[Drake] Sweep tube finals in Drake TR3

[John King]

I experienced something strange upon changing final tubes in my TR3.

I am working on my TR3 and have the receive section working fairly well, but the transmit section needs attention. I purchased three 12JB6A tubes that are NOS and appear to be RCA even though the logos are mostly worn off.

I removed the three Sylvanias which were taller than the replacement tubes and replaced the Sylvanias. When I turned the TR3 on, the fuse blew. I replaced the fuse three times and the fuse blew each time. Thinking the power supply might have developed a short of some sort, I changed the power supply to another of my four drake power supplies and the TR3 still blew the fuse when it was switched on.

I removed the final replacement tubes and replaced the OLD Sylvania tubes and the TR3 has been on about 16 hours and is still on and receiving.

Has anyone found that a certain brand of sweep tube might be so internally wired that it will not work as a transmitting tube in a TR3 due to the hookup of the elements in the tube?

The benefit of your knowledge and experience will be appreciated. 73 and Happy New Year, John, K5PGW