SX-101 trouble

[Kenneth G. Gordon]

Bob:

Does the SX-101 have a dual or tapped primary? Is it possible that it 
was set up for 240 VAC input and you are running it on 120 VAC?

To me, that is the most obvious possibility as long as your power 
transformer is not smelling like burnt tar, nor getting hot.

Since the voltages you are measuring appear to be about 1/2 what they 
should...

In the SX-101A, there are TWO transformers connected to the AC 
input, they could have been wired in series instead of in parallel as they 
should be.

In the MkII, there is only one transformer, and it only has a 120 VAC 
primary.

In the MkIII, they went back to two transformers, and it would certainly 
be possible for those to be wired in series.

I wonder if there isn't a wiring error.

Ken W7EKB



> t Keeble <kg4nvx at IGILES.NET> wrote:
> 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

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