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Old 11th March 2003, 02:37 PM   #1
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Default Another tube radio

My uncle gave me his 1936 Sears Silvertone radio this past weekend, so i'm restoring it currently.

3 of its tubes have those plugs attached to the top of them. My question is what were those for? Why did tubes have a plug coming out of the top, and couldn't this have been moved to another pin on the bottom?

pics of the radio so you can see what i'm working on:
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Old 11th March 2003, 02:39 PM   #2
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Old 11th March 2003, 03:54 PM   #3
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Nice radio!

The top caps are usually for the anode. They remove the B+ connection from the base and so ease the insulator requirements and layout constraints at the base of the valves.

ciao

James
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Old 11th March 2003, 03:57 PM   #4
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Nice looking set

In answer to the first part of the question, the top caps for the frequency changer, IF amplifier and the first audio amplifier (usually a double diode triode) are the signal grid connections.

I don't really know that answer to the second part - I'd hazard a guess that it was due to the state of the construction technology available at the time which made it easier to use top caps, and possibly it was an attempt to avoid instability to have the signal grid well separated from the connections for the other parts of the tube.

With a frequency changer tube, which normally was a triode-hexode, triode-heptode or octode tube, you could run out of pins on the bottom of the tube anyway for all the connections you need!
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Old 11th March 2003, 04:02 PM   #5
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James,

Just seen your post. Usually its just output tubes which has the top caps for the anode, for signal amplifiers at IF and AF, and frequency changes the top cap is for the signal grid (see specs for tubes such as the 6K8, 6K7, 6Q7 etc..)
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Old 11th March 2003, 04:33 PM   #6
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Hi Bournville.

Thanks for your note. I had forgotten all about signal grid at top!

Amazing how much one forgets over 25 years of not using part of ones memory...

I need to start looking at rf TX and RX designs again Great!!!

ciao

James
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Old 11th March 2003, 04:33 PM   #7
Morse is offline Morse  United States
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That's one terrific looking radio, Magnetmaz!!

Three cheers to you for taking the time to restore it, too! I always feel ill when I hear of someone trashing a lovely old radio like that, so it's good to see that there are people like you taking care of the classics.....

All the best,
Morse
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Old 11th March 2003, 07:01 PM   #8
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Magnetmaz,

In case you haven't seen them yet, there are some schematics for old Sears sets located at:

http://www.nostalgiaair.org/Nostalgi.../schem_SRC.htm


With a bit of luck your set will be amongst them.
Good luck with the restoration.
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