Excuse my English, I am French.

Phil Allison a écrit le 15/01/2019 Ã* 18:13Â*:
Look165 wrote:



Once, winded and assembled, the pieces were put in a resin we call
"jaja" in France.
And then put in an under-pressurized "bubble room" for completing the
process.
When there was no more bubbles, the process was over.

** The process is commonly known as " vacuum impregnation " - completed transformers are placed in tank of resin or varnish and the air pressure reduced until all air pockets are filled.

Not always done with bobbin wound transformers but standard practice with layer wound and old style cloth insulated toroidal mains transformers plus any tranny that handles substantial voltages.

.... Phil




Resin (or tar) is there for noise suppression, mechanical fixing of the
windings and insulation improvement.

a écrit le 15/01/2019 Ã* 12:36Â*:
On Tuesday, 15 January 2019 03:24:57 UTC, wrote:

I remember a lot of old transformers, particularly the power
transformers on the old TV sets, were coated with tar. It was not a real
problem, but was kind of ugly, particularly when the wires had tar all
over them.

What was the purpose for the tar? My guess was to eliminate chattering
of the steel laminations. Yet, it seems the practice of using tar
vanished for the most part in the 70s and later. Yet I have not seen any
untarred modern transformers chatter......

I will add to this, that the most chattering I have heard from
transformers are the small ones which do NOT have bolts going thru the
core, such as filament transformers and doorbell transformers. Several
times over the years I have had people ask me why there is a noisy sound
in their basement and it never fails, it's the doorbell transformer.

This could often be fixed by squeezing the outer metal piece against the
laminations, and applying something like laquer or silicone caulk.
However, for the small price they cost, I usually just replaced them
with a new one.
Modern transformers use clear stuff for the same purpose. It stops noises & holds the windings etc in place.


NT