Dual grid and plate pins

MrCurwen · 21st October 2011, 08:45 PM

I've been curious about the pin configuration on my latest find, the 8025A. I haven't yet done anything with it, but I intend to drive ESL headphones with it.

http://www.trevick.com/john/wp-conte...025_RCA_00.jpg

The tube has filament connections on the base (including a center tap). The top two pins on the sides are both connected to the plate, and the bottom two both connected to the grid. Now this is a single triode envelope of course.

Why did they put in double connections? Especially since you have to have caps covering the pins even if you don't use them - I wouldn't leave a metal part uncovered with the plate potential on it. So no savings really. These tubes were meant primarily for HF operation, in radio equipment and possibly radar. Is there a HF reason for double pins? How does it work?

Aesthetically I like the buggers. Rugged looks, engineer's tubes. =)

Rod Coleman · 21st October 2011, 10:29 PM

For UHF valves, doubling up the pins reduces inductance. The internal wiring is very long in high frequency terms - and lowered inductance makes a big difference at the frequencies they were designed for.

For non-UHF use, you can cut the pins off, if they are in your way. Just be sure to use a method that does not break the tube. OR, remove the socket connexions.

MrCurwen · 21st October 2011, 10:38 PM

Ah, makes sense. Thanks.

Aesthetically I like the symmetry so it's ok!

21st October 2011, 08:45 PM	#1
MrCurwen diyAudio Member Join Date: Feb 2010	Dual grid and plate pins I've been curious about the pin configuration on my latest find, the 8025A. I haven't yet done anything with it, but I intend to drive ESL headphones with it. http://www.trevick.com/john/wp-conte...025_RCA_00.jpg The tube has filament connections on the base (including a center tap). The top two pins on the sides are both connected to the plate, and the bottom two both connected to the grid. Now this is a single triode envelope of course. Why did they put in double connections? Especially since you have to have caps covering the pins even if you don't use them - I wouldn't leave a metal part uncovered with the plate potential on it. So no savings really. These tubes were meant primarily for HF operation, in radio equipment and possibly radar. Is there a HF reason for double pins? How does it work? Aesthetically I like the buggers. Rugged looks, engineer's tubes. =)

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21st October 2011, 10:29 PM	#2
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	For UHF valves, doubling up the pins reduces inductance. The internal wiring is very long in high frequency terms - and lowered inductance makes a big difference at the frequencies they were designed for. For non-UHF use, you can cut the pins off, if they are in your way. Just be sure to use a method that does not break the tube. OR, remove the socket connexions.

21st October 2011, 10:38 PM	#3
MrCurwen diyAudio Member Join Date: Feb 2010	Ah, makes sense. Thanks. Aesthetically I like the symmetry so it's ok!

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