A question about a Grundig 3192

[John-Jarratt]

I am restoring a Grundig 3192 and have come across the component in the photos . It is connected to pin 4 ( cathode) of the ECC85 tube. It is the component about in the middle with the wire wrapped around it next to the 47pf capacitor . I have circled it on the schematic. It is marked 9218-014. From the schematic it looks like a coil which should have little dc resistance to ground. I measure about 390K ohm's. What is it and should it be a low resistance path for DC? Thanks for any advice.

[Radio Alex]

Hello,
Indeed it is coil in the FM tuner. It seems. 390K Ohms is a quite high reading, but I would not say that there must be a problem. The coil doesn't seem to be open. I would rather say that you have a high contact resistance from you meter probe to the component. It is possible that this is caused due to flux residue or other "contmaminations" on the solder joint. I quite often had that problem as I don't have a really good probe with a sharp end that fits on my bench top multimeter.

Kind Regards
Alex

[John-Jarratt]

Thanks Alex. I'll reheat the solder connections for that component. The wire that you see wrapped around it is not connected to anything. The component is connected through a wire that travels down the middle of it. My guess is that the component is supposed to give a slight bias to the cathode to keep it above ground. If anyone has any other ideas they are welcome to give them.

[olli0371]

Hi John,

390k is a high reading for that coil. According to the schematic the anode current of the ECC85 (may be 9 mA) should pass through the coil at around 250V anode voltage (the figures are just estimatied figures according to the datasheet of ECC85) . If it should really have 390K the maximum current would be 0.6mA which is way to low.

First of all - make sure, that you do not move the components around too much as this may affect the alignment of the tuner.
I suspect, that this coil is broken. What i have seen from other radios - this kind of coil consists out of three parts:

Connection wire 1 - coil wire wrapped around a cylinder - connection wire 2

One coil wires end is wrapped around the connection wire 1 and soldered - The other end of the coil wire is soldered to connection wire 2.
Sometimes it happens that the coil wire is corroded at the end, where it was soldered to the connection wire and then you may measure high resistance instead of completely open as the broken ends still touches each other.

You can check the coil under the magnifier glass and try to find the broken wire - sometimes it is possible to repair this with a small piece of wire or just solder.

regards
Oliver

[John-Jarratt]

Thank you Oliver. There was a bad connection on the coil.