8873 filament voltage

[Ed Lambert]

Voltages are all "relative".

Relative, that is, to the voltage from which it's derived....

What input voltage are you putting into a 220 volt connection?  Possibly
240 like most of the US power mains?  That produces a calculated 6.87
volts.  Might your input be even a little higher?  It only takes 245 to
get to the reading you measured.

Sets don't work well under these conditions....  let me rephrase that:
Sets work extremely well under these conditions, they just do it for a
MUCH shorter time before failure.

If the only choice for input wiring is the "traditional" 110/220, then
you have a problem that needs attention.  You have to find a way to
reduce the input (Variac or such) or use one of the various "schemes"
such as a bucking filament transformer in series with the primary of the
tube filament transformer.  A 120 to 12.6 volt transformer run on 240
will give you 25.2 volts out.  Series the secondary of that transformer
with the primary of the tube transformer (bucking polarity) and that will
produce a nominal 220 volts from 240 (actually, more like 215) into the
transformer and much closer to 6.3 coming out.  I think I'd rather run it
a few percent low than 10 percent high.

Ed
K1ZOK



On Sat, 8 Nov 2003 21:09:11 -0500 Gregory S Poel <gspoel at CMSENERGY.COM>
writes:
> I have an SB-230 that had a badtube, the filament was open. I  just
> installed a replacement tube and I checked the filament voltage and
> it
> measured 7.05 volts. The spec sheet indicates the voltage should be
> 6.3volts. I can't help  but wonder if this is what caused the
> original
> tube to burn out. The amp is wired for 220 volt primary. Any
> thoughts on
> the proper way to reduce the filament voltage? I would sure hate to
> loose
> another tube! Thanks, Greg
>

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