On Wed, 30 Sep 1998 11:38:49 -0700 (PDT) david wintheiser
<w0opw@yahoo.com> writes:
> Carl, please elucidate on your commnet about Svetlana 572b's. Not
>that I have any, just curious why you downgrade the tubes - Pat W0OPW
The reason is that I have had continual problems with them in certain
amps. I believe that the difference in capacitance due to the ceramic
base plus the higher gain can make a marginally stable amp go parasitic.
They are also not rated at 6M but that is a different issue and I suspect
that Svetlana was aware of the instability when they wrote the spec
sheet.
A redesigned parasitic suppressor works well.
In the case of the Yaesu FL-2100 the factory AND Svetlana mods are
marginal in providing sufficient cut-off voltage. I had to add parts to
develop -125VDC cut-off as in the SB-200 in order to support all tubes.
The above mods are doable by a technically competent person but that
leaves out the majority of hams today.
My last pair of Svetlana's are doing modulator duty in my Clegg Zeus.
73 Carl KM1H
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