[GarySP]

Hello everyone. I decided some routine upkeep is in order on my model 20, and with it being too cold outside to do anything it seemed like the perfect time to climb into it. I'm planning on rewinding my RF coils first off. They work now, but everything I've read here says I'm living on borrowed time.
Second, I plan on replacing my power cord to the set. It's very brittle. I'm leaning on replacing it with a three conductor cord to provide the necessary ground I need for the set. Found some period-correct three conductor cable, but having a difficult time finding a suitable wall plug for the line. Anyone have any suggestions? This leads to the next question. Since I will be using a 'dirty' ground I thought I would install some pre-set filtering. I'm considering adding Y line to ground filter caps, and an X across the line cap to pre-filter the line voltage. I can get safety caps for this. Since I'm not as experienced in electronics, I'm asking your opinions on this. Do you think this filter arrangement will be enough to knock down any RFI I might encounter on my service? Also, what value do you think would be adequate? Last, and probably most daunting, I'm thinking of re-coning my type K speaker. I'm considering doing this myself. Anyone know a good source for speaker cones for this set? My speaker currently is more patches than original cone, and I'm hoping a new cone will improve its' performance. I've also thought of replacing with a PM speaker, if this ends up being cost prohibitive. I'm not so concerned with being original authentic. This was my grandparents' radio. My grandfather was quite the tinkerer, and would probably have done upgrades to the set if they would enhance its' performance. I am making every effort to keep the cabinet original, but the inner working that won't be seen can be modified as needed. Thanks in advance for the help and suggestions. Take care, Gary

[morzh]

1. I would not touch coils if they work. Your borrowed time might be longer than any of our lives that we have left.
2. Chord is a good idea.
3. What is dirty GND? How is it dirty? If it is dirty, your Y is gonna hurt you not help you.
4. typica vlues for X is 0.1 to 1 uF, and if it is before the switch on the power side then install a bleed resistor across. Otherwise no resistor needed.
5. Typical Y is up to 3nF, but if you have isolation and no touch of chassis is possible 10nF is OK too.

[GarySP]

Hi morzh. By 'dirty' ground I mean not a dedicated ground rod without contact to the rest of my house electrical circuit. I had been led to believe that RFI from other sources in the house could use the existing ground wiring as sort of a highway to the radio. Since it is impractical for me to drive a ground rod into my yard and use it exclusively for the radio, I'm going to use the ground spade of the three wire plug to complete the circuit through my home service. This will allow me to have a ground regardless where I use the radio in my home. Appreciate the info. Take care, Gary

[Phlogiston]

What Morzh said.

X and Y filters don't help much with the line hash form most of the noise makers we have today.

It was suggested that they may help reception in providing a ground for the antenna coil. Sounds like an interesting idea, but I tried it on a Zenith the other day, one which I had removed them from entirely. It did not seem to help the signal or the noise. Your result may vary.

[tab10672]

I know from experience, when you use the ground spade of an outlet you will get alot of interference from other electrical items in your house

[GarySP]

Okay, we seem to have beat the X-Y filter issue into the ground. Perhaps just plugging the set into a good surge protector might be worth trying. Anyone have any ideas on my other questions in the thread. Thanks for the replies. Take care, Gary

[tab10672]

As for the speaker cone, my 20 has the center cone glued to the outer ridged/flexing ring, if the outer ring is ok I have used black construction paper cutting the inner cone out leaving a 1/4" lip on the spider and outer rim for glue, then I cut the paper from the side into the center pulling it in like making a funnel, lay it inside the speaker and let it unfold to fit, mark along the line you cut, cut off excess leaving a 1/4" lip to glue to itself, glue it to both inner and outer lips and paint it with lacquer to stiffen it. I have done this on a 20 and 70 and as long as the outer ring is not damaged it looks factory when finished and works fine.

[GarySP]

That's a great idea!! Would have never thought to make a cone. My flex edge and paper around the spider are in decent shape, so should be worth a try. All else fails, I'm no worse off than I was beforehand. Thanks for the tip! Take care, Gary