[Hallicrafters] Help with SX-99 xfmr replacement

[Mike Everette]

Do you know if your "donor" SX-99 was actually marked
as SX-99U?  In that case the transformer that came
from it would be a dual 110-220 volt primary.  I have
never seen an SX-99U but have seen an S-40U and the
transformer in that radio had a knob-like selector on
top of its case for switching between 110 and 220.  I
have a dual-primary transformer for an SX-28 that has
a slide switch on top for selecting the voltage.  In
the case of both these transformers, there would only
be two primary leads emerging from the transformer
itself.

The color codes you are hearing about may not be
standard; nor may the ones on your transformer.  The
standard transformer color code is black for primary,
but I have also seen black on one lead and slate-gray
on the other.  The high voltage secondary should be
red-red, with a red-with-yellow-stripe center tap. 
The 6 volt filament winding should be green; if it had
a center tap -- and the SX-99 transformer does not, if
I recall -- that would be green-green with a yellow
stripe, or green-yellow.  The 5 volt filament winding
should be yellow-yellow, and if it had a center tap --
again, the SX-99 transformer's 5 volt winding does not
-- it would be yellow with a red stripe, if memory
serves.  

BEWARE, the Halli transformers may not have used the
standard code!

The HV secondary leads go to the plates of the
rectifier tube.  The center tap goes to ground.

The 5 volt winding goes to the rectifier filaments.

One end of the 6 volt winding goes to ground.  The
other end feeds the filaments and dial lights.

One side of the primary goes to the AC line.  The
other side is fed from the on-off switch.

If you don't have a Sams Photofact on this receiver,
you should get one.  If you should happen to have one
for the SX-110 but not the 99, you can use the 110
Photofact.  Under the chassis the radios are
identical, except for the mechanical details of the
dial drive.  Yes, the parts layout is the same, or 99%
so at least.  The circuitry is identical.

Some people may diss me over this next point, but if I
were you, I'd remove the capacitor bypassing the AC
line to ground and not worry about replacing it. 
There is, I believe, also a 470K ohm resistor or some
such, from one side of the AC line to ground as well. 
I'd get rid of that too.  I have been "filled with the
gl-LOW-ry of the Lord" a few times -- near'bout shook
hands with Him, once -- because of leakage through
these line bypasses, and it ain't no fun, folks.  Keep
the AC OFF the chassis.

73

Mike
WA4DLF




 
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