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QRX-9001, one last problem...

Wickeviking

Wickeviking

Goran
Hello! I have a very carefully renewed and calibrated QRX-9001. It is sounding and performing perfectly. But I still have one problem to deal with. Sense I changed all of the caps in the radio section, I now have this problem with temperature related drift. AK member Lefty once wrote this about this problem.

-“Most of the better quality vintage analog tuners I have run across relied on thermal compensation in the FM front end section to deal with drift. This is where hand selected capacitors are installed into the local oscillator circuit at final testing stage of manufacture. The service manual will sometimes show which of these certain capacitors may have slightly different values both in capacitance and or in temperature response. These capacitors can be selected to either increase or decrease in value with raising temperature. The bad news is if one is seeing drift in a tuner of this kind it is very difficult to correct for the average hobbyist. It requires a very accurate frequency counter to measure the drift and then cut and try different compensation capacitors to correct it. The good news is that I have personally never come across a noticeable drifting tuner or receiver in my 5 years of collecting this stuff. I have been amazed at how well that these better analog tuners and receivers perform in this area. I will tune in a station at first turn on and look again an hour later and detect no movement in the tuning meter. This is no easy task to design and build in and is a real indication of the talent and skill that was used in building this equipment.”

So, I have changed those caps and tried different combinations with varying results, but never a good one. Have any of you found the magic combination??? And if so, what caps did you use?

/Goran
 
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Wickeviking said:
Hello! I have a very carefully renewed and calibrated QRX-9001. It is sounding and performing perfectly. But I still have one problem to deal with. Sense I changed all of the caps in the radio section, I now have this problem with temperature related drift. AK member Lefty once wrote this about this problem.

-“Most of the better quality vintage analog tuners I have run across relied on thermal compensation in the FM front end section to deal with drift. This is where hand selected capacitors are installed into the local oscillator circuit at final testing stage of manufacture. The service manual will sometimes show which of these certain capacitors may have slightly different values both in capacitance and or in temperature response. These capacitors can be selected to either increase or decrease in value with raising temperature. The bad news is if one is seeing drift in a tuner of this kind it is very difficult to correct for the average hobbyist. It requires a very accurate frequency counter to measure the drift and then cut and try different compensation capacitors to correct it. The good news is that I have personally never come across a noticeable drifting tuner or receiver in my 5 years of collecting this stuff. I have been amazed at how well that these better analog tuners and receivers perform in this area. I will tune in a station at first turn on and look again an hour later and detect no movement in the tuning meter. This is no easy task to design and build in and is a real indication of the talent and skill that was used in building this equipment.”

So, I have changed those caps and tried different combinations with varying results, but never a good one. Have any of you found the magic combination??? And if so, what caps did you use?

/Goran
Click to expand...

Wow, Goran, I don't know what to tell you about this but in my opinion one should never dabble in an RF section. This is due to the extreme care and test equipment used at the factory to select those components and then align them to spec. I am not a big fan of replacing any capacitive components except for old electrolytics -- all other capacitive devicies seldom change value.

You need to locate a tech with experience in RF alignment and who has the necessary gear to do this alignment.

Paul
 
Just for clarification, I only changed the electrolytic caps. And that is the caps concerned here. And I have tried to find someone in Stockholm who can help me with this, but it is obviosely a dying art...I'm capable of trimming the radio section to perfect perfomance, but this temperature related problem seems to be more than I can handle.
/Goran
 
Shoot your question over to Quad Bob at Quadraphonic Quad forums he has been doing complete restorations of 9001's for several years.He is our guru for the Sansui QRX series.
 
Wickeviking said:
Just for clarification, I only changed the electrolytic caps. And that is the caps concerned here. And I have tried to find someone in Stockholm who can help me with this, but it is obviosely a dying art...I'm capable of trimming the radio section to perfect perfomance, but this temperature related problem seems to be more than I can handle.
/Goran
Click to expand...

Your right -- that is odd if all you replaced was the old electrolytics. I too can set-up a tuner but I don't like to :no: even with reasonably good test equipment -- RF alignment is both art and science. :thumbsdn:

If it's drifting with time (and, I'm guessing, it's heat related) have you tried freeze-spray on the oscillators, mixers and IF circuits to determine which component is causing the frequency to drift. These are certainly very difficult to work on. Do you have a generator or must you use off-the-air signals?

Paul
 
Tank’s for the replies. I have found out which caps are involved. But can't find out what caps to use that have the compensating characteristics. It will be too much digging thru data sheets witch I don’t have. Where can I find data cheets for the old Nichicon capacitors that were in there from the beginning?
And I have tried Quadraphonic Quad forums and no reply so far. And I’m using off the air signals from some good local radio stations that only transmit carrier waves at night time.
/Goran
 
Wickeviking said:
Tank’s for the replies. I have found out which caps are involved. But can't find out what caps to use that have the compensating characteristics. It will be too much digging thru data sheets witch I don’t have. Where can I find data cheets for the old Nichicon capacitors that were in there from the beginning?
And I have tried Quadraphonic Quad forums and no reply so far. And I’m using off the air signals from some good local radio stations that only transmit carrier waves at night time.
/Goran
Click to expand...

Have you tried contacting someone over at the TIC? With their expertise in tiuners someone there might have the info you need.

Paul
 
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