• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Sovtek 6BQ5\EL84 different internal connections!

markn2wae

markn2wae

Mark T N2WAE
I stumbled onto this situation while testing 6BQ5\EL84 tubes with my TV-7U tube tester and found a strange anomaly between the Sovtek tubes and other "domestic" and other old stock I had kicking around in my junk box.

It seems that while testing the "non Sovtek" tubes, you will get a short indication on short test switch positions 1,2,3 and 5 (grid switch set to #2 as per setup) even on a good working tube.

Putting the grid switch on #1 cleared the abnormal short indications and still let you test the tube properly (no change in meter reading between grid positions 1 or 2)

Enter the Sovetek 6BQ5, now with the grid switch set to #2 (per setup) the tube still tests good but no more "short indications!":scratch2:

Put the grid selector in the #1 position and the test reading goes down to half the reading it was (above showed NO change).

I investigated the problem and found that the Sovtek tube has NO CONNECTION to pin #1 (the "US" tubes had pins 1 and 2 connected internally)
It functioned as a mica support point and connected to nothing.

The 2 other IC (internal connection) pins 6 and 8 are the same for all tubes, and go "no place".

The above just points out that the tubes test differently, and should not effect how they perform in the circuit (keep in mind, NEVER use a IC pin on a tube for a tie point for other components!)

Thought I'd pass this along.

Mark T.:music:
 

Attachments

  • 6BQ5_EL84.jpg
    6BQ5_EL84.jpg
    39.9 KB · Views: 54
Register to hide this ad
I've noticed this myself - some Telefunkens are different too. 1, 6 and 8 are "internal connection" or nothing at all. 7189A uses these pins as duplicate connections for grid and screen.
 
This is great information guys. I've never used a "unused" socket terminal for a tie point, but boy someone did on the old Heathkit I'm presently working on. This is just the kind of stuff that could get a guy like me (solder slinger with very limited knowledge) in big trouble. Thanks for the heads up, Jay
 
I have seen on 5U4/5Y3 sockets the unused pins right next to the plates used as tie points for 110 volt AC input...I usually try to re-wire these circuits so the 110 AC connection is not made here.

Also there can be a problem where pin #1 on an octal socket is used as a tie point where a glass tube was originally used and when a metal tube is inserted the shell connects to that pin...if there is HV on that pin 1 this will be a shock hazard. Later (70's/80's) GE metal tubes printed a warning about this on the tube itself that the shell connects to pin 1.
 
Just corroborated this point with Sovtek EL84/6BQ5 tubes on my Precision Tube Master Series 10-12. The data sheet calls for a grid short to be present when depressing element short buttons 1+2.

Probably irrelevant posting, after all these years, but there you have it for posterity.
 
markn2wae said:
I stumbled onto this situation while testing 6BQ5\EL84 tubes with my TV-7U tube tester and found a strange anomaly between the Sovtek tubes and other "domestic" and other old stock I had kicking around in my junk box.

It seems that while testing the "non Sovtek" tubes, you will get a short indication on short test switch positions 1,2,3 and 5 (grid switch set to #2 as per setup) even on a good working tube.

Putting the grid switch on #1 cleared the abnormal short indications and still let you test the tube properly (no change in meter reading between grid positions 1 or 2)

Enter the Sovetek 6BQ5, now with the grid switch set to #2 (per setup) the tube still tests good but no more "short indications!":scratch2:

Put the grid selector in the #1 position and the test reading goes down to half the reading it was (above showed NO change).

I investigated the problem and found that the Sovtek tube has NO CONNECTION to pin #1 (the "US" tubes had pins 1 and 2 connected internally)
It functioned as a mica support point and connected to nothing.

The 2 other IC (internal connection) pins 6 and 8 are the same for all tubes, and go "no place".

The above just points out that the tubes test differently, and should not effect how they perform in the circuit (keep in mind, NEVER use a IC pin on a tube for a tie point for other components!)

Thought I'd pass this along.

Mark T.:music:
Click to expand...

Those internal connections to the grids of military 6N14P-EV and the US made 7189A are for heat dissipation function. So, don't tied anything to what you may think are "open" pins on the -EV or 7189A. The US made 7189 has the same pinout (and open pins) as the standard EL84.

EL84 pinout.jpg

7189A pinout.jpg
 
You must log in or register to reply here.
Back
Top Bottom