[Hallicrafters] SX-101 Problems

[Bill Gerhold]

No such thing as a "weak" transformer.  It is either good or bad, sometimes
very bad.  The fact you have low voltage in all stages, I would check to be
sure you actually have 117vac on the primary of the transformer.  Check the
fuse for some modification or other changes in the 117vac primary circuit.
If this checks out OK, I would then check the secondary windings of the
transformer for proper AC voltages.  I am attaching a guide to identify the
windings on the transformer.  If the colors on the wires are still visible,
you can use this.  

Power Transformers winding identifiers:

Primary Leads Black (if tapped) Common Black 
Tap Black / Yellow
End Black / Red 

High Voltage Winding Red (center tap) Red / Yellow 
Rectifier Filament Winding Yellow (center tap) Yellow / Blue 
Filament Winding #1 Green (center tap) Green / Yellow 
Filament Winding #2 Brown (center tap) Brown / Yellow 
Filament Winding #3 Slate (center tap) Slate / Yellow

Another thing you may want to consider, the bands at this time are LOUSY.
Just this morning I tuned across 20 and found absolutely nothing and this
was on and ICOM 756pro.

Good luck, but from your description, it sounds like a problem that is
common to the entire radio which could make the problem a simple fix.
Hopefully, the transformer is good.

K2WH


-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of robert Keeble
Sent: Saturday, July 16, 2005 12:57 PM
To: Hallicrafters at mailman.qth.net
Subject: [Hallicrafters] SX-101 Problems

Need advice from the group!
SX-101 Mark I. Was not receiving when I got it but could hear very faint 
signals through atmospheric noise.
Replaced all Black beauties and Red Chiefs and can lytic.

    * Radio powers up with atmospheric noise but no signals on any band. 

    * Signal from generator applied to antenna input shows up at antenna
      coils and changes with band switch and signal generator frequency
      to show up at proper ant. coil.

    * Signal also shows up at mixer coils at higher level.

    * Signal does not show up at Osc coils.

    * No signal heard at all when tuning across the dial on any band.

    * With outside antenna (only at night)... multiple broadcast
      stations heard at the same time but tuning up and down the band
      has no effect. Activity is louder on 160 and weaker as I go up to
      80 , 40 etc.

    * When measuring tube voltages I am getting only 2 VAC on all  tube
      heaters when it calls for 6.3 VAC.  Also removed the 5Y3 Rectifier
      and and measured across the heater secondary and read only 2 VAC
      directly from transformer. (Secondary 6.3 leads show evidence of
      overheating, right near the 5Y3 socket)

    * All plate voltages check low, some lower than others. Worst are
      1st RF amp *160, should be 210,* 1st mixer *180, should be 240*, 
      1st IF amp *175, should be 210* *  *1st conv oscillator/cathode
      follower  *130, should be 150*  and at rectifier* 220,  should be
      280.*
    * *Grid voltage on 1st conv/osc shows zero on pin 2 and 7 and should
      be -12 and -4 respectively.*
    * *Dial lamps appear to be dim  to me (dull orange)
      *

Could the transformer be weak enough that the later stages are affected 
more than the earlier ones?
Have substituted known good tubes for most all of the existing except 
for the 6BJ7 Det/ANL/AVC. (don't have  a spare)
Any thoughts will be appreciated,  Bob,  KG4NVX

KG4NVX at igiles.net
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