2. amps-preamps
  3. 119397-46

Balanced Audio Technology Preamp - Tube compatibility question - Help

Hello,

I have a BAT VK-3ix preamp and I just purchased some 1950's Sylvania 6v6GT tubes for it (presumably a power tubes of some sort).  I was going to install it and I noticed it had an extra pin in the number 1 pin location.  Pin number one I think.  According to Audiotubes.com the number 1 pin of gray glass tubes:


 NOTE ON THE METAL SHELL 6V6 TYPE: Pin 1 of the 6V6 family of tubes is usually not connected in the glass tubes, although some of the greyglass types may have the pin internally connected to the grey RF shield. The metal jacket 6V6 (no suffix) has PIN 1 CONNECTED TO THE METAL SHELL. This effectively turns pin 1 into a GROUND PIN. It is important to make sure there is no voltage or active circuit connection (other than ground) on the pin 1 connection for the 6V6 tube in your amp if you plan to use a metal shell 6V6 tube. IMPORTANT NOTE: You should ALWAYS check and/or adjust your amp output tube's bias settings when replacing 6V6 or ANY power output tube!


I bought my tubes from the Tubedepot.com and I even asked if they would work in my unit.  They said they would, but now I'm getting cold feet and don't want to blow up my gear! The ceramic input does have a connection in the pin so Im note sure.


I

last_lemming
4 responses Add your response
noromance's avatar
noromance
9,384 posts
 
Stand on a rubber mat, one hand behind your back and the other on the power switch just in case it flares up. Ok, I'm kidding, mostly.
atmasphere's avatar
atmasphere
11,556 posts
 
I would not worry about this at all. If pin one is connected to something, so what? You don't have a metal base tube, but if you did pin one would be the case of the tube- even then it would not amount to anything. So play it with no worries.
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
As I read it the cautions in the statement you quoted only apply to the metal versions of the 6V6, and you have glass tubes. So while per the statement it is possible that pin 1 is connected to the grey shielding (which would seem very unlikely to result in any issues), I see nothing to indicate a possibility that it could be connected to anything else in the tube.

Also, FWIW, an older GE tube manual I have has a single pin diagram for all of the 6V6 variants, which shows no connection between pin 1 and any other internal element or any other pin. With pin 1 being designated as "S/NC," which I presume means that it may either be internally connected to the "Shell," or there is "No Connection" internally.

If you have a multimeter handy it can’t hurt to see if there is any measurable resistance between pin 1 and each of the other pins, but even if you don’t do that I don’t see any indication of a risk in the quoted statement or in the tube manual.

If you do make those multimeter measurements, btw, be sure to keep your fingers off of the metal tips of the test leads (or at least one of them), or you may get a false positive as a result of measuring the resistance of your body.

Regards,
-- Al

last_lemming OP
626 posts
 
So I've basically gotten nowhere with this question. I've even spoken to Victor at BAT and he briefly looked at the schematics but did have time for an in depth review to tell me if there is a signal going to pin 1 in the ceramic base. Even if he could he said it would also depend on what pin 1 in the tube was connected to, and he wasn't sure of that either. 

I can't tell by looking at the tube where the internal wire that comes off pin 1 goes because the internal surface is coated with a gray RF spray.  The glass is clear for only about 1/8 inch before the tube goes gray so I can only see that it goes straight up but that is all. 
 
There is as far as I can tell 2 possibilities:

1.  Pin 1 is connected to the gray sprayed on shielding.
2. Pin 1 is connected to some othe internal components of the tube that will see voltage. 

How owe these two possibilities will interact with the preamp is unknown to me of course. 

Is there a way to test the pins with a multimeter to shed any more light on the subject?
Log in to respond
More to discover
80x80
Jeff Rowland CORUS
80x80
McCormack MAP-1
80x80
EAR (Esoteric Audio Research) 890