Most modern electronics are going to be dead within a decade. Modern electrolytic capacitors are good for a few thousand hours at best. But I have turned on many a 70 year old radios and they play just fine. The 1941 Zenith console here in the living room has its original electrolytics in it, now 72 yrs old and still perking. The older the better, actually-- that Radiola has paper capacitors, which might be slightly leaky, but still work just fine 88 years since they left the factory. The audio transformers sometimes go open, as they have like 50 Henrys, bazillions of turns of #42 wire in them, which is prone to corrode and fail.
Sorry Mr C but IMHO that thing is an ugly piece of junk! Only its mother would love it!
Now don't get me wrong, it fascinating to have such a great teardown, and thanks to the other commenters for the schematic and great circuit analysis (leaky grids and control of volume by heater current indeed!)
But I have to say that such a monstrosity would have no place in my home, maybe it could be converted into a graden bird house if the birds aren't so concerned about their street cred living in such a hovel.
I remember doing a restoration on a similar beast: the best thing about the job was the smell of ancient flux when you finally get the old solder to melt. It smelt like cracking open a pharaoh's tomb :-)
Very nice, Caleb! I presume you have not fired it up? It's so simple it shouldn't take much to get it going, you should be able to build a power supply to supply all those voltages. You could use a battery powered amp for the speaker if you can't find a suitable speaker or headphones. Or I daresay you could make do with a mains-6v transformer and put a small 8R speaker on the 6V side - frequency response wouldn't be great but hey, it's only AM. Of course if any of the tubes don't work you'd probably have a problem finding replacements....
Elektor Magazine has a monthy column "Retronics" where they do similar "teardowns" of old electronics - mainly test equipment. It's one of my favourite parts of the magazine.
I cut my teeth on valve radios (thought not this old) and remember them with great affection - especially things like Magic Eye tuning indicators...
Caleb, I was recently given an old set of Audel books, copyrighted 1917 to 1923. They include some sections on electronics and radio, and a great deal on electrical power in general, both large and small. It is indeed interesting to observe how things were done back when labor was cheaper than materials. The effort required to add an outlet to a room in a house was a whole lot more than it is today. And a lot of the explanations for how electrical things work are interesting inn that they assume no previous exposeure to electrical anything. Really a fun read book set .
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