610B Alignment and calibration - Printable Version
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610B Alignment and calibration - Chris Cusick - 05-10-2013
Since I had my 610B on the bench for some routine maintenance and since I now have some better test equipment (not to say a clearer idea of what I'm doing) , I decided to go back over the alignment procedure.
I managed to improve the output from the IF transformers by a fair bit but I ran into some minor issues when aligning the broadcast band.
Firstly the adjustment for the antenna compensator (adjustment number 5) has very little effect - only very very slight. Is that normal ? The oscillator trimmer and the 'padder' work as expected.
Secondly, although I'm now getting stations more accurately in the right places, I notice a tuning 'whistle' just as I tune into a station. When it's tuned in, all is well - so it's not really a big deal - but it was not there before. I'm not convinced that reception e.g. picking up weaker stations, is as good as it could be.
What did I do ?
Any thoughts or ideas greatly appreciated
Performance on SW is excellent so I have not touched that
The schematic is here :
http://www.nostalgiaair.org/Resources/798/M0013798.htm
Thanks !
Chris
RE: 610B Alignment and calibration - exray - 05-10-2013
Quote:Secondly, although I'm now getting stations more accurately in the right places, I notice a tuning 'whistle' just as I tune into a station. When it's tuned in, all is well - so it's not really a big deal - but it was not there before.
That's a symptom of oscillation in the IF amp stage. I'm assuming that the radio has been recapped? Sometimes physical placement of the caps, missing tube shields, poor grounds via rivets can cause this. A last-ditch band-aid is to detune the IF transformers slightly so that the oscillation stops.
RE: 610B Alignment and calibration - Chris Cusick - 05-10-2013
A big part of my problem was that I had the waveband switch on position 2! Very embarrassing. In position 2 , Police, you can still faintly hear the BC band over most of the dial. It sounds super now. Thanks to exray and my apologies.
Seems I always have to learn the hard way !
Chris