01-26-2009, 01:03 AM
One cute way to cut the top off of the tube is to wind one turn of nichrome wire around the glass envelope of the tube. Apply a current through it enough to make it glow a good red heat. The concentration in the glass will cause the glass to crack in the line of the heater wire, and you have it "cut". They do this on cathode ray tubes when they cut off the old electron gun, preparatory to welding on a new one.
I'm a little amused by this thread. It's really the reverse of what we did during WW II. One "for instance" was the total unavailability of the 12SA7 for the duration of the war. Somewhere along the way, someone discovered that the 14Q7 is a Loktal 12SA7. It was the practice to make an adapter out of a discarded octal tube base, make the connections to a Loktal socket, and plug the loktal tube into the adapter, and the old base into the socket.
I've found that Loktal tubes have been easy to find, to the extent that I've found boxes full of them at swap meets. Nobody seems to want them, and often, they go begging.
The service shops never did like Loktals, because of the hazard of breaking sockets. Indeed, I once found a nice 42-1010 Philco in a furniture store, with all the tubes gone, and a few broken Loktal sockets. I bought it for 5 bucks, and the dealer almost kissed my feet for buying it. Sure, the replacement of sockets will some day be a bt of a job, but it will get me a nice radio. I have plenty of tubes for it, too.
One thing about Loktal tubes. Their construction was new and innovative, and it was soon discovered that they performed far better at high frequencies than Octal based tubes. Loktals would logically be just the ticket for television tuners in the 1939 sets, but for RCA to use Loktal tubes (a Sylvania development), would be like a Rabbi having a ham sandwich. The RCA 12 inch prewar set I have uses a 6J5 oscillator in the front end, but a 7A4 would surely have made a better choice. (An XXL, even?)
I'm a little amused by this thread. It's really the reverse of what we did during WW II. One "for instance" was the total unavailability of the 12SA7 for the duration of the war. Somewhere along the way, someone discovered that the 14Q7 is a Loktal 12SA7. It was the practice to make an adapter out of a discarded octal tube base, make the connections to a Loktal socket, and plug the loktal tube into the adapter, and the old base into the socket.
I've found that Loktal tubes have been easy to find, to the extent that I've found boxes full of them at swap meets. Nobody seems to want them, and often, they go begging.
The service shops never did like Loktals, because of the hazard of breaking sockets. Indeed, I once found a nice 42-1010 Philco in a furniture store, with all the tubes gone, and a few broken Loktal sockets. I bought it for 5 bucks, and the dealer almost kissed my feet for buying it. Sure, the replacement of sockets will some day be a bt of a job, but it will get me a nice radio. I have plenty of tubes for it, too.
One thing about Loktal tubes. Their construction was new and innovative, and it was soon discovered that they performed far better at high frequencies than Octal based tubes. Loktals would logically be just the ticket for television tuners in the 1939 sets, but for RCA to use Loktal tubes (a Sylvania development), would be like a Rabbi having a ham sandwich. The RCA 12 inch prewar set I have uses a 6J5 oscillator in the front end, but a 7A4 would surely have made a better choice. (An XXL, even?)
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