tube I'd like to try in a regen is the 12B4, a triode intended for audio output. Rp = just 1K. Should make an excellent detector.

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 70 years old (as of 2019) 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!


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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