Securing the winding in an output transformer may also be a good idea - I've rewound a few guitar output transformers that tested as partial shorts on the primary side, but on unwinding there are no burn marks/wires, in fact no signs of damage in any way, my theory is that the wires vibrate and rub together eventually rubbing through the insulating varnish and causing shorted turns. The transformers were dipped in varnish, but it only penetrated about 1/4 way through, I've only come across one Drake transformer like this, the others have been Dagnall.
Try using wires coated with heat set material, they are baked after winding and testing, the material fuses in situ, ensuring proper setting, use a search engine.
I'm was thinking about using neutral cure (not acetic cure) construction silicone to secure winding (to prevent vibration) by applying several thin lines over the coil on each section (1 - 4 adjacent layers). Big tubes are very cheap and easy to use. However, all of them require humidity from air to cure, and I'm not sure how long they take to cure in innermost layers, taking into account multiple insulation layers of presspan, nomex or kapton.
I'm using neutral silicone to secure winding ends with great success. It will cure, just give it 24h at least. Not sure how long for in between layers though. But paper and nomex already contain some moisture within their fibers to start the reaction.
Why neutral silicone? Because acetic silicone will react with potting compounds containing carbonate fillers, making your compound bubble and rise = nightmare.
Silicone can be used for fine airgapping as well to achieve a precise value of inductance and will shrink very little. This saves a lot of PITA when airgapping in the micron region. It will cure as well, just use your breath to condense some water vapor on the core surfaces before squeezing them using a clamp. Leave the clamp for 24h-48h.
Why neutral silicone? Because acetic silicone will react with potting compounds containing carbonate fillers, making your compound bubble and rise = nightmare.
Silicone can be used for fine airgapping as well to achieve a precise value of inductance and will shrink very little. This saves a lot of PITA when airgapping in the micron region. It will cure as well, just use your breath to condense some water vapor on the core surfaces before squeezing them using a clamp. Leave the clamp for 24h-48h.
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You have a problem obtaining varnish / potting compounds / pre-coated wires?
You need at most a liter, use a furniture varnish in a make do situation.
Silicon compounds are RTV compounds, they can have unpleasant side effects indoors.
Read up, then go ahead.
I just buy it from a seller who sells winding wire and insulation material for motor winding.
You need at most a liter, use a furniture varnish in a make do situation.
Silicon compounds are RTV compounds, they can have unpleasant side effects indoors.
Read up, then go ahead.
I just buy it from a seller who sells winding wire and insulation material for motor winding.
I did a search for Sofia, many sellers there for electrical insulating material.
Just go see the items then decide to buy them.
Just go see the items then decide to buy them.
How do you terminate winding ends, those that are not connected to other windings but to anode/HT/B+ say?
I make external terminal blocks that I DIY on phenolic boards and these are mounted on the transformer frame.
Some transformers have PCBs with holes for soldering.
Some older projects had brass tinned lugs on fiberglass.
For very fine wires <0.2mm, I make small pre-terminal pressed paper boards and glue them on the bobbin before the winding starting.
Some transformers have PCBs with holes for soldering.
Some older projects had brass tinned lugs on fiberglass.
For very fine wires <0.2mm, I make small pre-terminal pressed paper boards and glue them on the bobbin before the winding starting.
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Thanks 50AE, after struggling for years I've started doing the same thing.
I have the full operating/service manual with schematics. Are you after building one? It is a wonderful bit of kit. The ability to listen to a material or dielectric breaking down is invaluable as well as being able to test safely to 10kv. I can take some pics of the manual if you like but can't scan it. Drop me a PM with your email address if your interested. Here's a pic of the inside to whet your appetite : )
Andy.
I have the full operating/service manual with schematics. Are you after building one? It is a wonderful bit of kit. The ability to listen to a material or dielectric breaking down is invaluable as well as being able to test safely to 10kv. I can take some pics of the manual if you like but can't scan it. Drop me a PM with your email address if your interested. Here's a pic of the inside to whet your appetite : )
Andy.
Attachments
Apologies for the late reply. MG Chemicals makes an insulating varnish:
4226A – Clear Insulating Varnish
this is available through Digi-Key and Amazon. It is solvent free and works well. MG makes several other types as well as heat conductive epoxy. They provide a lot of the compounds used by the US Military. Cheers- EVMan
To the punter that complained that xylene-based varnished turned the tape adhesive to a slippery mess, I would recommend baking the transformer first to set the tape adhesive. Another approach is to use an acrylic-based tape adhesive rather than the usual tackified rubber adhesive formulation. The acrylic insulation is less likely to slip and flag when exposed to a solvent-based varnish. The important step is to bake the transformer first before varnish impregnation to set the adhesive on the tape.