Thomas
http://www.nostalgiaair.org/Resources/397/M0023397.htm
http://www.nostalgiaair.org/Resources/276/M0011276.htm
BR,
Ken
The method mentioned above will probably give you the most compact and reliable results, but may not be the method you are looking for due to changing the power transformer (to some, changing this transformer might reduce the value of the set....to others, being able to operate an obsolete 32 volt radio from 110 volts would be terrific).
Another method would be to leave in the 12 volt tubes (and leave the 12A5 wired for 12 volts). Connect two of the 6 volt tubes in series, and connect a 2 ohm 10 watt resistor in series with the remaining 6 volt tube. Connect the radio to a 12 volt DC source, such as a 12 volt battery charger capable of 8 amperes or more. The problem with this is that the power transformer is designed to be fed 32 volts. Perhaps removing some of the chokes between the vibrator and the transformer may help. With these gone, instead of condensers across the vibrator, it'll be necessary to install 100 ohm resistors, one from each transformer primary end to its center tap (two total). The voltage at the transformer secondary will determine whether or not the correct voltage is being sent to the transformer primary. There should be about 225 volts at the rectifier plates when using the original power transformer. Another problem is powering the field coil, as it won't be receiving 32 volts....just 12 volts. Wiring the field in series with B+ (and then removing the original choke from B+) may power it properly. I could do a conversion like this and perhaps have it work quite well, but it would take a lot of trial and error.
The third method is to build a 32 volt DC power supply capable of about 4 amperes. You could possibly use two 24 volt transformers with their secondaries wired in series and in phase (check total AC voltage so that it reads 48 volts). Send through a full wave bridge rectifier capable of the amperage. Filter with a 1000 MFD 75 or 100 volt condenser (3000 MFD would be better. Don't know if it is easy to obtain either value in the voltages listed above...they usually come rated for 50 volts). Send through an appropriate resistor or choke capable of handling the current. The resistor would probably have to be capable of 20 or more watts (paralleling resistors may work). The output should be filtered with another electrolytic like that mentioned above. The output should be 32 volts when loaded by the radio. Filter condensers like those mentioned above might not be necessary (which may prove to be an asset if you cannot locate any). I have found that vibrators operate quite well from the full wave rectification sent out by most battery chargers (which isn't filtered). The B circuit in your radio has its own filter, and so filtering the DC going into your radio will have no effect here. It may have an effect on the field coil of the speaker (excessive hum). If you find that you can get by without the electrolytics, just be sure that 32 volts is available to your radio when the power supply is loaded by your radio. Change resistances in the 32 volt supply appropriately.
Thomas
Regarding converting the radio to 12 volts (probably the least definite method), all of the tubes should be wired in parallel. Two of the 6 volt tubes should be wired in series with eachother, and in parallel with the rest. The remaining 6 volt tube should be wired in series with a 2 ohm resistor, and this should be wired in parallel with everything else.
Thomas
I Thought I might add to this as I rebuilt one of these Airline sets about ten years ago. I bought two 32 volt farm sets from the same dealer a year apart and should have known better. Both times he told me he plugged the sets into 120 and said all they did was buzz loudly. Fortunately, only tubes were burned out but in both cases the irreplacable speaker field coils were OK. In both sets they were hooked across the 32 volt line cord.
I was fascinated by the design of the Airline set and decided to get it going. Only the 12A5 and one 12Z3 were blown. I built a 32 volt power supply using a free power transformer from a video game. I had spent many years in the coin game business and when games came to the end of their money making life, they were gutted and a new board and power supply were put in making them into a new game. We had easily a hundred power transformers out of Midway games: Pacman, Ms Pacman, Galaxian and Galaga which used on-board power supplies with AC going into the logic board. These transformers had a high current 14 volt winding and several other heavy windings which could be series connected to get 32 volts with at least 10 amps. Using surplus computer grade caps available cheap at hamfests and a 25 amp bridge rectifier, I could reliably power my 32 volt sets. The second set was a Lafayette low B+ voltage design with 32 volts on the plates using push-pull 48's in the output which worked fine but the Airline had an annoying buzz that was difficult to find at first. It turned out to be diode switching noise from the bridge rectifier. I found putting a .1 mfd across the ac input to the bridge totally removed the buzz and the set plays perfect now.
I see a guy on eBay from time to time selling 32 volt switching supplies advertised to power farm radios but I had little luck using switcher supplies as they radiate noise and more or less cover up the stations you can hear. I never tried one of his so I can't say for sure how they would work.
If you know of a company in your area that refurbishes old games, you could probably get a transformer for next to nothing. My old company ended up throwing them away after I left.
Fred R