# Phase Inverter: 6SN7 vs. 6SL7



## Tyler Savage (Nov 16, 2009)

I've got two old tube Garnet PA amp heads. They're actually quite great sounding for guitar.

The Rebel has one has 12ax7s on each channel + second 12ax7 stage + 6SL7 phase inverter + 6L6 output
The Pro has 12ax7 on each channel + + second 12ax7 stage + 6SN7 phase inverter + EL34 output

Somewhat similar sounding, but definitely different animals. 
Right now the Rebel can get some gnarly grind out of it when it's cranked. The Pro.. not so much (and it's far noisier)

The pro definitely doesn't have as much gain going on. Investigating it, I found that the 6SN7 has a much lower amplification factor that the 6SL7 (20 vs. 70 respectively). 6SL7s are often used in hifi, and are quite linear sounding, etc. etc. Considering this was a PA head, I'm guessing this was a good thing to do.

But I want to use it for guitar! Various places online say you can't just sub in a 6SL7 for a 6SN7.. that the transconductance, current load, and other things don't match up. But no-one suggests how you might go about compensating for these discrepancies.

I'd like to give this amp more gain, and the phase inverter tube is an easy place to start. I'd rather use a 6SN7 instead of a 12ax7 because so far, I really like the tone that the other garnet has, and I have enough amps with complete 12ax7 input sections. 

after this I plan on cascading the inputs, and see what happens!


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## bolero (Oct 11, 2006)

I have a rebel & it is truly a kickass little amp...but don't tell too many people! lol


I'll check to see which PI tube it's got


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## Tyler Savage (Nov 16, 2009)

cool, thanks! and I know - too many people already flipping traynor bassmasters etc. on craigslist as is .. I don't want the same thing to happen with garnets. 

I guess what I'm looking to find out is what I can do to run a 6SL7 safely in my amp that's designed for a 6SN7 ..


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## Wild Bill (May 3, 2006)

Tyler Savage said:


> cool, thanks! and I know - too many people already flipping traynor bassmasters etc. on craigslist as is .. I don't want the same thing to happen with garnets.
> 
> I guess what I'm looking to find out is what I can do to run a 6SL7 safely in my amp that's designed for a 6SN7 ..


Hi Tyler!

The 6SN7 is very similar to a 12AU7, as is the 6SL7 to a 12AX7. In a longtailed PI, I would use the appropriate resistors for the smaller tubes. That should be "close enough for rock and roll"!

That means for a 6SL7 use the typical Marshall resistor values - 82k/100k for the plates, 470 ohm down through 10k on the joined cathodes.

There's a very good FAQ on PI's (actually, TWO of them!) here:

Aiken Amplification

Have fun!

WB


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## Tyler Savage (Nov 16, 2009)

Thanks Bill!

I still need to bring my Marshall down to you. I keep thinking I have to goto stoney creek for work then it doesn't happen


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