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Old 9th July 2004, 06:43 PM   #1
6SN7GT is offline 6SN7GT  United Kingdom
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Default why multi pins ?

Simple question from a tyro.

Why do some valves have more than one pin for a connection.
For example:-

I'm going to use 6C45pi in cascode for my RIAA phono first stage.
They have 3 pins connected to the cathode and 2 pins connected to the grid.
Why?

As Cag is important here and I only really need one pin, what do I do with the other pins?

Sorry if this sounds dumb to experienced members, I've searched the web but didn't find an answer.
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Old 9th July 2004, 08:11 PM   #2
Colt45 is offline Colt45  Serbia
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well, they started off with a standard envelope,

since all pins werent req'd, they doubled some up to make it more versatile, i guess.

oh yeah, just leave the other pins floating
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Old 9th July 2004, 08:14 PM   #3
EC8010 is offline EC8010  United Kingdom
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Valves designed for use at HF and UHF have electrodes going to more than one pin in order that, no matter what the layout, short wires can be used to each electrode. At UHF, a short bit of wire is an inductor. I've never worried about unused pins, although some people suggest that a grid-stopper resistor to each grid pin, and then connected together at the far end, allows a smaller total value of grid-stopper, reducing noise.
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Old 9th July 2004, 08:31 PM   #4
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Multiple grid stoppers, arranged in a "cone", are in order when using a 5842 in common cathode circuits. The 5842 was intended for use as a grounded grid high RF amp and the multiple grid connections help control unwanted reactive effects. With its high gm, the 5842 will oscillate without stoppers "everywhere".

IMO, it pays to look at the duty any type was originally intended for, as much can be learned. Many of the small signal types used in HIFI audio circuits were originally intended to be used in RF circuits. The EF86 pentode is 1 of the few small signal types developed (Mullard) for HIFI service.
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Old 9th July 2004, 10:28 PM   #5
dhaen is offline dhaen  Europe
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All the above and:
Glass based valves use the pins for mechanical support of the electrode structure. More supports = more rugged and lower microphony.
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Old 9th July 2004, 10:40 PM   #6
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In some cases they appear connected but are actually NC. Example: I have a few Magnavox 6V6s that are connected as such but they don't come out to the pins on the base.

Tim
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Old 9th July 2004, 11:34 PM   #7
dhaen is offline dhaen  Europe
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Yes Tim, I've seen that before too.
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Old 9th July 2004, 11:37 PM   #8
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Hi,

Quote:
In some cases they appear connected but are actually NC.
Not sure what's meant here....
Is it that the pinout diagram shows those pins as connected but in reality they're not and vice versa?

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Old 10th July 2004, 01:44 AM   #9
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Basing diagram is..erm... I don't remember what it is. Whatever NC or IC pins. I mean the wires go to the button base inside but aren't led out to the phenolic base, though you can't see because 1. all the pins are there and 2. it's notoriously difficult to see the actual bonding between base pins and where they pass through the glass.

Tim
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Old 10th July 2004, 01:46 PM   #10
6SN7GT is offline 6SN7GT  United Kingdom
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Wow!, many thanks for all the replies.

It seems I didn't ask a daft question after all

OK, so grid stoppers are a good idea, and I agree.

So the followup question is:

as the 6C45pi will be used for *audio* duties, is there any reason to just not join cathode pins together, and more importantly, join the grid pins together and use a single grid stopper?

The R term is way bigger than C or L for parasitic oscillations, so joining grid pins to a common stopper should suffice ?

Just testing the waters here
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