10-31-2014, 12:00 AM
I rather resent the current fashion of using "purist" as a pejorative, as though to denounce or belittle sound preservation and workmanlike restoration techniques. It's been my experience that it often easier to put a radio, or anything, back to original, or at least start over from scratch, then it is to try to get into the head of whoever modified the set. From what I can see they left all of the original coils in place, the only thing missing is the original output transformer which was supposedly mounted under the chassis, other then the tube shield bases being removed from the 1N7G and 1A7G sockets. It would not take that much to convert it back into a battery radio again, if you forget about the Philco style tube shields, although you could probably find an unmolested chassis to restore instead.
The question is did this thing ever work after they did all these mods to it, and if it did how well did it work? I've never actually seen a farm battery radio converted to AC operation using AC tubes, that was successful. Most I've seen are borderline hack jobs, to outright hack jobs. I think that most people who wanted to run a battery set on AC either bought a power supply like a Sears Power-Shiftr or an Electro where you could plug your battery cables into the supply, or they built a home brew one. I have a plan for a home brew one out of a Radio Craft/Radio Electronics magazine from the 1940s, although there are obviously more modern designs now. This isn't to say that it could not be done properly, but I would pretty much ignore whatever this last guy did to it and treat it like a clean slate. To make everything work properly you would have to change more then just the B+ circuitry and the filament wiring from parallel to series string, things like resistor values and biasing would need to be changed, for example. I'm also not sure if an oscillator coil designed for use with a 1A7G would work with a 12SA7, the antenna coil would be fine, and the IF transformers I think would be the same.
I don't really know how one would get away with just soldering a tube socket in place, unless it had metal ears that they then soldered to the chassis, if it was held in place by attempting to solder the socket tie points to the chassis then they were shaking hands with danger doing so with a rectifier tube. What do we normally have with a 35Z5 or 35Z3? Well we have the hot side of the AC power line going to one end of the tube heater and also to the plate pin, if that socket decides to shift, and one of those pins touches the chassis, look out! So I would get a socket that does have mounting ears and rivet or mount it in with machine screws and nuts, or find one of the types that uses a locking ring, which are harder to find. I'm sure that someone here could provide you with either type, at least an octal one.
Regards
Arran
The question is did this thing ever work after they did all these mods to it, and if it did how well did it work? I've never actually seen a farm battery radio converted to AC operation using AC tubes, that was successful. Most I've seen are borderline hack jobs, to outright hack jobs. I think that most people who wanted to run a battery set on AC either bought a power supply like a Sears Power-Shiftr or an Electro where you could plug your battery cables into the supply, or they built a home brew one. I have a plan for a home brew one out of a Radio Craft/Radio Electronics magazine from the 1940s, although there are obviously more modern designs now. This isn't to say that it could not be done properly, but I would pretty much ignore whatever this last guy did to it and treat it like a clean slate. To make everything work properly you would have to change more then just the B+ circuitry and the filament wiring from parallel to series string, things like resistor values and biasing would need to be changed, for example. I'm also not sure if an oscillator coil designed for use with a 1A7G would work with a 12SA7, the antenna coil would be fine, and the IF transformers I think would be the same.
I don't really know how one would get away with just soldering a tube socket in place, unless it had metal ears that they then soldered to the chassis, if it was held in place by attempting to solder the socket tie points to the chassis then they were shaking hands with danger doing so with a rectifier tube. What do we normally have with a 35Z5 or 35Z3? Well we have the hot side of the AC power line going to one end of the tube heater and also to the plate pin, if that socket decides to shift, and one of those pins touches the chassis, look out! So I would get a socket that does have mounting ears and rivet or mount it in with machine screws and nuts, or find one of the types that uses a locking ring, which are harder to find. I'm sure that someone here could provide you with either type, at least an octal one.
Regards
Arran
