Another tube radio

Magnetmaz · 11th March 2003, 02:37 PM

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:

Magnetmaz · 11th March 2003, 02:39 PM

back

James D. · 11th March 2003, 03:54 PM

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

bournville · 11th March 2003, 03:57 PM

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!

bournville · 11th March 2003, 04:02 PM

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..)

James D. · 11th March 2003, 04:33 PM

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

Morse · 11th March 2003, 04:33 PM

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

bournville · 11th March 2003, 07:01 PM

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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11th March 2003, 03:54 PM	#3
James D. diyAudio Member Join Date: Nov 2002 Location: North Herts, UK	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

11th March 2003, 03:57 PM	#4
bournville diyAudio Member Join Date: Feb 2003 Location: Birmingham, UK	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!

11th March 2003, 04:02 PM	#5
bournville diyAudio Member Join Date: Feb 2003 Location: Birmingham, UK	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..)

11th March 2003, 04:33 PM	#6
James D. diyAudio Member Join Date: Nov 2002 Location: North Herts, UK	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

11th March 2003, 04:33 PM	#7
Morse diyAudio Member Join Date: Jan 2003 Location: US for now.....	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

11th March 2003, 07:01 PM	#8
bournville diyAudio Member Join Date: Feb 2003 Location: Birmingham, UK	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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