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Air King Tiny Bakelite Receiver
#1

Hello everyone,

 I recently bought at auction a very scruffy Air King Bakelite receiver as part of a lot which included a Model 40 Avo multimeter. Neither was going  . The chief merit  of the Air King and perhaps its main selling point was that its case is only 7 inches by 4 3/4 inches by 5 1/2 inches yet it contains a pleasingly sensitive though not specially powerful t.r.f. receiver.

As you will have gathered from the foregoing the Air King (an a.c.d.c. set ) is now a runner and there is a little story attached to that.
As you may know here in New Zealand our mains voltage, like the U.K. is 240 volts.
 But the Air King is ,I think ,from the U.S.A. running on 117 volts . Adding together the filament voltages of the 6C6 the 6D6 the 25L6  and the 25Z5 rectifier I get around  63 volts suggesting the set probably had a line cord of a suitable ohmage to drop the 117 volts to 63. 
But as found the set had only about two inches of three core  mains cord , in very perished condition, attached.Only two  of those wires,the red and the black ,were actually soldered to the radio, the black going to the switch and thence to the chassis and the red to a tag on the rectifier socket. The third (brown) wire went nowhere ,ending inside what remained of the cloth covering on the mains cord.I wondered if this brown wire was a remnant of the old resistance line cord but with only a couple of inches to measure I got no clear reading of its  resistance. I came to the conclusion that someone had used an ordinary piece of three core wire (very common here in N.Z. ) to get this set to go.
But how to make it go on our 240 volt mains? Stuffed inside the cabinet was a metal barretter tube reading 150 ohms  wired from the red mains wire to the start of the  filament  chain  at the 25Z5.

 Maybe this was how some enterprising person had got this set to go on our mains voltage. But the poor old barretter was obviously working hard getting rid of the heat. There is not much room in the cabinet anyway  and a barretter placed sideways above the valves already there must have  proved a bridge too far. Solution ? Drill  six  1/4 inch holes in the top of the bakelite cabinet. Still running hot? Drill several 1/16 inch holes in the metal  shell of the barretter ! 

So this was the condition of the set when I bought it - a scraggy bit of mains wire, a lovely little bakelite cabinet vandalized ,and an added in barretter which  had obviously run very hot . In order to bring some order to this mystery I disconnected  the barretter,added a new piece of two core flex in place of the red and black and ,after replacing various suspect caps ,  plugged the set in to the variac.

 I attached an aerial  and wound the variac up until the voltage across the 6D6 filament was exactly  6.3 volts whereupon the set burst into life!

The voltage at that point across where the red and black wires were connected was 65 volts.I have come to the conclusion that that is the correct voltage for this set and the line cord probably supplied that. Those of you in the U.S.A. who have more familiarity with sets using line cords will be able to tell me if I am correct here. I welcome your comments. Line cords are uncommon here in N.Z. I have read about them but never seen one . So I am curious to know what the original schematic for this set looked like which is the ultimate reason for my post. I have drawn the circuit out  but I would like to know the missing line cord details.

A kind person has given me an intact empty cabinet for this set and I also have what I believe to be an original wooden cabinet so restoration can proceed apace. Google searches for this set have proved inconclusive because I do not know the model number. If anyone can provide that I will be very grateful. Any help to locate the schematic would be useful too. Some where in the garage I have a suitable 65 volt transformer  which will allow me to run this set on our mains without the need of the variac so I have plenty to keep me occupied during our covid lockdown. Cheers everyone.
#2

Without any pictures of the radio in question, and of its chassis, it is impossible to tell you any more about that radio. Air King made a lot of different radios, and, being one of the lower priced sets, a number of them were "curtain burners," sets which used resistance cords.
#3

The Air King model 222 is a tiny regenerative bakelite set with your tube list and a "curtain burner." Since you have the right transformer, go with it.
#4

Here is a link to a site where you can input your tube line up, and see what radios used that line up. Knowing the manufacturer you can then look up the models which that manufacturer made using that line up, and find the one which matches your set the closest.  https://grillecloth.com/sylvania/tubelist.php   I have found this a useful place to start.
#5

This might get you close http://www.nostalgiaair.org/pagesbymodel...000379.pdf
The 43 tube is the same as the newer 25L6, it has the self centering base.

GL with your project!

When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!

Terry
#6

On the heater situation using a non polarized capacitor to replace the series resistor works well. No heat but sometimes size can be an issue. https://www.vintage-radio.com/repair-res...calcs.html

When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!

Terry
#7

Very special thanks to Rod B., Mike the Druid and Radioroslyn. You have been most helpful. I have been able to find the set both on Radio Museum and in Riders.It is ,as you say Rod,a Model 222. However it seems, though I'm no expert and haven't examined the r.f. side of it , not to be a regenerative set but in fact a simple t.r.f.
I really enjoy this phrase of yours "curtain burner ". I presume this came about from folk winding the line cord in a circle to reduce its length or did they get hot enough to in fact set fire to , or scorch anyway, any fabric nearby even if laid out straight ? So far as I am aware we did not use line cords here in N.Z. with our higher mains voltage.We do have numerous a.c. d.c. sets,especially later model Philips sets but these use large ceramic dropper resistors on the chassis.Most of our 30s and 40s sets here used transformers.Thanks again .
#8

A member of my group did a presentation on "curtain burners" suffer through a first few minutes here and see David's talk with illustrations......David starts at about 11 minutes in.

https://www.youtube.com/watch?v=Bs-mKnwLtLM&t=1867s

Good luck.

Paul

Tubetalk1
#9

Interesting video, Paul, but that person who's breathing heavy into their mike is REALLY annoying.
#10

David, I just found this link to a site where a guy used a non-polarized condenser to drop the voltage across the filaments of a radio with EXACTLY the same tube line up as yours. I have followed the guys site for years, since he has a lot of good information on the old Radiola radios, and my oldest tube set is a Radiola Senior. I also have a Radiola IIIA. This should help you solve your situation. https://www.radiolaguy.com/info/resistan...0cords.htm
One thing you may wish to be careful about. You may wish to avoid non-polarized ELECTROLYTIC condensers in this application because they are NOT rated for continuous AC use and this application will shorten their life. Mylar condensers of over 100VAC rating (better over 150VAC) are preferable for this application.
Here are some other interesting links you might find useful...
https://www.antiqueradios.com/forums/vie...hp?t=29083
https://radioether.blogspot.com/2008/02/...istor.html
https://radioether.blogspot.com/2008/02/...art-2.html




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