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In Reply to: How do I lower the gain of a 6SN7-based SET? Is there a family tube with lower gain... posted by jeffreybehr on March 11, 2007 at 20:23:11:
...are pinout-compatible with 6SN7, but gain is only moderately lower, and the plate resistance is considerably lower in both; so circuit modifications might be needed. You can look them up on duncanamps.com.
Follow Ups:
...that you also have to pay attention to the filament draw. In the 6BL7 it is also much higher than the 6SN7, so you would have to be sure your power transformer could handle it.If you are going to consider transformers, I suppose you could replace the coupling capacitor to the output with an IT (in each channel) connected as a step-down. The voltage ratio equals the turns ratio, while the impedance goes like the square of the voltage, so this would be beneficial from the current drive standpoint as well.
Be very wary with the 6BX7 since the filament takes double the current of a 6SN7. It will aslo give a cleaner bass due to the low Rp.
I would suggest an alternative solution in that you can fit a Lundhall input trannie: this can be configured to give 1:1 or 2:1 or even 4:1 without sacrificing the cleanliness or the dynamic range of the incoming signal. This resolves the problem of excessive gain when using horns.
I use the nickel core type for this purpose.
Hope this helps.
John R
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
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