6386 to 6BA6 T-bar

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schrobbelbop

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Can someone help me out with a schematic or a "how to" wire 2  6BA6 to a 6386 socket?

i want to make T-bar mod's for my Sta-level, the JJ 6386 seem very hard to get thump free. I've had 4 diffrent ones and 1
was okay. so planning to adapt to 6ba6, maybe also for my drip 670 when those tubes need replacement.

thnx
 

emrr

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I think I'm remembering someone here making some boards for that very purpose.  Been awhile......
 

CJ

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i think we have been around this block several times, look in the "Poor Mans 670 " thread, might be some stuff there.

 

mjrippe

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Here is a sort of "how to":

First look up the pinouts for both tubes and write them down or print them out. 
The filaments of the 6BA6 get tied together in parallel. 
Then you wire the 6BA6 in triode mode, so strap pin 2 to pin 7 and pin 5 to pin 6.
Each 6BA6 now replaces one side of the 6386 so line up the pins for cathodes, grids, and anodes and you are done.
 

dmp

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The STA LEVEL build by Bernbrue includes the option of 6386 or 6BA6
The schematic shows the connections:
http://www.xaudia.com/BB/STA_LEVEL_SCHEMATIC.pdf
 

ivan

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https://web.archive.org/web/20090920023909/www.studio-techservices.com/TIDBITS/6386-Subsitution-Adapter.pdf

I found this but didn't test it
 

mjrippe

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schrobbelbop said:
thanks, that clears it up a lot. no additional resistors needed?

Ahhhh, yes, as others have indicated there is a 68 ohm resistor placed in series with pin 1 of each 6BA6.  Sorry I left that out.
 

emrr

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mjrippe said:
as others have indicated there is a 68 ohm resistor placed in series with pin 1 of each 6BA6. 

I wonder if that's really needed (doubtful) or just some more copy/paste schematic building.  Never seen historically other than large power amps, and radio transmitters.  For example it would seem to undo some of the averaging of tube properties that occurs in a Fairchild with it's multiple parallel gain reduction tubes. 
 

mjrippe

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Honestly Doug I was sort of copy/pasting that myself.  I have heard "no resistor is fine" and "you need a resistor" and this time the resistor crowd was louder in my head. I agree that in most applications you will be safe without it and I should have said so.
 

CJ

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i thought i remembere some talk a long time ago of a resistor added to tweak the BA6 more into  6386 land, but i could be wrong, i got two brain cells left, and one of them is flickering,  ???

here is a blurb from Manley>

https://www.manley.com/tech-pages/tbar

and one of their boards>





 

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