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Antique Radio Technical Forum
Osc coil fix

Posted by Elton on 04/30/2012 21:42

: : : : : : : : : : : : : : :Sir Elton . . . . . : : : : :I only used a small strand of wire about 3/8 of inch to jump the gap, so started experimenting with caps across the osc coil and lo and behold .05 shifted the whole upper half of the dial , even the F padder will now adjust all the way to 1600! Could that small repair to the osc coil have caused the whole coil to shift? I guess I dont understand how it could : : : : :Don't think that you have any problem with your repair method of the osc coil at these low AM frequencies . . . .attempting in the osc section of an FM band receiver. . . Yes. : : :If you were shunting that extreme left coil of the BCB oscillator coil cluster, you should have TOTALLY killed the oscillator, but NOW, look at C8. : : : : :A VERY VERY rare situation, but yes, if the involved cap is C8, and being low in capacitance or leaky, that would be a problem. : : :Why ? . . . . .take note that the situation of BOTH of your J and F trimmers as WELL AS the oscillator coil being DEPENDENT upon the flow path thru a LOW RF IMPEDANCE path thru that .005 capacitor to GET TO ground. : : :In the sets design they computed .005 to be of adequate low Z at the lowest frequency of 540Khz (995 osc freq) . . . . so your found .05 value is a bit overkill for a C8 value. : : : :Sounds like you might have all wukkin' . . . . .now ? :That other ? of the use of AC line for some RF signal pick up is done on some sets, as well on up in to the FM band, where they also have done the same. : : : :Aside: : : :Back on the IF's, wonder if you had enough errant, contaminant sand particles between the leaves and micas to just keep them separated enough to be unable to compress enough to attain that added / required capacitance? : : :Now if you happened to have had too MUCH capacitance, we kn o o o o o o w s what causes that, oil contamination . . . .e.g. like WD40, motor oil etc. . . . . . time for a bath at degreaser city ! : : : : : 73's de Edd : : : : : I love to go shopping. : : : I also love to freak out salespeople. : : :They ask me if they can help me, and I say, "Have you got anything I'd like?" : : :Then they ask me what size I need, and I say, "Extra medium." : : : : : : : : : : : : : : ::Haven't re-read all the posts, but has the problem with the IFs not tuning to 455 been corrected? Is it possible sometime in the past the IFs may have been changed with some other type? :: ::Clifton :: :::::

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::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: ::::: :::::Sir Elton . . . . . ::::: ::::: ::::: :::::You say: ::::: ::::: ::::: ::::: . . . . .but higher than 900 khz the dial takes on a sort of band spread the higher it goes the worst being 1250 station coming in at 1400 and the F padder screw is out all the way , I have been checking everthing around the osc coil but nothing out of the ordinary. ::::: ::::: ::::: :::::If I read this as a 1250Khz station coming in at 1400 on the dial scale, then the situation is now that of the F padder being in need of a slow tightening up /compressing up a bit. With the then total effective maximum capacitance value of the tuning condenser at that end of the dial scale, then being increased a bit. ::::: ::::: :::::This should then eventually /progressively lower the dial scale positioning of this 1250 station to slowly being "walked" on down to 1250 on the dial scale. ::::: ::::: ::::: 73's de Edd ::::: ::::: ::::: ::::: ::::: People will believe anything . . . . . if you just whisper it. ::::: :::::Hi edd, tightening up the screw makes it spread out farther it puts 1250 above 1600 ::::Elton ::::: ::::: ::::: ::::: :::::

