[Amps] SB-220 filament/bias transformer needed

[R.Measures]

On Aug 3, 2004, at 8:32 AM, <pmills7 at 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