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In Reply to: open wide posted by Joelt on January 3, 2005 at 18:14:37:
I've owned two tube scopes in my life. The crappier one was an old Tek 502 with a plain-jane 12AT7 cathode follower. 500kHz on a good day, drifty, noisy, and not terribly linear. The far better one was an old Tek 545 with a W differential plug-in that used... a cathode follower with a current source load and a voltage bootstrap. Solid. The first scope ended up being stripped for parts, the second sold and probably still being used today.FWIW.
Follow Ups:
notice how Joelt never answered my question of which great scope used a plain jane CF input?
Actually, the 502 used it as an intermediate stage, and used a pentode at the input. The W, a legitimately worthwhile preamp, used its follower as the input. And a VERY interesting follower it is.That said, I'm not convinced of the sonic detriments of a properly-implemented plain-jane CF.
Allen, you're not going to be convinced by me mentioning any particular scope, and you know that. One guy's anecdote that "I had a scope with a plain cathode follower in it, and it wasn't very good" is hardly proof of anything!
The undeniable fact is that even a lousy oscilloscope has to have a bandwidth and noise figure much better than even the best audio amp. And many scopes from many manufacturers used cathode follower inputs. This, to me, is proof enough that your statement that they don't belong anywhere in audio was sophomoric.
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