38-12 quirk, alignment? - Printable Version
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38-12 quirk, alignment? - TonyJSenior - 02-23-2008
Recently recapped a 38-12, rewound a winding on the oscillator transformer and replaced the antenna transformer with a universal type. The set plays pretty well now but I noticed a odd thing with it. There are fairly strong local stations on 910 and 950. Between 910 and 950 there is just 'air noise' as to be expected. However, when tuning into 950, I can faintly hear the station at 910 as well up until the point that 950 is tuned 'dead on'. Does this sound like something potentially with alignment (IF being to 'wide')? Thanks in advance.
- Ron Ramirez - 02-23-2008
Hi Tony
If you have not yet performed an alignment of your radio, you should do so before going any further.
If you're within a mile of the 910 kc transmitter, you might experience very broad reception of that frequency. But check your IF alignment first...
- TonyJSenior - 02-24-2008
Aligned the radio this morning with my signal generator and a freq. counter I grabbed from work (to make sure the Conar 280 was correct) and looks like that was the ticket - no more '910 images on 950' - thanks!
Just curious, barring anyone in the set prior to my owning it playing with the adjustments, do these old sets generally keep their alignment somewhat? I replaced the antenna transformer with a universal type and adjusted it for max reception and don't think that would have been a problem. Only other thing I'm wondering about is the 'feedback' winding I replaced on the oscillator coil. If I were a few turns off on that, would this have thrown the alignment off?
- Ron Ramirez - 02-24-2008
Do these old sets generally keep their alignment somewhat?
No, not necessarily. As components age, their characteristics may change. This is most often seen in the case of original resistors (which tend to increase in value), and paper capacitors (which suffer from breakdown of the paper due to the acids in the paper). Coils, and that includes IF transformers, can also change their characteristics due to moisture absorption. And that does not even include some long-ago tinkerer just changing the alignment screws for fun...
Only other thing I'm wondering about is the 'feedback' winding I replaced on the oscillator coil. If I were a few turns off on that, would this have thrown the alignment off?
Yes. However, luckily for you, you are still able to get the radio aligned properly; and in the long run, that is all that really matters.