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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 4:29 am 
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Location: Vieques, PR, USA
Oh, one other thing regarding good quality RF components.<BR>The xtal set pros can vouch for the importance of good low-loss coil forms and caps.<BR>And if you've read up on the Scott "World's Record" TRF sets of the 1920s, he attributed much of the performance to high quality components. The claim to fame was based on his hearing his Chicago BC station on several occasions while in New Zealand.<P>-Bill M<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 6:22 am 
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This is a very interesting thread! Everyone seems to have encountered at least one "dog" radio; mine is a Sentinel 276P, an AC/DC/battery set from 1942. The original loop antenna was missing, and no substitute that I have tried works properly. The set has good sensitivity at the top end of the broadcast band, but is lousy below 1200 khz or so. I'm about ready to try an adjustable oscillator coil, to see if I can get this beast to track.<P>Some Zeniths are pretty hot; I restored a 1950 Zenith AA5 for a freind of mine and was astonished at its sensitivity. The IF transformers must have been good.<P>Tim <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 6:33 am 
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Tim, I suggest that you leave the osc coil alone, and add or subtract turns from the loop to get the strongest signals at the lower end of the dial, down around 600 or 700. Once the low end is working right, then the high end should be adjustable with the trimmer. <P>------------------<BR>Dennis


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 7:56 am 
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Most of the aa5 i have had all worked very good after a proper alignment . I do have an Olympic<BR>That does not have very much volume on weak stations .<BR>Alignment by the book does not always work the best if you have done enough AM radios you can do them easy & proper without equipment<BR>I learned about using IF adjustments to move the low end tracking here on this forum and it has saved a few radios & worked 100% . <BR>I did fix an RCA that was way off by adding a capacitor off the osc. coil .<BR>I dont know where you guys are getting your Zenith aa5`s but every one i ever had was top of the line for pulling in stations <BR>Never ever had a dog Zenith . <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 2:24 pm 
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Location: Tucson, Arizona
Let's not forget that some sets use slightly different IF frequencies, such as 456 KC or 465 KC. I know people who always use the good old 455 KC on every radio they align, insisting it is close enough. However, if a radio was built with a 465 KC IF, and tracked correctly at the low end when new, it might not track correctly if later aligned to 455 KC. Signal generator dial accuracy is also a factor .<P>------------------<BR>Bill S.


