[NJARC] Hallicrafters SX-16 PS

[Jim Whartenby]

Scott
When a tube looses vacuum, something has to leak in.  The purple glow
is from excited gas ions.  I wouldn't even bother to test the
rectifier, just replace it.

There are special classes of vacuum tubes, voltage regulators and
mercury vapor rectifiers that work with intentionally added gas vapors.
 They will have a colored glow.

As to the the high voltage secondary.  The measured resistance should
be a couple of hundred ohms.  Make sure you make good contact with the
tube socket and ground.

A note of caution.  Since the winding has many turns and the
transformer is most likely not bifilar wound, that is both sections of
the secondary are not wound together, the inner layers are shorter in
length then the outer windings.  What is important is the number of
turns, not the length of the wire.  So the outer HV secondary will have
a longer length of wire then the inner winding and therefore will have
higher resistance.

Check the transformer as the last e-mail suggests.  Pull the tubes and
let it run.  You can check the high voltage secondary to ground at this
time.  Note that the voltages are very close but the wire resistance is
not.
Jim

--- Scott Roberts <ng19delta at yahoo.com> wrote:

> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Thanks Jim-
> Would a rectifier just "go gassy"? When I was testing the radio
> the night before, the tube had a purple glow to it on both sides.
> I was not sure if this was normal, and had been planning to ask,
> but last night the purple glow had the addition of lightning,
> which was quite disconcerting... Or deconcerting, had I had a
> concert on the radio... (Ow!)
> 
> I will check the voltages to ground: and am still checking
> continuity through the turns  of the transformer, but it appears
> the 110 primary has continuity(once the power switch is on), the
> heater secondary has continuity, and need to review both sides of
> the turns for the 5Z3 tube.
> 
> Scott
> 
> --- Jim Whartenby <antqradio at sbcglobal.net> wrote:
> 
> > Visit our web site - See http://www.njarc.org
> > _______________________________________________
> > Scott
> > I wouldn't go through all of the trouble of disconnecting the
> > transformer secondaries at this time.  The problem could be
> > just a
> > gassy rectifier.
> > 
> > If you pull all of the tubes and apply power, the transformer
> > will be
> > unloaded.  Let the set run for a half hour or more with the
> > transformer
> > unloaded while checking the transformer's temperature.
> > 
> > If it is just barely warm to the touch then the transformer is
> > most
> > likely OK.  If the filament winding reads between 6 and 7 VAC
> > then you
> > know the transformer is working properly.  Expect higher then
> > normal
> > voltages since the copper losses are nil.  You are not pulling
> > any
> > power out of the transformer when it is unloaded.  The only
> > power used
> > is that which is required to set up the magnetic field and
> > supply the
> > back EMF to the primary.
> > 
> > If you hear a slight buzz or notice that "burnt smell" AND the
> > transformer gets noticeably warmer then the rest of the
> > chassis, then
> > there may be reason for concern.  A shorted turn will pull
> > power from
> > the primary which will directly heat up the transformer.
> > 
> > Some transformer problems are from leakage to ground instead of
> > a
> > shorted turn.  You can check each side of the high voltage
> > secondary to
> > ground for the same voltage.  The voltage readings should be
> > very
> > close.  The low voltage windings are a bit harder to test for
> > leakage
> > since it is common practice in some sets to try to reduce the
> > filament
> > induced hum.  It might be necessary to disconnect the low
> > voltage
> > windings in order to check for leakage there.
> > 
> > Lastly, poorly designed and mounted transformers may actually
> > induce
> > current into the chassis which in effect becomes a shorted
> > turn.  The
> > cure is to space the transformer a bit above the chassis to
> > reduce this
> > coupling.  So if the transformer gets warm but is otherwise OK,
> > spacing
> > could be the issue.
> > Regards,
> > Jim
> 
> 
> 
>      
>
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