On Aug 3, 2004, at 8:32 AM, <pmills7@houston.rr.com> wrote:
I've been working on an SB-220 that supposedly had a bad bias
diode.....turns out
the transformer is bad. Anyone got the combo bias and filament
transformer that
they can sell?
Hello, Phil -- Most of the filament/cutoff-bias xfmr (T2) failures in a
SB-220 - or a TL-922 - are caused by a grid-filament shorted tube.
Such a tube is not easy to identify since the short typically does not
occur until the filament is hot. The filament/bias xfmr fails during
standby, when +110v is applied to the fil CT and the shorted tube
shorts out the (unfused) cutoff-bias supply. If the T2 primary had
been fused, or if the bias-supply was fused, or if R-cutoff bias had
been used instead of V-cutoff bias, or if low VHF-Q suppressors had
been used, this problem would have been unlikely to have happened.
end
thanks & 73,
Phil
W5BVB
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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