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In Reply to: RE: Ferite beads instead of CC grid stopper resistors ? posted by Dyna Saur on May 22, 2007 at 05:13:40
I have not researched this in detail, but it's my understanding that there are two kinds of ferrite sleeves. Some become resistive at high frequencies, some remain inductive. For grid stopper applications, you want the resistive kind.Don't ask me for part numbers - I have not researched it. If you do, we would all benefit from sharing your experience! :^)
Just a note - as the late John "Buddha" Camille wrote several times, VHF oscillation problems are often very transient and hence hard to identify. A 400MHz or better 'scope is the minimum tool, but more important is a good sense of what to test and how to test it. (Now that Buddha is gone, I can't say that I actually know anyone with that kind and amount of expertise.) Often only certain conditions of voltage and slew rate will trigger these transient blips.
He found this to be particularly true of 6DJ8s, and introduced me to the idea of using plate stoppers as well as grid stoppers (as we do in Seduction). He felt the subjective effect [of these transient oscillations] was often a subtle glassy sheen, sometimes mistaken for increased resolution but ultimately tiring to listen to. I have not found that with Seduction, and the wide acceptance of this otherwise fairly simple circuit suggests that others are also happy.
[edited to clarify]
Edits: 05/22/07Follow Ups:
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