I have about 20 of these transformers I got a deal on from a surplus center that I have been using for preamps. The issue is that they tend to be on the buzzy side if I do not modify them a bit with something to damp the resonance in the top bell. (Through hole design). I am using maybe 1/15th the current capability, so they tune all day long at just over room temp.
I was using hot glue to fill the top bell and then pressing them together, but: A) hard to measure if I have enough or to small of an amount. B) it does not really seep into the windings the way something more fluid would.
So, I went to the grocery store and bought some paraffin wax. I always make a high density foam gasket when I put the top bells on for additional damping, so they are sealed for the most part. I flipped the transformer over to the bottom and cut away the bottom paper exposing the leads and used a heat gun to melt and drip the wax into the transformer. Voila! Much quieter than hot glue, but at a lower melting point. I'm not worried about the operation heat, but down south here, a garage can get almost as hot as the melting point of the wax.
After my drawn out explanation of what I need it for
what does Cary use to pot their transformers which run significantly hotter than the ones I use? I found some microcrystalline waxes that melt at a hotter temp, but the Cary wax looks more like a bees wax with something added maybe?
Thanks for any assistance!
Blair
I was using hot glue to fill the top bell and then pressing them together, but: A) hard to measure if I have enough or to small of an amount. B) it does not really seep into the windings the way something more fluid would.
So, I went to the grocery store and bought some paraffin wax. I always make a high density foam gasket when I put the top bells on for additional damping, so they are sealed for the most part. I flipped the transformer over to the bottom and cut away the bottom paper exposing the leads and used a heat gun to melt and drip the wax into the transformer. Voila! Much quieter than hot glue, but at a lower melting point. I'm not worried about the operation heat, but down south here, a garage can get almost as hot as the melting point of the wax.
After my drawn out explanation of what I need it for
what does Cary use to pot their transformers which run significantly hotter than the ones I use? I found some microcrystalline waxes that melt at a hotter temp, but the Cary wax looks more like a bees wax with something added maybe?Thanks for any assistance!
Blair
I'd guess that usual potting involves some resin or epoxy, maybe even with enhanced thermal conductivity. I'd be hesitant to use wax, as it has a rather low fire point.
Here's a short piece on potting transformers with resin: Designing Ampiifiers, Part 3
And something from this board as well: http://www.diyaudio.com/forums/tubes-valves/8022-potting-transformers.html
And a story from Cary: Cary Audio Design - Transformer Potting
Here's a short piece on potting transformers with resin: Designing Ampiifiers, Part 3
And something from this board as well: http://www.diyaudio.com/forums/tubes-valves/8022-potting-transformers.html
And a story from Cary: Cary Audio Design - Transformer Potting
Parafinwax melts already at 37 degrees Celcius. You need stearic acid, if you have the right stearic acid it melts at 70 degrees celcius
I have about 20 of these transformers I got a deal on from a surplus center that I have been using for preamps. The issue is that they tend to be on the buzzy side if I do not modify them a bit with something to damp the resonance in the top bell. (Through hole design). I am using maybe 1/15th the current capability, so they tune all day long at just over room temp.
I was using hot glue to fill the top bell and then pressing them together, but: A) hard to measure if I have enough or to small of an amount. B) it does not really seep into the windings the way something more fluid would.
So, I went to the grocery store and bought some paraffin wax. I always make a high density foam gasket when I put the top bells on for additional damping, so they are sealed for the most part. I flipped the transformer over to the bottom and cut away the bottom paper exposing the leads and used a heat gun to melt and drip the wax into the transformer. Voila! Much quieter than hot glue, but at a lower melting point. I'm not worried about the operation heat, but down south here, a garage can get almost as hot as the melting point of the wax.
After my drawn out explanation of what I need it for
Thanks for any assistance!
Blair
If you check on the web for suppliers to candle-makers, there are three grades of paraffin wax with different melting points. The stuff generally used for canning is probably the lowest melting grade.
Edit - a brief look at one candle maker's site listed their highest melting wax at 163F - you might find some higher melting waxes with a longer search.
Edit - a brief look at one candle maker's site listed their highest melting wax at 163F - you might find some higher melting waxes with a longer search.
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Beeswax is what Cary uses, it is not flammable. I use it too this is where i get it
Pure Beeswax, Dadant & Sons Beekeeping Supplies and Candles
Best of luck
Peter
Pure Beeswax, Dadant & Sons Beekeeping Supplies and Candles
Best of luck
Peter
Historically, varnish is used but it is not just the standard marine spar varnish you'd paint on wood. It is special kind made for transformers. They usually apply it in a vacuum. The Vacuum pulls the air out from between the wires and lets the varnish in. Then the transformer is baked in a low oven. The other historic method is to use wax but it makes a mess if the transformer ever overheats and is not cheaper than varnish
Beeswax, as far as I've seen, melts at a lower temp than the microcrystalline wax previously mentioned - this might not be much of an issue for an output transformer, but important for power transformers. Beeswax chips are also readily available, and may be cheaper than the slabs. Anything that damps the output transformers and keeps them from singing is probably a good idea. Mine always sing when I do a square wave test.
Varnishing is also a good idea it displaces air from the windings (improving breakdown voltage) and preventing the lams from rusting, but it doesn't damp the transformers completely. Dolph's make a good series of varnishes for transformers. I use BC-359 at work for SMPS transformers. Transformers using paper in between windings should be varnished, as the paper can be hygroscopic otherwise, and will have a low thermal rating without varnish impregnation.
