Hallicrafters SX-101a Reception Issues

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ashleyct3

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#1
I have an SX-101A which appears to work fine. The issue is that when I tune around on SSB, the inauduble part of the signal is booming. Then when tuned to where it is audible, the signal is so low I can almost not hear it. Is this normal for this radio? I have not experienced this issue with any other radio in the past.
 
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#2
The inaudible part? You mean the silence between words? If you have the AVC turned on, the receiver has no carrier to operate the AGC so it turns the gain right up full. The method to stop this is easy - turn the AGC off then turn down the RF gain until you can barely hear the background noise. Then tune in your SSB signal and increase the RF gain to make it sound loud enough but not enough to bring the noise up loud.
 

ashleyct3

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#3
Let me clarify a little. The "inaudible" sound is the worble sound of SSB. Or maybe I should have said Unintelligible. When I tune until it is Intelligible, The audio is very low...
 
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#4
If I had to take a couple stabs at this, either your product detector tubes (6BJ7? and 6BY6) need a couple re-seats into the socket and/or a cleaning of the socket holes and tube pins; or you aren't using a narrower bandwidth like at least 5 or 2.5kHz. because if you're using say 10kHz wide stronger signals will still be warbled in SSB. Start there.
EDIT: from what I skimmed on this I think you have two product detector tubes-funny, I only have the 6AL5 for that in my SX-88.
 
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ashleyct3

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#5
I think the Detector Tube is a 6BY6 as well as the Mixer. I'll re-seat both of them and make sure that the pins are clean, and let you know what happens. Thanks
 
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#6
It will take a combination of the main tuning dial and pitch control together to get the SSB voice sounding right. The receiver has to have the BFO enabled (I forget how). You then run the volume up kind of high and use the RF gain for a comfortable level of audio and quiet background.

I had an SX-101A in high school and should have never sold it.
prcguy
 
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#7
I understand now. The problem is that you have two controls that affect the sound - the BFO and the main tuning. The BFO is there to replace the suppressed carrier but you should not be able to hear it. To set the BFO to the correct frequency, tune in an AM BC station as exact as you can, turn the BFO on and tune the BFO pitch control for zero beat - leave the BFO alone from now on (but check it occasionally as it may drift). Now go back to your SSB station and carefully tune through it, it may be Lower or Upper sideband. At one point the transmission should come perfectly clear - reduce the RF gain and increase the AF to finally clean up the signal. Amateurs are not good at being all on the same frequency unfortunately so you may have to carefully tweak the main tuning at every 'over'.
 
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#8
I had an SX-101A in high school and should have never sold it.
prcguy
YES !

There was one at the college ham club station... mid-60s state of the art... what a great radio.
The thing weighed a ton (actually 75 lbs.).

The 6BY6 is the product detector in the "A" model.

You got some good advice on how to tune in a SSB signal, playing with the BFO is pretty much a thing of the past but with a little practice you should be able to get it right.

Have fun and enjoy your SX-101A. :)
 
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