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 5:55 pm 
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Hi, Dennis... Thanks for the tip! Instead of trying another oscillator coil. I'm going to try a "Vari-Loopstick" adjustable antenna coil (remember those?) in place of the missing loop antenna, to see if the low end will come in. BTW, the IF alignment is right on.<P>Tim <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 8:54 pm 
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Location: ID 83301
I also read somewhere the coils in an IF can might slide down the form they are on due to the heat melting the wax just enough over the years and greatly affect the alignment .<P>Try without the signal gen & stuff you will be suprized . <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sat 07, 2004 9:33 pm 
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Location: Northport wa. USA.
I have a Philco PT-2 from about 1942 that works real good. I tend to agree that these sets seem to vary all over the place in terms of performance.<P>------------------<BR><BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sun 08, 2004 1:26 am 
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ken, what you are talking about doing, adjusting without knowing IF is correct freq is exactly how you can get screwed up. I agree it will make it better,wherever in the band youy adjust it, but not at both ends of dial;You may be lucky, and have one that is on the corerect IF,and it works that time. It will not work every time. As far as Zeniths go, if that is your favorite, they all work well,especially if you have nothing to compare them to. I used to like them too, but the problems you run into on them really are engineering shortcomings. Try a Philco dual triode converter, with two IF's, in a little table top radio..it will eat any big Zenith alive.One I had (1942)gets the BBC in Boston with no antenna at all, just like it was a local station. Anyway, we all form opinions, and that is fine, but that is all they are.It may be that Zenith IF's are repairable, as Mr Detrola suggests. I am going to look into that.<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sun 08, 2004 1:33 am 
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Location: Pocasset, Cape Cod, MA
Bill mentioned coil-form losses, but no one has said anything about the phenolic insulators used in variable capacitors. Just as with the coil forms, these insulators can absorb moisture and kill the Q. Measuring a few old ones on a Q meter is instructive. As noted, the crystal-set boys are up on this sort of thing, since they can't make it up with more stage gain.<P>Poor rotor contacts can mess up the Q also, and it wouldn't surprise me greatly to find that tube socket insulation can make a difference.<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sun 08, 2004 1:41 am 
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Assuming we are talking simple single-band AA5 receivers... And that the mechanical dial point alignment is set at the stop...<BR> <BR>Adjusting the IF frequency high or low to achieve tracking is viable for several reasons:<P>First is "arithmetic selectivity", 20 kHz of tracking error will go virtually unnoticed at 1600 kHz, but will be very noticable at the low end of the dial where the RF stage is much more selective. Moving the IF is the only means to correct tracking without resorting to mechanically bending the variable capacitor plates, or playing with the coil windings... It is also very resersible. Since these sets universally have a trimmer to set tracking at the high end of the band which will easily compensate for small shifts in the IF center frequency of 10 or 20 kHz.<P>All of these steps can be done by using local stations as calibrated reference points for alignment by ear if need be--something that can be done if you know what you are doing. To that extent I agree with Ken.<P>Peter<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Sun 08, 2004 1:42 am 
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I understand what Ken is describing because I've had to do it on occasion also. If you've got an unresolvable oscillator tracking error sometimes you can push the IF off 20 kcs or so and get it to track better.<BR>Its a mixed bag of snakes, though, because you still need to get the ant/rf stage to track to the new freq as well. But if the tracking error is creating more problems than being 20kc out of whack at the IF then it is a workaround.<BR>-Bill M <P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Mon 09, 2004 2:40 am 
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My point is that the oscillator fequency, with a smaller osc gang, is set mechanically to follow a curve with specially shaped plates..it is not linear, as the delta C in pF for 1005 to 2605 kc,and per degree turn of the cap, (osc range in AA5) cannot be the same as 550 to 1600, with one fixed(and different!) L value (set by low end/gang closed)in each case; Thus the smaller gang on later AA5's with a differing rate of change for the higher frequency/smaller C change; so if it is wrong (the difference)at the low end,and you move IF to get it to work there, changing the IF will mean the curve will start off displaced and not keep a constant 455 difference from the antenna tuning; you can fix the high end with the trimmer, true, but now you may have a big gap of low sensitivity in the middle. Almost every AA5 that has been hit with the golden screwdriver,when it is not working right, (align IF by ear at 650kc, then trim at 1500kc)has exactly that characteristic..nothing to talk about from 800 to 1000, or MUCH weaker in pickup than 1300-1600. There is no reson I know of except something like this why a radio picks up great at the trimmer setting and is a dog in the middle. After all, the exact same tubes parts etc are working for you in both cases; AVC may be hiding stuff as well. Maybe AVC should be replaced by -3V when doing this? discussing this ought to lead to understanding why; maybe putiing a small ferrite or brass piece(as the case may be )into or near the osc coil will make it right with the gang closed(check with counter-1005kc); that will put the tracking curve in the right place...and adjust the antenna resonance to match ,455 lower than the osc. (550) Now ,you got somethin. Next one is getting checked that way...I would add that Philco 70 and 90 with the low end trimmer respond beautifully to rocking the gang at low end , and setting it, no "weak in the middle on those"... the non AVC 70 is exceptionally sensitive in that regard.<P>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Mon 09, 2004 3:46 am 
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Location: Vieques, PR, USA
John,<BR>What you describe is exactly my point also. I wasn't referring to one that tracked correctly at the IF freq and was just being moved 20kc away in hope of some magic improvement. I was referring to those that DON'T track correctly at say 455kc but DO track better at say 435kc.<BR>Indeed there's a compromise but the general idea is to make a poorly functioning radio work better than it did if indeed the parameters that affect the tracking have changed over the years and are causing a problem.<P>-Bill M<P><BR>------------------<BR>


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Mon 23, 2004 8:58 am 
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Location: Burbank, CA and Thailand
Fantastic thread and full of xlnt info, thanks gentlemen.<P>This is a bit off topic but as a kid I DX'd longwave with a Philco 39-40. (Hardly an AA5!) Although I've read that that model was a step down in quality for Philco at the time, it was amazingly sensitive and with an external loop antenna, pulled in countless 250 watt (and less, if you are familiar with pre-sunrise authorization powers of 73 watts and such) broadcast stations from thousands of miles away.<P>Maybe it was the coils. Interesting comments about coil quality here. I can believe that they'd make a big difference.<P>I bought another 39-40 a few years ago. So far it's just been decoration, but one of these days I'm gonna give it a no-compromise restoration, and see what it can do!<P>Thanks again for all the great info here.<P>David<P>------------------


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 Post subject: AA 5 performance/"Lemons"
PostPosted: Feb Mon 23, 2004 5:05 pm 
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Location: Cedarville OH USA
Just want to add another $0.02 worth on contaminated phenolic material in tuning caps. I had been banging my head against the wall with a Crosley 63TA that had a totally dead oscillator. First thing I found was an open oscillator coil which I very carefully fixed and rewound. In desparation I took the tuning cap out and inspected it--after noticing the wires had been soldered with acid core solder and there was a lot of spatter I measured capacitance which was OK on the BC side and zip on the oscillator side. Ohmed out at 420K from oscillator stator to rotor. Cleaned with Lime Away and blew dry with wife's blow dryer. Fired right up afterward!.<P>------------------<BR>


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