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In Reply to: How important is the quality of a triode used as a cathode follower? posted by Ray Moth on April 6, 2007 at 02:37:26:
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I have some Sovtek 6SN7s, which are not generally considered to be among the best sounding tubes of that type. However, I wondered if they would sound any worse than other 6SN7s as cathode followers?
"...Sovtek 6SN7s, which are not generally considered to be among the best sounding tubes of that type."I must agree with you there. I have tried them as a White Follower and found them to be fairly good. BTW I couldn't stand them in any other application I've tried. Check out
http://journals.aol.com/php289/TubeTown/
and you'll see what I mean.Have fun.
Pete.
...so can't answer the question from experience.But, in all my preamps for the past 25 years I've used either 6922 or 6H30's as SLCF cathode followers - and the quality of the actual triode that is the cathode follower in that package of triodes is by far the most sonically important - far more so than the actual gain tubes preceeding them!
Yes, I see, indeed the 6SN7 has a gm of only about 2600 umho (on a good day).Allen, in your opinion, would a MOSFET source follower, with its high gm, be as good as or better than a tube cathode follower for driving an OP tube? I want to try a direct-coupled cf or sf driver, to avoid blocking distortion and, possibly, to get a little more headroom for transients by letting the OP tube go into AB2 (but not to operate in AB2 continuously).
..., with its high gm, be as good as or better than a tube..."In my experience - no fet, either junction or MOS, should be allowed anywhere the primary signal path in any amp!
The only exception is the use of a very low noise jfet as the lower half of an cascode in the input of a RIAA stage. There the greatly reduced (and consistantly low) noise compared to any tube is a huge benefit - and it seems that the sonic contribution of the jfet is effectively inaudible.
But a MOSFET source follower - nein danke!
If you really need a CF driver - the ONLY thing that I would use is my SLCF - that is transparent and with enough current through (say) 6H30's will drive most anything you want - including 30 ohm headphones!
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