Hey all, the osc coil has a short? in this where the am band has quit except for a little bit at the high end of the dial, all the other bands work as does the push button tuning, if I put my fingers on the coil I can get the whole am band to work, my question is is there a way i can use a cap or something to compensate for my fingers short of trying to re-wind this? or if someone would have a old one lying around they might want to sell? any ideas would be gladly apprecaited.
Thanks
Elton

What tells you that it is shorted? Do resistance readings disagree with those given in the schematic? Unless you know that it is shorted, this sounds more like other components failing in the oscillator section such as leaky condensers, drifted resistors, or a bad oscillator tube. Usually when these components start to fail, the low end of the band is the most difficult to receive.

Thomas, I really am not sure it is shorted, just one day out of the blue while playing it sounded like a little electrical pop and then the am was gone except from about 1400 - 1600 as I said if I place my fingers on the windings the band will pop (sounds just like when it poped out) and start working again, I have checked resistors, and caps ( except Micas not sure you can check these without replacment) and everything else in the circuit including the band switch I checked the resistance of the coil and it apears to be correct according to schematic but are my fingers adding capacitance to the circuit? is this a sign it could be a cap somewhere maybe a mica?
Thanks
Elton
:What tells you that it is shorted? Do resistance readings disagree with those given in the schematic? Unless you know that it is shorted, this sounds more like other components failing in the oscillator section such as leaky condensers, drifted resistors, or a bad oscillator tube. Usually when these components start to fail, the low end of the band is the most difficult to receive.

Could be that the coil is open -or- shorted. Certainly an open coil is an easy check. Check for shorts between the different parts of the coil. If the coil is all one with taps, disconnect each part of the coil and test separately. I don't think that the oscillator circuit would work at all with an open coil, but it could. Your finger could be providing enough capacitance for the grid coil, if any, to function, if it happens to be open.

A gassy or weak tube can cause it to "pop" out of operation. A leaky or shorted condenser, whether mica or paper, is easily tested on your multi-meter on its most sensitive setting. Remove the condenser from the circuit first. An open condenser is, however, only easily found by replacement.

Thomas

I checked the resistance of the oscilator coil and the schematic calls for .3ohms my coil reads.6 ohms would this be enough to throw off the AM to stop working? if so is it something that can be repaired? it is covered in wax ,or could I possibly compensate for this with a cap to bridge it to bring it into operation?
finding a replacment could be impossible, or could a generic replacment be used in its place?
Thanks for your help
:Could be that the coil is open -or- shorted. Certainly an open coil is an easy check. Check for shorts between the different parts of the coil. If the coil is all one with taps, disconnect each part of the coil and test separately. I don't think that the oscillator circuit would work at all with an open coil, but it could. Your finger could be providing enough capacitance for the grid coil, if any, to function, if it happens to be open.
:
:A gassy or weak tube can cause it to "pop" out of operation. A leaky or shorted condenser, whether mica or paper, is easily tested on your multi-meter on its most sensitive setting. Remove the condenser from the circuit first. An open condenser is, however, only easily found by replacement.
:
:Thomas

Your coil is not likely shorted. That little discrepancy in resistance can be caused by a slightly poor connection at any point on your meter leads. Don't worry about it. Something else is wrong. Is one part of the coil perhaps shorted to the other? If the coil is a single layer, (the coil I'm familiar with is about 3/4 inch in diameter and about 3 inches long) then there is no way for a short to occur between coils.

Thomas

Thomas, the problem I beleive is where the coil is wound the thickest, is about 1/8th inch tall and about that wide that is where I can place my finger and the am will pop back in, could it be shorting out in this area? The rest of the coil is as you say 1 layer, this thing has me stumped, the tubes are good the only thing I have not done yet is replace the micas as all of them test as they are open ( no deflection on the meter even with a digital has no indication ) so I guess that is my next step.
:Your coil is not likely shorted. That little discrepancy in resistance can be caused by a slightly poor connection at any point on your meter leads. Don't worry about it. Something else is wrong. Is one part of the coil perhaps shorted to the other? If the coil is a single layer, (the coil I'm familiar with is about 3/4 inch in diameter and about 3 inches long) then there is no way for a short to occur between coils.
:
:Thomas

Micas are small, and will not deflect an ordinary meter of any type. Without a condenser tester, there are two "home brew" methods you may use. One is to use the 250 volt scale on your meter and to use a 110 to 250 volt DC supply. Connect your meter to the DC supply appropriately, and place the condenser in question in between one of the connections. Careful! You can get shocked, so apply the power after all connections have been made. Now watch the meter when power is applied. Even with small micas, you should be able to see some deflection. Test against known good condensers of the same value. If a new condenser of the same value deflects the meter, then the old one should, too. Since you are using high voltage, you are more likely to see shorts and arcing as well. Arcing would be represented by a jumping needle. This would be heard in the radio as crackling.

The second method is to use your signal generator as a signal source for a working radio. Keeping the generator at a low output so as to not actuate the AVC, you may place a condenser in series with the generator and check output at the speaker. Test against a known good condenser in new condition. Unless your radio is adequately shielded, however, this test may be inaccurate due to the signal getting to the radio through the air.

Both of these test methods, especially the second one, are a little over the top, however, and so you are probably better off just purchasing new condensers and trying them, or purchasing a condenser tester.

Thomas