Tube mod. in 116B - Printable Version

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+--- Thread: Tube mod. in 116B (/showthread.php?tid=2489)

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Tube mod. in 116B - don'tdomelikethat - 07-03-2010

I'm beginning restoration on my 116B. At some point, someone subbed a metal 6J7 tube for the type 77 first detector tube. The tube socket was replaced. I looked in my tube substitution guides, and these tubes are not direct replacements for each other. However, I looked in my RCA tube manual, copyrighted 1940, and in the listing for the type 77, there is one small sentence that states, "for detector operation, see Type 6J7." Apparently the person who did the modification read this sentence himself, and thought this tube would work because of this. While I know the 6J7 is not original, especially since Philco would have never used a metal tube, I wonder if leaving this tube hurts or helps operation. I am willing to buy a new tube socket, and change it back to a 77, so that it's original electronically. I just wonder how well the 6J7 worked in the set after it was first modified years ago... maybe during World war 2 when some tubes were hard to get. Any thoughts?

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Re: Tube mod. in 116B - Ron Ramirez - 07-04-2010

Hi

The 6J7 is electrically very, very similar to type 77.

http://www.nj7p.org/Tube4.php?tube=6J7
http://www.nj7p.org/Tube4.php?tube=77

Look at the figures for a class A amplifier with 250 volts on the plate and 100 volts on the screen - the figures are almost the same.

I think I would probably reinstall a six pin socket and a 77 tube, but if you leave the 6J7 no harm will occur and the radio should perform as original.

If you do leave the octal socket in place, be sure to ground pin 1 of that socket.

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