Need Help Identifying Component

9/10/2008 10:28:51 AMJohnny

On my Montgomery Ward Airline 62-9 there is a part labeled "RFC" on the schematic. It's attached to the plate of the 27 detector with a .001mfd cap that goes to ground. The other end goes through a .015mfd cap to the 100K tone control and also to the audio xsformer. Physically this part is about 1" in diameter, 1/4" thick, and has a brass center that the mounting screw goes through to secure it to the chassis. The radio was working fine except for some static through the speaker when the volume was all the way down. I found that one of the leads on this coil was within thousandths of an inch from the chassis and it was arcing to the chassis and causing the static. I fixed the problem, static went away immediately. Now sometimes after warm-up this static intermittently returns. Tap on this small coil and it goes away. Could someone tell me exactly what this "RFC" is and what can I replace it with? Thanks much!

9/10/2008 11:59:34 AMEdd

That is a Radio Frequency Choke on the plate of the combined detector / AF driver stage where there initially is RF and detected
audio combined, with just about all of the RF present initially being bypassed off to ground via the initial .001 ufd connected onto the ’27’s plate circuitry, then with that choke coil doing the final coup de grace on the remaining RF present before getting to the AF driver transformer primary. .

The unit is probably the typical 2.5 MH value, or possibly might be as low as 1MH. If you have connections to a person / lab with
L/C measurement capabilities, it could be confirmed on your old unit. .

Not sure if you might still have old insulation presenting arc-over possibilities or even arcing to any core slug materiel. .

If my problem to solve I would fire up the set again and confirm that the unit would still react to mechanical movement with a NON METALLIC object being used to flex it with, otherwise a moving metal screwdriver blade in its proximity, just might give you a “guitar pickup” effect to then be amplified. .

If the static effect is still present, for sake of test evaluation, just lift the incoming and outgoing wiring from the unit so that they can then be interconnected. That way, you would have any leakage to ground also covered…..then evaluate to see if all is quiet now.
If so, then you would be in the market for one of those old style RFC coils. .

Standing by for any feedback. . . . .

73's de Edd

9/10/2008 12:45:52 PMJohnny(65736:65732)

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:That is a Radio Frequency Choke on the plate of the combined detector / AF driver stage where there initially is RF and detected
: audio combined, with just about all of the RF present initially being bypassed off to ground via the initial .001 ufd connected onto the ’27’s plate circuitry, then with that choke coil doing the final coup de grace on the remaining RF present before getting to the AF driver transformer primary. .
:
:The unit is probably the typical 2.5 MH value, or possibly might be as low as 1MH. If you have connections to a person / lab with
:L/C measurement capabilities, it could be confirmed on your old unit. .
:
:Not sure if you might still have old insulation presenting arc-over possibilities or even arcing to any core slug materiel. .
:
:If my problem to solve I would fire up the set again and confirm that the unit would still react to mechanical movement with a NON METALLIC object being used to flex it with, otherwise a moving metal screwdriver blade in its proximity, just might give you a “guitar pickup” effect to then be amplified. .
:
:If the static effect is still present, for sake of test evaluation, just lift the incoming and outgoing wiring from the unit so that they can then be interconnected. That way, you would have any leakage to ground also covered…..then evaluate to see if all is quiet now.
:If so, then you would be in the market for one of those old style RFC coils. .
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:
:Standing by for any feedback. . . . .
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:73's de Edd
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:Thank you Edd! I will perform those checks now.

