Mechanical Transformer Hum

[Tony]

this is an EI 1000VA traffo....55-0-55 volt secondaries.....

[lanchile]

VTX-146-1000-155 - MULTICOMP - TRANSFORMER, 1000VA, 2X 55V | Newark

[Tony]

i was given a 211 tube power amp that had buzzing issues, found out that the steel bottom plate was the culprit....solved the issue by putting in an acrylic sheet 6mm thick between the bottom plate and the chassis....the acrylic was drilled to have the same holes as the steel bottom plate....now the amp is dead quiet.....mechanically that is....

[lanchile]

Glad to hear that! Case closed!

[Michael F]

Thanks for the suggestions. Replacing the transformer is not really a practical solution in this case considering the amp is still outperforming original specs.
I`m going to go the "soak in varnish" route, has anyone actually done that?
Is it as simple as dipping the transformer (minus bell) and letting it dry out for a couple of days?
Pardon my obsessive compulsiveness

[Tony]

that's the way to do it....check the center leg and bobbin gaps, shimming it with wood, i use popsicle sticks shaved to look like a wedge and then shove it in between the core and the coil former....after that, dipping in varnish.....

i do make my own traffos for anything i build......been doing that for almost 40 years now....

[Ian Finch]

Whilst dipping can be a fair compromise, it's nowhere as thorough an impregnation on larger transformers as vacuum/pressurised immersion, such as done by electric motor rewinders. With such a large trafo, I have my doubts that there will be significant benefit. IME, small coils, transformers and toroids are easiest to get results with by simple hot dipping.

Whilst heating the varnish (flammable!) is helpful, heating the transformer and fully immersing in room temp. varnish is more effective, as the cooling of the transformer then causes a small vacuum in the windings which then draws the varnish within. The temperature is not critical but around 70C is enough without causing the xylene solvent to rise above its flash point for too long or damage sleeving. This procedure also heats the varnish to lower its viscosity anyway.

Obviously this is not a household-friendly operation but if you want to go about things this way, there are safety risks and inefficiencies. With such a beast, I would contact a rewinder and ask if they wouldn't mind putting your transformer in with the next job lot and do a thorough job, so you know whether it has been done properly and with best materials or not.

[Michael F]

Originally Posted by Ian Finch

Whilst dipping can be a fair compromise, it's nowhere as thorough an impregnation on larger transformers as vacuum/pressurised immersion, such as done by electric motor rewinders. With such a large trafo, I have my doubts that there will be significant benefit. IME, small coils, transformers and toroids are easiest to get results with by simple hot dipping.

Whilst heating the varnish (flammable!) is helpful, heating the transformer and fully immersing in room temp. varnish is more effective, as the cooling of the transformer then causes a small vacuum in the windings which then draws the varnish within. The temperature is not critical but around 70C is enough without causing the xylene solvent to rise above its flash point for too long or damage sleeving. This procedure also heats the varnish to lower its viscosity anyway.

Obviously this is not a household-friendly operation but if you want to go about things this way, there are safety risks and inefficiencies. With such a beast, I would contact a rewinder and ask if they wouldn't mind putting your transformer in with the next job lot and do a thorough job, so you know whether it has been done properly and with best materials or not.

Thanks Ian. There are (were?) a couple of local/regional transformer manufacturers that may be of help.
I failed to mention in my original posting that the amp is not terribly noisy but loud enough to cause a distraction, perhaps the DIY method may be the best solution.
I will post a follow up when I`m done.

[1SaGing5]

before bolting your transformer on your chassis, try putting a rubber material on the bottom of the transformer, this is to avoid the transformer from making contact with your chassis

[amptech]

Would agree there with use of rubber spacing between transformer and chassis.