Alignment question - Printable Version
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Alignment question - standardtwin - 09-02-2014
On the aforementioned set, (42-380) would an alignment process "sharpen" the tuning ability of the set?. By this I mean when I get to a strong station, it seems to tune in twice, i.e. a fatter bandwidth on the dial, rather than a station that is heard only by moving the dial slightly. It picks up stations well, but I figured I'd ask the question.
For a newbie, could someone explain the process of how an alignment is performed?. I'd like to try it, but have no equipment yet. Could use a recommendation there too.
Thanks for the help!!
RE: Alignment question - PAradiogeek - 09-04-2014
Welcome,
Yes, I believe that an alignment could sharpen the tuning, assuming your radio is out of alignment in the first place.
To do an alignment you need a couple of pieces of equipment: A voltmeter to measure the radio's output, and an rf signal generator. You can use the voltmeter in either of two ways; You can use the AC volts setting and measure the output transformer secondary voltage, or you can use the DC Volts setting and measure the AVC line. I have always used the latter, but to each his own.
You use the signal generator to inject a known, modulated, rf signal into various stages of the radio. The modulation frequency is usually a fixed 400 Hz tone. This is useful because if you try to use a broadcast station to do an alignment, the volume will go up and down as people talk, or music plays, which makes it extremely difficult to do accurate measurements.
Typically, you start by injecting the IF frequency (usually 455 KHz, but that depends on the radio) at the input to the second IF transformer. Then you adjust the trimmers on the secondary and primary for maximum output voltage from the voltmeter. When you adjust the trimmers, you are trying to adjust them so that the transformer achieves resonance at the IF frequency. Maximum output will be measured if the transformer is 'tuned' (resonant) at the IF frequency.
When that has been done, you keep the signal generator at the same IF frequency and connect it to the input to the 1st IF transformer and adjust the 1st IF trimmers in the same manner (to achieve maximum output). Usually it is best to go back and forth adjusting the 2nd and 1st IF transformers a couple of times for peak performance.
Then you move into the RF section. I always forget whether you start at the low or high end of the AM band (or maybe it doesn't matter). Say you are starting at the low end, you would usually set the signal generator to ~600 KHz, and move the dial to that frequency. Then there are trimmer and sometimes padder caps that are adjusted. In all of these steps you are adjusting to maximize the measured voltage on your voltmeter.
Finally you make adjustments for the 'other' end of the dial scale. In the case of my previous example you would now set the signal generator to 1600KHz or thereabouts and adjust different trimmers/padders.
The schematics in Riders (and presumably in Sam's as well) usually include specific instructions on where to measure, where to connect the signal generator, and the frequency output by the signal generator at each stage of the alignment.
I hope this helps
Jon
RE: Alignment question - standardtwin - 09-05-2014
Thank you for that helpful explanation.
Is it expected that most sets will drift out, or do they seem to hold, unless someone fiddles with the padders?
RE: Alignment question - tab10672 - 09-05-2014
Although I have only aligned a handful, In my personal experience, sets with seperate from the coil padders are always off, the screw type with two on top of the can seem to be off somewhat but the slug type with one on top and one underneath have been good as to not benifit from aligning.
RE: Alignment question - PAradiogeek - 09-05-2014
I've always been able to get rather large increases in the AVC voltage that I measure as I go through an alignment. Thus far, I've only worked on 1930's era sets. I don't know if the fact that these are somewhat older has anything to do with that.
Good luck doing your first alignment when you get to that point.