Roller Inductors

[W8HDU]

Good to know about the silver nitrate. As I said, the whole idea of plating the coils needs to be looked at carefully. I don't want to get into a situation where there is undo risk to me, family, or environment.

On the fixed coils I can always clean the copper in a soft acid bath then lacquer to keep them looking good.

[K9FV]

Yes. It is far more difficult than people realize to build a good roller, or to get one that has enough inductance for 160 and still works above 20 meters well.
73 Tom

Thanks for all the GREAT info Tom - and others who have posted. The statement above explains to me why I had such good luck with a dual roller inductor balanced tuner I was playing with would tune low bands pretty good, but I had a real problem with the higher (above 14 mhz) bands.... Also VERY touchy on some bands where it worked. This has been a VERY good thread.

RE the silver plating - Steve Katz mentioned some tests he ran and didn't feel sliver plating was really worth the hassle and expensive... still looks good. {grinning}

73 de Ken H>

[WB9JTK]

Silver nitrate is very, very dangerous.Doctors used to use a silver nitrate pen to burn off small warts

I guess the silver nitrate they put in our eyes when we are born is very diluted ? Maybe they don't do that any more.

Has anyone ever read a study of the effectiveness of plating at various frequency ranges? I wonder if a copper coil that has turned green is any less efficient at low frequencies.

And how thick does a silver plating have to be ?

[W8JI]

I guess the silver nitrate they put in our eyes when we are born is very diluted ? Maybe they don't do that any more.

Has anyone ever read a study of the effectiveness of plating at various frequency ranges? I wonder if a copper coil that has turned green is any less efficient at low frequencies.

And how thick does a silver plating have to be ?

I ran into this years ago designing HF coils.

Katz is correct, the plating makes no measurable difference at all in HF losses at any reasonable plating depth. It makes the coil look pretty, it makes a pressure connection easier to maintain, but it does not increase Q or reduce heating a measureable amount unless it is at a low pressure connection point.

We tried to get platers to plate thick enough for HF and it would have cost us hundreds of dollars. I may not recall the exact numbers now but it seems to me we could get only a few ten thousandths of an inch plating from a silver plater using expensive heavy plating and we needed about 20 times that amount to start making a worthwhile change.

The thing that really kills it is as the material is a little more resistive on the surface the current just moves deeper. The better the conductivity the thinner the skin depth. So even if you let a coil get all corroded or plate it with something like tin, it doesn't change as much as you expect.

Now VHF or UHF is quite different, as are low pressure mechanical connections in the connection itself. Silver plate can help there.

73 Tom

[W8HDU]

Is there anything on the market, other than De-Ox, that could be put on a clean copper coil to hold the color, yet still allow for good connections?

My experience with roller coils is that the silver plating is better if you're adjusting them with a roller or clip. When the copper starts to get that greenish look, then there is resistance in the connection of the tap.

So what would be a safe alternative?

[W8JI]

Is there anything on the market, other than De-Ox, that could be put on a clean copper coil to hold the color, yet still allow for good connections?

My experience with roller coils is that the silver plating is better if you're adjusting them with a roller or clip. When the copper starts to get that greenish look, then there is resistance in the connection of the tap.

So what would be a safe alternative?

The only thing I'm aware of is a light silver plate to retard the tarnishing.

You can clear-coat copper but that prevents making a good pressure connection on movable taps.

There are rub on silvers, like silversmith for restoring old siverware.

[KG4CGC]

Thanks for all the information everyone.
I have chosen to use a switched inductor in a homebrew tuner. I just need to decide on proper switches.

[W8HDU]

The only thing I'm aware of is a light silver plate to retard the tarnishing.

You can clear-coat copper but that prevents making a good pressure connection on movable taps.

There are rub on silvers, like silversmith for restoring old siverware.

Cool Amp is a product that works well, but it's a lot of work to coat a large coil.

[KL7AJ]

Thanks for all the GREAT info Tom - and others who have posted. The statement above explains to me why I had such good luck with a dual roller inductor balanced tuner I was playing with would tune low bands pretty good, but I had a real problem with the higher (above 14 mhz) bands.... Also VERY touchy on some bands where it worked. This has been a VERY good thread.

RE the silver plating - Steve Katz mentioned some tests he ran and didn't feel sliver plating was really worth the hassle and expensive... still looks good. {grinning}

73 de Ken H>

Used to be that every broadcast transmitter had silver plating. Nowadays, they use a type of inversion process (sort of like anodizing) to prevent corrosion.

In FM broadcast transmitters, silver is still sort of important, but not for MW or HF.

The cost of silver is way overinflated...since it's usually only a few molecules thick. You might have a GRAM of silver in a whole broadcast transmitter...but they charge for it like it's platinum. Go figure.

Eric

[KB5GT]

If you can't turn rotary inductors with wheel contacts at full power, how can I tune my Henry amps>
Ed