9/10/2008 2:10:52 PMLewis Linson(65737:65736)

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::That is a Radio Frequency Choke on the plate of the combined detector / AF driver stage where there initially is RF and detected
:: audio combined, with just about all of the RF present initially being bypassed off to ground via the initial .001 ufd connected onto the ’27’s plate circuitry, then with that choke coil doing the final coup de grace on the remaining RF present before getting to the AF driver transformer primary. .
::
::The unit is probably the typical 2.5 MH value, or possibly might be as low as 1MH. If you have connections to a person / lab with
::L/C measurement capabilities, it could be confirmed on your old unit. .
::
::Not sure if you might still have old insulation presenting arc-over possibilities or even arcing to any core slug materiel. .
::
::If my problem to solve I would fire up the set again and confirm that the unit would still react to mechanical movement with a NON METALLIC object being used to flex it with, otherwise a moving metal screwdriver blade in its proximity, just might give you a “guitar pickup” effect to then be amplified. .
::
::If the static effect is still present, for sake of test evaluation, just lift the incoming and outgoing wiring from the unit so that they can then be interconnected. That way, you would have any leakage to ground also covered…..then evaluate to see if all is quiet now.
::If so, then you would be in the market for one of those old style RFC coils. .
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::
::Standing by for any feedback. . . . .
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::73's de Edd
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::Thank you Edd! I will perform those checks now.
Johnny:
If that choke checks OK with an Ohmmeter, it is probably good. They seldom short. (But they do)
Lewis

9/14/2008 11:58:37 PMJohnny(65835:65732)

:Okay Edd, Ive taken the steps recommended and I still have static. No connections with LC test capability. I can move it slightly with a plastic tool and it goes away but returns later. So if replacement is necessary do I replace it with one of the "Typical 2.5MH or 1MH" chokes? They are available but of course look nothing like the one that is in the radio. It shouldn't hurt to just try a 2.5MH or 1MH to see if one works should it? Thanks!
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:That is a Radio Frequency Choke on the plate of the combined detector / AF driver stage where there initially is RF and detected
: audio combined, with just about all of the RF present initially being bypassed off to ground via the initial .001 ufd connected onto the ’27’s plate circuitry, then with that choke coil doing the final coup de grace on the remaining RF present before getting to the AF driver transformer primary. .
:
:The unit is probably the typical 2.5 MH value, or possibly might be as low as 1MH. If you have connections to a person / lab with
:L/C measurement capabilities, it could be confirmed on your old unit. .
:
:Not sure if you might still have old insulation presenting arc-over possibilities or even arcing to any core slug materiel. .
:
:If my problem to solve I would fire up the set again and confirm that the unit would still react to mechanical movement with a NON METALLIC object being used to flex it with, otherwise a moving metal screwdriver blade in its proximity, just might give you a “guitar pickup” effect to then be amplified. .
:
:If the static effect is still present, for sake of test evaluation, just lift the incoming and outgoing wiring from the unit so that they can then be interconnected. That way, you would have any leakage to ground also covered…..then evaluate to see if all is quiet now.
:If so, then you would be in the market for one of those old style RFC coils. .
:
:
:Standing by for any feedback. . . . .
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:
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:73's de Edd
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9/15/2008 10:42:17 AMCharlie(65844:65835)

Johnny, I usually find the chokes simple enough to rewind alot of them myself. I overwind them and unwrap until I match the DC ohms.
::Okay Edd, Ive taken the steps recommended and I still have static. No connections with LC test capability. I can move it slightly with a plastic tool and it goes away but returns later. So if replacement is necessary do I replace it with one of the "Typical 2.5MH or 1MH" chokes? They are available but of course look nothing like the one that is in the radio. It shouldn't hurt to just try a 2.5MH or 1MH to see if one works should it? Thanks!
::
::
::
::
::
::
::
::
::
::That is a Radio Frequency Choke on the plate of the combined detector / AF driver stage where there initially is RF and detected
:: audio combined, with just about all of the RF present initially being bypassed off to ground via the initial .001 ufd connected onto the ’27’s plate circuitry, then with that choke coil doing the final coup de grace on the remaining RF present before getting to the AF driver transformer primary. .
::
::The unit is probably the typical 2.5 MH value, or possibly might be as low as 1MH. If you have connections to a person / lab with
::L/C measurement capabilities, it could be confirmed on your old unit. .
::
::Not sure if you might still have old insulation presenting arc-over possibilities or even arcing to any core slug materiel. .
::
::If my problem to solve I would fire up the set again and confirm that the unit would still react to mechanical movement with a NON METALLIC object being used to flex it with, otherwise a moving metal screwdriver blade in its proximity, just might give you a “guitar pickup” effect to then be amplified. .
::
::If the static effect is still present, for sake of test evaluation, just lift the incoming and outgoing wiring from the unit so that they can then be interconnected. That way, you would have any leakage to ground also covered…..then evaluate to see if all is quiet now.
::If so, then you would be in the market for one of those old style RFC coils. .
::
::
::Standing by for any feedback. . . . .
::
::
::
::
::
::
::73's de Edd
::
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::

