[Hallicrafters] SX-101 Problems

[zuu6k at juno.com]

Hi Bob;

First of all, find your low 6.3VAC filament voltage! You must correct
this before you burn something up. You can go no farther in
troubleshooting until you fix this! If, as I suspect, you might have
measured it wrong, i.e. read wrong scale, read DC scale while measuring
AC, had the probe set for DC instead of AC, etc, it sounds like your
oscillator is not oscillating. You should not measure signal in the
oscillator stage. If it is a pentagrid converter (6BE6, 6SA7, etc) you
should have a negative voltage of several volts on grid 1 if it is
oscillating and signal on grid 3. The plate should be the IF frequency
(455 kc?). Check on this and let us know. Good luck.

Ed K6UUZ


On Sat, 16 Jul 2005 11:57:19 -0500 robert Keeble <kg4nvx at igiles.net>
writes:
> 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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