Knight | Space Spanner

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A third Space Spanner
 
A Space Spanner went up on ebay in February 2021. The front panel didn't look too bad, so I grabbed it just to get the panel.
 
A comparison of the two front panels.
The second panel (on the right) didn't look new, but it sure looked better,

 
 
 
 
It had a Mullard 12AT7 which I immediately took to replace the Canadian GE that was in Tim's radio.
The 50C5 was labeled "Made for Knight by RCA," so that was swapped too. The original had no markings on it.

 
 
 
 
 
The grommets on Tim's speaker disintegrated when I took the screws out. They were replaced with rubber O rings.

 
Both cabinets are in very nice condition.
 
I've read that these cabinets were made by a luggage company in Chicago.

 
 
Kinght Space Spanner
Tim's radio with the replacement front panel and the proper screws.
 
Very little panel oxidation, though you can see some if the light is right. At least it's not gold colored.
 

 
 
Here's the Space Spanner from the February ebay auction with the front panel off. The metal capacitor can in the back isn't original to the radio. At some point in time the filter capacitors failed and they were replaced with the ones in the can. This wasn't a good idea, the metal can is the negative side of the capacitors and it's connected right to the chassis. I have to admit it does look cool.

Connecting the negative side of the filter capacitors to the chassis also connects one side of the AC cord to the chassis. You have a 50-50 chance of being seriously shocked by touching the chassis, depending on how the unpolarized plug is inserted into the AC outlet. This is a "hot chassis." Man, I coulda been zapped with this thing! I wish I had some potential, but not that kind.

The dickens, you say. It was in a wooden cabinet, you say. Yes, but the front panel is metal!
 
From the rear, after the front panel was swapped. That capacitor really makes the radio look good. I wish they came that way.
 
120 volts AC straight from the outlet to the front panel.
 
Under the chassis. It seems the capacitors in the can failed and someone added some new ones. They're floating in the air and have 130 volts on the bare wires. The black wire isn't supposed to be there. The blue wire is connected to one of the tabs on the can, so the old cap in the can is still in the circuit, even though a new one has been added.

The black wire is connecting the capacitors to the chassis. Whoever did this didn't realize the metal can was supposed to be isolated and just re-made the electrical connection when it was cut out of the circuit. 
Click on the photo for a larger version.
 
I got rid of the black wire and the exposed leads, but the capacitors are still floating in the air.

 
 
I wish I had found this one before I bought the one from Canada. I would have just rewired half of it. Oh well. I put it back up on ebay, along with Tim's box and manual, for $60, half of what I paid for it. I figured the knobs and the tuning capacitors were worth $60.

It was purchased by a guy named William Gann, who previously did an excellent job restoring a Lafayette KT-135. (It's at the bottom of Page 6 of the KT-135 pages on this site.) When he saw that the Post Office soaked me $56 on the shipping, he sent me another $40!

 
Old and new styles. Same radio, different paint.
 

 

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 Space Spanner sported a two tone front panel in 1959, the KT-135 followed in 1961.

 
 
 
 
  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.

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 Grasing. 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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