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::::::: ::::::: ::::::: ::::::: ::::::: ::::::: ::::::: ::::::: ::::::: ::::::: ::::::: :::::::Sir Elton . . . . . ::::::: ::::::: :::::::I‘se . . . . . b a a a a a ck ::::::: ::::::: :::::::Some reason or another, seems like that there is not enough inductance or not enough capacitance in the IF transformer(s) to pull the IF resonance on down to 455. ::::::: ::::::: :::::::The most critical resonant pair of the TWO I.F. transformers available four sets of “ winding and adjustable trimmer capacitor “ involved, is the one that is off the plate of the mixer. The tuned sets trailing, then just enhance the overall amplitude of I.F. signal at that frequency, with broadness of tuning diminishing on down the alignment line. ::::::: ::::::: :::::::Lets crunch some numbers in an evaluation, considering that the winding of that inductor/variable capacitor of that set is going to be a fixed constant , let’s use 1020 microhenry as its value. If one then sets a mica trimmer capacitor to being compressed up to ~ ¾ of its attainable max capacitance value, that will throw in ~120pf of capacitance and effect a resonance of the pair of ~ 455 Kc. :::::::Now that is ideally, what we are looking for, but what you are EXPERIENCING, is 670 Kc, so that would be reflective of that existing L-C resonant circuit having only a capacitive value of 55 pf, present to work with that fixed 1020uh winding. ::::::: ::::::: :::::::Now another aspect to consider would be the variance of the inductance factor, but that would require a dropping of the inductance on down to a reduced value of a whopping ~476 uh in order to create that tuning resonance of 670 Kc. ::::::: ::::::: :::::::NOT gonna hoppen ! ::::::: ::::::: :::::::NowI can't eyeball the wire inside of that/those I.F. transformers , to see whether the wire beig used is common 35-38 ga single or double coton covered enamelled wire OR being Litz wire. ::::::: ::::::: ::::::: If its Litz, and taking 10/46 as the norm . . . and that would consist of 10 separate strands of #46 enamelled wire clustered together and loosely twisted as a single wire and then overwound with its cotton insulator(s) covering. ::::::: ::::::: :::::::What I have seen happen on LITZ wire is the time related action of a chemical contaminant in eroding away individual strands , at a solder junction, thereby decreasing the effective inductance of the winding. :::::::This was most common back at prodiction time in the erroneous cross utilization of a soldering iron that STILL had contamination of ACID flux on it from a counter chassis operation in mechanical soldering . ::::::: ::::::: :::::::As individual conductors are eaten out of circuit , the effective inductance of the wound coil drops and frequency rises. ::::::: ::::::: :::::::As a fix, one rosin fluxes and resolders the ends of the LITZ wire to get all conductors in circuit again. ::::::: ::::::: :::::::BUT THIS could not account for the whopping 500+ uh involved here. . . . . only a 10 uh or so, if only hanging on by one strand. :::::::About the only way to evaluate for LITZ presence in the coil winding is to peel back enough cotton overwrap, aside, as to then be able to see if there is a single wire or MULTIPLE fine wires. ::::::: ::::::: :::::::Now considering that the fault is with low trimmer capacitance, how about working with the 1st IF transformer and padding in ~two ~47 / 50 pf fixed silver mica units . . . even ceramics in a pinch . . .to :::::::see if the unit will tune in closer to 455Kc. ::::::: ::::::: :::::::Also take that tip of disabling the local oscillator while aligning. ::::::: ::::::: :::::::If this works, then the question is to be figured out as to the loss of available total capacitance of the trimmers. I couldn't even see severe salt water corrosion / rust ? deposits on ALL of the individual leaves of a trimmer, in limiting its max available capacitance down that much . ::::::: ::::::: :::::::Work on that . . . . . ::::::: ::::::: ::::::: ::::::: ::::::: ::::::: 73's de Edd ::::::: ::::::: ::::::: ::::::: ::::::: Now I ask you . . . . is it all right for vegetarians to eat animal crackers ?. ::::::: :::::::Thanks Edd , Finally got the IF's to resonate at 455 I pulled them out and they were full of crud and dust , basicly I gave them a bath in contact cleaner and did check for bad conections , put it back together and it took me awahile but finally got them tuned in! BUT I still have the problem with the J and F padders, the lower half of the dial will line up great with the J padder, but higher than 900 khz the dial takes on a sort of band spread the higher it goes the worst being 1250 station coming in at 1400 and the F padder screw is out all the way , I have been checking everthing around the osc coil but nothing out of the ordinary. I found out this is a chassis 6A05R and the schematic shows the C2 cap as connecting to the third wire of the ac cord??? is this radio suppose to have a grounded ac cord?, my C2 is just connected to the antenna coil and the other end is not going anywhere. ::::::Thanks ::::::Elton ::::::: ::::::: ::::::: ::::::: :::::::

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::::::::Hi Elton,
:::::::: You mentioned rust on the IF tuning caps. It seems to me that you may have corrosion decreasing the capacitance on the tuning. If that is the case you will need to clean up the capacitors or replace the IFs.
:::::::: Corrosion is often a problem in Loctal tube sockets. That may be another possibility.
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::::::::Best Regards,
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::::::::Bill Grimm
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:::Edd your last post about increasing the capacitence got me thinking , I had to repair the osc coil because of a break on it , I only used a small strand of wire about 3/8 of inch to jump the gap, so started experimenting with caps across the osc coil and lo and behold .05 shifted the whole upper half of the dial , even the F padder will now adjust all the way to 1600! Could that small repair to the osc coil have caused the whole coil to shift? I guess I dont understand how it could.
:::Elton
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Edd Just wanted to thank you for your help The radio is now playing great , on the C2 to ac cord the schematic says it goes to the third wire on the AC cord ???? did not know there was a 3rd wire on these back in the day...
Elton

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Osc coil fix
Elton	04/26/2012 10:54
Warren	04/26/2012 12:14
Elton	04/26/2012 15:26
Warren	04/26/2012 15:55
Elton	04/26/2012 16:01
Warren	04/26/2012 17:18
Elton	04/26/2012 21:09
Warren	04/26/2012 21:14
Elton	04/26/2012 21:28
Warren	04/26/2012 21:48
Edd	04/26/2012 22:46
Elton	04/26/2012 23:04
Elton	04/26/2012 22:56
Bill G.	04/27/2012 08:54
Walter	04/27/2012 09:42
Elton	04/27/2012 09:52
Bill G.	04/27/2012 11:46
Elton	04/27/2012 11:57
Elton	04/27/2012 17:09
Warren	04/27/2012 17:39
Bill G.	04/27/2012 20:13
Edd	04/28/2012 11:36
Elton	04/28/2012 12:53
Edd	04/28/2012 14:34
Elton	04/28/2012 15:22
Elton	04/28/2012 16:51
Clifton	04/30/2012 08:50
Edd	04/30/2012 15:59
Elton	04/30/2012 21:42

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