Center post on 9 pin and 7 pin miniature tube sockets

[currituckco]

This may be a dumb question, but why do some 7 pin miniature and 9 pin noval sockets have a center post? Is it just an extra lug for convenience or does it have some other special purpose? How is it usually used?

 

[electroking]

Hello,

It can indeed be used as a convenient tie point. Also, in some high-frequency
applications, it provides some shielding between the pins. An extra
shielding plate can be soldered to this post.

 

[Old1625]

While it could be used for nearly any tie point application the traditional use was for a local star grounding point. And, yes, sometimes shielding was used at that point, usually that the tube socket was located in a notch in a shield partition. Tube socket pins that were to be directly grounded were simply folded in and soldered there.

 

[currituckco]

Thanks!

 

[andy]

There are a few tubes that actually have a center pin, but I've never seen one used in audio.

 

[jrsh92]

I usually use it as a ground point. I have a 9 pin socket that looks like an 8 pin socket but instead of having the large stabilizing piece of plastic found on octal power tubes, it had another center pin-- not a center post as we're talking about here, but another pin. I have no idea why.

 

[Steve O]

There are a few tubes that actually have a center pin, but I've never seen one used in audio.

The 6C9 is one such tube. It's a dual RF tetrode and has ten pins in what looks like a std nine pin pkg. Heath and some other brands of low cost FM tuners used them in the front end. One tetrode was an RF amp and the other was a self oscillating mixer.