Home Forums Show & Tell Wobbulator and DFM Re: Wobbulator and DFM

#1185
cvrs
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at our past radio club meeting Elmer gave us an informative tech session , during his session he suggested that people not try to attempt to adjust the IF’s as they are not often the cause of trouble, and that many radios were better off if the radio is left with it’s IF cans not tweaked because it is possible to allign then in such a way that the radio is able to recieve stations, but at the same time, to introduce a condition where the recievable bandwidth is made so narrow that the sound quality is affected.
I have not alligned a great number of radios but in most allignment instructions, that I have gone through ( in cases where there were good instructions) it seems to call for the IF’s to be alligned first , then the bandspread and tracking adjustments follow.

Now I am trying to wrap my head around how this works. The way I understand it the IF transformers are designed to oscillate at a predetermined IF ( usually 455) Other things are incorporated into the design of the coil such as the number of turns, the spacing of the coils, the capacitance and the type of wire which may afeect the "Q" or efficiency of the coils.

ok I can mess up the reception by making it so the transformers are misalligned in such a way that they are not resonating at 455 and thus not letting signals through, but in order to change the way the coil reacts as far as the width of the range of frequencies which are passed through would I not need to also alter some other factor such as coil spacing or capacitance? I have heard that it is best to use a meter ( not volume) to peak the IF’s for maximum output , but with the volume control turned low as to not involve the AGC circut.

He may have meant to not change the capacitors in the IF cans as they could likely be (more stable) mica capacitors which are reliable and not usually replaced, as doing so could introduce problems by un necessarily replacing a good cap with one of perhaps slightly different capacitance,thus causing the above effect.

I have seen some radios that have paper caps used in the cans , and have usually replaced them as a matter of course in recapping.

I have heard that there are some capacitors which are less likely to cause issues with leakage , and I wonder if these fall into that area. caps like used in the power supply for example have lots of potential across the plates, but caps in an IF can aren’t really in a circut where much current is flowing, thus not much voltage drop across the coils in the IF cans, so perhaps this is a factor in the capacitor’s likleyness to be a failure point.

I guess a little knowlege brings more questions and , when I saw the post about the wobbulator I had to question wheather this is an instrument that one could use to aid in alligning, to avoid clipping audible frequencies?

Should paper caps in IF transformers from early thirties sets be changed ritually for leakage? or are they better left alone? Any comments/ opinions appreciated.

my delemma is that when restoring a set , I my main objective is usually to improve the performance as much as I can without attempting to redesign the circut. If I am to resist the urge to tweak the IF adjustments, how would I know if this may have made a drastic improvement in volume , reception , tone quality etc.

I am not satisfied with leaving the screws alone, this reminds me of my dad telling me not to screw with the air fuel mixture on the old outboard. I remember him so often saying "that carb has never been adjusted, don’t turn the @$## screws".. 🙂

Phil