08-17-2021, 09:05 PM
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.
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.