Varnishing is also a good idea it displaces air from the windings (improving breakdown voltage) and preventing the lams from rusting, but it doesn't damp the transformers completely. Dolph's make a good series of varnishes for transformers. I use BC-359 at work for SMPS transformers. Transformers using paper in between windings should be varnished, as the paper can be hygroscopic otherwise, and will have a low thermal rating without varnish impregnation.
I'd not use the wax.
If it is just the top bell, then try a "gasket" or inner coating of silicone rubber.
If you have buzz, also try the circuits that take DC offset off the AC mains.
The wax is going to make the xfmr run hotter in general.
For lamination buzz or winding buzz, a vacuum dip in the varnish used for motor winding is ideal. You can pull enough vacuum in a used pressure cooker, although you have to modify the overpressure valve (usually a rubber bit in a hole) in it - but that is simple. It doesn't take much vacuum to pull the air out of the transformer. I am told by my local pro motor rewinding shop that they don't do the vacuum part when they dip. The stuff they use is rather thin looking. Big tank, in the floor!
If it is just the top bell, then try a "gasket" or inner coating of silicone rubber.
If you have buzz, also try the circuits that take DC offset off the AC mains.
The wax is going to make the xfmr run hotter in general.
For lamination buzz or winding buzz, a vacuum dip in the varnish used for motor winding is ideal. You can pull enough vacuum in a used pressure cooker, although you have to modify the overpressure valve (usually a rubber bit in a hole) in it - but that is simple. It doesn't take much vacuum to pull the air out of the transformer. I am told by my local pro motor rewinding shop that they don't do the vacuum part when they dip. The stuff they use is rather thin looking. Big tank, in the floor!
A word of caution
Sometimes if you dip coils in varnish the outside gets a skin on it and the inside remains liquid for months and sometimes never dries out. Also some varnishes contain solvents that can damage the coating (Enamel)on the copper wire used and cause flash over.
I have used silicone adhesive as a coating inside end bells to stop mechanical hum and noise. Also I have used wax inside guitar pick ups to stop the micro phonics when close to a speaker cab. It worked well but there is no heat involved in operation.
In years gone by what was the black/dark brown tar like substance used in the paper wound Tx's? If the Tx overheated it would ooze out and then set again.
Regards
M. Gregg
Sometimes if you dip coils in varnish the outside gets a skin on it and the inside remains liquid for months and sometimes never dries out. Also some varnishes contain solvents that can damage the coating (Enamel)on the copper wire used and cause flash over.
I have used silicone adhesive as a coating inside end bells to stop mechanical hum and noise. Also I have used wax inside guitar pick ups to stop the micro phonics when close to a speaker cab. It worked well but there is no heat involved in operation.
In years gone by what was the black/dark brown tar like substance used in the paper wound Tx's? If the Tx overheated it would ooze out and then set again.
Regards
M. Gregg
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Modern "enameled" wire is coated with something that is not enamel at all. Almost all of it for the past 50+ years is impervious to almost all standard solvents. Fwiw. The newer stuff is one of several high-temp polymers, afaik.
The stuff used for motor windings now is not classical "varnish" with a solvent to dry. It's some sort of synthetic chemical brew that drys/hardens due to a chemical change that goes all the way through the material. So the skinning doesn't happen as it might with typical varnishes.
The stuff used for motor windings now is not classical "varnish" with a solvent to dry. It's some sort of synthetic chemical brew that drys/hardens due to a chemical change that goes all the way through the material. So the skinning doesn't happen as it might with typical varnishes.
Most wire these days is nylon + polyurethane coated in some combination. I found out in the mid 70's that this coating was impervious to most solvents, including paint stripper (nasty at the time, with lots of methylene chloride). A tech at my job at the time showed me that the coating was solder-strippable, and it was a revelation!
So, you have the ancient NOS wire with formvar/varnish insulation (friction strip with knife/sandpaper) nylon-polyurethane or polyester (polyester is far less common, but both types are solder strippable), and the really hard-core polyimide/polythermalize insulation that must either be laboriously scraped off or removed with a really nasty stripper chemical that absolutely must be removed after it has done its thing. Polythermalize is such a
PITA that I usually don't bother to buy it. If you have access to a CO2 laser stripper, that would be a viable option, but I haven't seen one of those since my summer intern days with Martin-Marietta back in the early 70's.
So, you have the ancient NOS wire with formvar/varnish insulation (friction strip with knife/sandpaper) nylon-polyurethane or polyester (polyester is far less common, but both types are solder strippable), and the really hard-core polyimide/polythermalize insulation that must either be laboriously scraped off or removed with a really nasty stripper chemical that absolutely must be removed after it has done its thing. Polythermalize is such a
PITA that I usually don't bother to buy it. If you have access to a CO2 laser stripper, that would be a viable option, but I haven't seen one of those since my summer intern days with Martin-Marietta back in the early 70's.
You have me thinking,
I have never tried this stuff, I have some clear two part resin and hardener used for model railways to make water in ponds and rivers. It runs and gets everywhere (high creep) and sets like concrete. It is like clear plastic when it sets. Not sure about the insulation value though.
<<perhaps the thermal conductivity might not be good. I have used the two part black potting compound in the past with good results.
Just don't expect to repair it if it goes open circuit!!
Regards
M. Gregg
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