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6SN7 - what should I use it for? :-D

1/13/2005 6:22 PM
6SN7 - what should I use it for? :-D
I just acquired a bunch of old tubes to play with. mostly octal preamp pentodes, which I love dearly, but also a 6SN7. It seems to be a pretty low-gain, high-current tube so i thought maybe it would go nicely as a phase inverter.  
Has anyone got any favourite uses for the 6SN7? the one i have is an old RCA glass tube one. some googling told me the Model 26 Fender Deluxe and the 5A3 Fender Deluxe both used them as preamp tubes as well which is interesting!  
the amp i want to use it in is a 6SJ7 -> 12AX7 -> 2x 6V6GT amp. it would be pretty cool to get rid of that one last noval tube ;-)  
any advice appreciated!  
New Zealand
1/13/2005 6:58 PM
Wild Bill

Darren, the tube is a lot like an 8-pin version of a 12AU7. Look for these circuits and you'll have an easy conversion.  
You could replace that 12AX7 and use lower value plate resistors. I'm not sure of the exact value. Check the tube data sheets for the 6SN7, find the plate load and double it for a good start. Probably 12AU7 values would be ok.  
The gain is much less, like 10 or so for voltage but with that 6SJ7 driving it you should still have enough for full output from the 6V6's. The amp will sound much cleaner without nearly as much preamp breakup, if any. The Duncan Amps site has some schematics of old hifi amps that use the 6SN7 as a PI.  
Or you could find a 6SL7, which has the same pinout but a voltage gain almost as high as a 12AX7. I've used 'em many times before. They have a tendency to be microphonic when used as the 1st tube in the string but I've never had a problem when using them for a PI. I use the same plate resistors as the 12AX7 but you can check out old Ampeg schematics or go to Aiken Amps site. Randall Aiken has two great tech FAQ on long-tailed pairs. I think it's the second in the list which actually uses the 6SL7 as the example, with part values.  
---Wild Bill
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1/13/2005 7:06 PM

Cheers Bill. I would actually love to get significantly less gain out of this amp!  
I love that LTP article, I use it on every amp. Hope fully I'll like this tube as a PI :-) This amp is already my favourite ever *grin*  
Thanks for your writing!  
New Zealand
1/13/2005 7:00 PM
what should you use it for?  
a butt plug.
1/13/2005 7:07 PM

k! I even painted your face on it!  
1/13/2005 7:33 PM
i was just making a joke. you obviously caught on.  
but a good way to use a 6sn7 is to wire an actal socket in parallel with a 12ax7 socket of your choice in one of your existing homemade amps and then substitute the 6sn7 for the 12ax7. the 6sn7 will sound a bit fatter with less highs. see the angela instruments super champ amp for more about this.  
the parallel socket idea also lets you run both the 6sn7 and 12ax7 in parallel which results in a slightly more gain considering the internal plate resistance is approximately cut in half using two tubes.
1/13/2005 7:43 PM

Oh! you'd want to use a 6SL7 probably, that's an octal 6V equivalent of a 12AX7. :-)  
I used to have a matchless spitfire clone that used parallelled triodes - it sounded pretty cool actually. bigger in some undefineable way, and yeah extra gain due to the oversized plate load. the big bottles do always seem to sound 'fatter' as well aye, i wonder how much of that is psychosomatic?  
weekend of tinkering ahead, methinks :-D
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