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6SL7 Vs. 6SN7

8/23/2000 10:29 PM
Chris B
6SL7 Vs. 6SN7
The 6SL7's amplification factor is 70, according to the 1959 RCA tube manual that I have. The 6SN7's amp. factor is 20, so what is the differance in signal strength in the same circuit? Is it possible to use a 6SN7 as a phase inverter and get the same power output as the 6SL7? Wouldn't the sound be cleaner, or is it possible to get the same gain as the 6SL7? I have two NOS Tung-Sol 6SN7-GTBs and would like to use them in my next project. I plan to use two 6V6s push-pull and a 5Y3 rectifier with a 350V Princeton replacement transformer.  
Chris B
8/24/2000 8:53 PM

The 6SL7 will have a higher signal voltage gain across it, but requires a smaller maximum input voltage to saturate it. The 6SN7, which is the all-time linear textbook triode, has a lower signal voltage gain across it, but requires a higher input voltage for the same level of output voltage that a 6SL7 can produce. But the 6SN7 can withstand a higher input signal voltage without saturating, i.e., it has more headroom. So it depends on your circuit. How much signal do your output stage grids need for full output? How much preamp voltage is available to the phase inverter input?  
If you had a circuit, say an old Ampeg amp, that was designed with a 6SL7 PI, and without changing anything else, you replaced the PI tube with a 6SN7, the result would most likely be a cleaner amp that didn't go as loud.  
You can take a tube such as a 6SL7, with an amplification factor of 70, and by selecting the biasing & load resistors, create a circuit with an actual voltage gain of, say, only 10. Not all circuits push the voltage gain figure up near the theoretical capability of the tube. You can build a 6SN7 circuit with a voltage gain of 15.
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