Wickeviking
New member
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 electrolytic 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 electrolytic 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
-“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 electrolytic 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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