EL84 Free Pins As Tie Points?

[rp]

Can the terminals, 1, 6, 8, be used as tie points for the screen grid and swamper resistors Fender style. I've never seen it on EL84s, and the datasheet states IC (internal connection) not NC (no connection) which is why I never tried it in the past. But now I can ask you all.

[sluckey]

I would not do it. I have two pair of EL84s that have pin 1 internally connected to pin 2. I have others that have no connection between those pins.

You can find plenty of info on this using Google.

[rp]

So, when I see NC then I can assume the manufactures respect that - like the 6L6, but if I see IC it may or may not be connected somewhere and I must assume it is. Glad my default is to just do what I've seen others do.

[Smokebreak]

I happen to be doing some 7868s right now that has no available tie points, so i like to put down a 3 term strip. That covers both grids and the cathode sense. Boom.

[R.G.]

I would put it another way. On many ICs the term "NC" may be active or passive. Passive NC means "we didn't connect this to anything inside, so whatever you do is OK. It's just an empty pin. Active NC means "you MUST NOT connect anything to this pin, as we have used it for nefarious purposes of our own".

I've also seen "Internal Connection" as meaning "we used this as a convenient tie point or place to put a test signal or some such" so using it for external signals would be really, really inadvisable.

With the paucity of info about what really is inside the glass envelope, I would advise to suspect that any different tube even with the right type number might just have an active rather than passive "NC". You might have to put another manufacturer's version of the same tube number that isn't **exactly** the same inside in the same socket.

[BLT]

I've seen it used in certain instances where Dr. Z, Mike Zaite has used it in his builds. I've tried with some success. Here's an image from one of M Fowler's builds.

[pdf64]

I think some el84 manufacturer's info describes pin 1 as 'internal connection'.
My 60s JMI AC30 had links between terminals 1 (NC) and 2 (g1) of its el84 sockets, with the grid stoppers being connected to terminal 1, presumably because it's a bit closer to the terminal strip used for the power tube common stuff (grid stoppers between terminal strip and el84 sockets terminal 1).
The links never caused a problem but I removed it a couple of years ago, just in case.

[rp]

I was convinced at Sluckey's post, no way I'm doing it, even if it was 1965, but with all the post commie EL84s out there there's even more variability and unknowns. Strange about the Vox, maybe the Brit made EL84s subscribed to a common standard.

[Masco]

7189A's have pins 1&2 tied. 7189's do not.

[teemuk]

I would not do it.

First, I think it's not good design practice to begin with (given wide variety of tubes that likely get plugged into the socket), and secondly, I don't remember all the details, but I do remember reading threads about issues with amps where manufacturers took a liberty to use "N.C." pins as convenient component mounting terminals, which pretty much highlights the point of not being good design practice to do so...

[M Fowler]

My amps and tubes are going strong after about 3-4 years I'll let you know if or when a EL84 tube causes major problems.

I don't usually use extra tube socket pins as mounting devices even on octal sockets but like the above photo shows I did do it in several Zwreck style builds.

Mark

[sluckey]

Here's a pic that shows pin 1 internally connected to pin 2 in a RCA 6BQ5 (same as EL84). This issue comes up occasionally on Hoffman's forum because Doug mounts grid stoppers between pin 1 and pin 2 on his AC30 layout. So, if this tube were plugged into an amp wired like that, then the grid stopper would be shorted out. Not a big deal. But what if someone mounted a screen resistor between pin 1 and pin 9? Using this tube would be a BIG DEAL!

[BLT]

I agree Mark, my picture was on a Spitfire type build that I decided to try the tie points. It works fine with the JJ EL84's I have in it, but I may change it to more of a Rocket look. I do like the idea of the resistor being less susceptible to vibration by tying it to 2 points.

[M Fowler]

When I can I either use turret strips or individual insulated stud turret bolted to chassis.

Some examples of EL84 tubed amps I've built

[tubeswell]

RCA and GE datasheets don't indicate whether Pins 1, 6 and 8 are 'NC' or 'IC'. If in doubt inspect the pins connections inside the base of the bottle at the pin-end of the electrode cage (as per Steve's pic)