9/15/2008 1:38:59 PMEdd(65846:65844)

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Somehow I just feel that part is not your problem, as on a that old of a set the coil typically would have been wound with single cotton covered enameled wire, and having pretty good insulative properties between turns via the additional separation provided by the cotton spacing.

There would be the additional advantage if the coil was then wax soaked, or else shellac / varnish impregnated in its construction. (However, that being bad news for the rewinding possibilities, in the latter cases).

The one real answer which I did not confirm a reply to , was the lifting of the connecting wiring to the coil and then the direct interconnecting of that wiring, such as to be bypassing the use of the coil totally, and the evaluation of the set then.

That would additionally cover the latter aspect of the coil having breakdown to its core.

Have you tapped and flexed immediately adjunct components, to confirm if it might be one of them, instead ?

73's de Edd

9/15/2008 2:44:09 PMJohnny(65849:65846)

:Sorry Edd. Guess I wasn't clear in my earlier response. The radio didn't work at all when I did that test. Lifting of the leads etc. Anyway I tend to agree that the coil is not bad. What I did find this morning is another cap buried under the xsformer that I now believe is the .001 mfd cap that goes to ground bypassing the RF off to ground. I didn't see this cap earlier and now I have three .001 caps when the schematic only shows two unless I'm not seeing one on the schematic. This cap is a Sprague "MIDGET" .001. 5/8" wide, 1/8" thick, inch or so long. I replaced it and so far no static. I'm still testing because this problem will go away and then return after the radio has warmed up for 30 to 60 minutes. So far 90 minutes and no static. This cap could have been my problem if it was breaking down correct? Thanks, Johnny
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:Somehow I just feel that part is not your problem, as on a that old of a set the coil typically would have been wound with single cotton covered enameled wire, and having pretty good insulative properties between turns via the additional separation provided by the cotton spacing.
:
:There would be the additional advantage if the coil was then wax soaked, or else shellac / varnish impregnated in its construction. (However, that being bad news for the rewinding possibilities, in the latter cases).
:
:
:
:The one real answer which I did not confirm a reply to , was the lifting of the connecting wiring to the coil and then the direct interconnecting of that wiring, such as to be bypassing the use of the coil totally, and the evaluation of the set then.
:
:That would additionally cover the latter aspect of the coil having breakdown to its core.
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:Have you tapped and flexed immediately adjunct components, to confirm if it might be one of them, instead ?
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:73's de Edd
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9/15/2008 7:45:15 PMEdd(65858:65849)

Yep, that cap arcing over or leaking would certainly be amplified by the ensuing audio stages and is the more likely of the two mentioned parts.

How about taking it now and doing my usual leakage test as mentioned at the end of:

Here. . .here. . . I’m down HERE

73's de Edd

9/15/2008 11:40:38 PMJohnny(65861:65858)

:Well Edd all is quiet now. I'd rather not lift any leads again. The leads on that thing are very fragile and I already had to extend the terminal that one lead connects to because 1/4" of it broke off during the last test. Also on the 15K pot, I was able to make a solid repair on that so it's also working fine now. Your info is always so good I do print many of your replies out for future reference. Thanks again for the great help. Johnny
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:Yep, that cap arcing over or leaking would certainly be amplified by the ensuing audio stages and is the more likely of the two mentioned parts.
:
:
:How about taking it now and doing my usual leakage test as mentioned at the end of:
:
:
:
:
: Here. . .here. . . I’m down HERE
:
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:73's de Edd
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