08-31-2021, 12:57 AM
Hi everyone,
Some of you may have read between the lines on my recent post about the Air King Model 222 and felt a vague disquiet.I mentioned that it seemed not to be very powerful and I suspect I now know why.
On first checking out this radio on the bench , as I mentioned. I had no schematic and only a scruffy bit of what we in N.Z. call "mains" cord .And there was this barretter in the mains line.And I am unfamiliar with a.c./d.c. sets.Furthermore I was , and am , very aware of the danger of fizzing the filaments of the two 25 volt tubes as these are rare in N.Z. and hard to replace .So the plan was to start from zero volts on the variac until I had the right voltage across the filaments of the valves.
So I reasoned that if I wired the variac one lead (the black )to the switch and thence to the chassis and the other (the red ) to pin 6 of the 25Z5 (the start of the filament chain) and also to the anode of the 25Z4 and turned up the variac till I had 6.3 volts across the 6D6 I should have 25 volts across the 25Z5 and 25 volts across the 25L6 filaments and no more .Which I did!
Does all this make sense?
At that point I measured the voltage from the variac across the two "mains "leads ( the red and the black) and found it to be 65 volts. And the radio played at that voltage.From this I falsely concluded that the right voltage for this set was 65 volts and it was the job of the line cord to reduce the 117 voltage to 65 to make the radio run. I can see you all shaking your heads and saying "Take another look at the schematic , David".
Yes, there has already been an "Aha! " moment. The "hot"117 volt lead should go to the anode of the 25Z5 and THEN to the line cord and then to pin 6 of the 25Z5 and the rest of the filament chain.This would give a higher H.T. voltage and probably a higher output.And the correct voltage across all the filaments.
The blushes are fading now and I am working out how to get this set to go on our 240 volt mains. I have several 240 / 110 volt transformers and,as mentioned, one 240 /65 volt transformer so I think I have the problem solved with the transformers hidden in a box and four wires from the box to the set we will be in business.
It pays to take your time in this radio fixing game.
Cheers everyone.
Some of you may have read between the lines on my recent post about the Air King Model 222 and felt a vague disquiet.I mentioned that it seemed not to be very powerful and I suspect I now know why.
On first checking out this radio on the bench , as I mentioned. I had no schematic and only a scruffy bit of what we in N.Z. call "mains" cord .And there was this barretter in the mains line.And I am unfamiliar with a.c./d.c. sets.Furthermore I was , and am , very aware of the danger of fizzing the filaments of the two 25 volt tubes as these are rare in N.Z. and hard to replace .So the plan was to start from zero volts on the variac until I had the right voltage across the filaments of the valves.
So I reasoned that if I wired the variac one lead (the black )to the switch and thence to the chassis and the other (the red ) to pin 6 of the 25Z5 (the start of the filament chain) and also to the anode of the 25Z4 and turned up the variac till I had 6.3 volts across the 6D6 I should have 25 volts across the 25Z5 and 25 volts across the 25L6 filaments and no more .Which I did!
Does all this make sense?
At that point I measured the voltage from the variac across the two "mains "leads ( the red and the black) and found it to be 65 volts. And the radio played at that voltage.From this I falsely concluded that the right voltage for this set was 65 volts and it was the job of the line cord to reduce the 117 voltage to 65 to make the radio run. I can see you all shaking your heads and saying "Take another look at the schematic , David".
Yes, there has already been an "Aha! " moment. The "hot"117 volt lead should go to the anode of the 25Z5 and THEN to the line cord and then to pin 6 of the 25Z5 and the rest of the filament chain.This would give a higher H.T. voltage and probably a higher output.And the correct voltage across all the filaments.
The blushes are fading now and I am working out how to get this set to go on our 240 volt mains. I have several 240 / 110 volt transformers and,as mentioned, one 240 /65 volt transformer so I think I have the problem solved with the transformers hidden in a box and four wires from the box to the set we will be in business.
It pays to take your time in this radio fixing game.
Cheers everyone.
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