Hi All
One of my BGW 750s transformer is emitting a predominantly 240 hz hum. I`ve researched the subject however, most solutions target DC induction on the powerline, which is not the case here as another identical, albeit younger amp on the same line is dead silent.
I`m guessing some windings have loosened over the years in this non-torroid transformer and have began to vibrate.
The transformer is securely bolted in place as are the core/winding covers.
What can be done to subdue if not eliminate this source of noise?
TIA!
One of my BGW 750s transformer is emitting a predominantly 240 hz hum. I`ve researched the subject however, most solutions target DC induction on the powerline, which is not the case here as another identical, albeit younger amp on the same line is dead silent.
I`m guessing some windings have loosened over the years in this non-torroid transformer and have began to vibrate.
The transformer is securely bolted in place as are the core/winding covers.
What can be done to subdue if not eliminate this source of noise?
TIA!
you can remove the endbells and check the center legs that could have become loose, you can wedge a small piece of wooden shims to make them tight....then you can dip the assembly in insulating varnish, air drying type is good to use...
Sometimes the chassis acts as a sounding board. Flexible mounts can help reduce noise, but ensure electrical grounding of the transformer frame is still maintained.
Are you refering to a specific varnish or would your typical polyurethane varnish commonly found in hardware stores do?
One old trick to solve buzzing transformers was to heat varnish and pop the transformer in that and leve it to dry...
the amp is pushing more than 30years old, i doubt a replacement transformer can be found....
Replacements can be found.. Check your transformers secondary supply voltages.. If need be you could tap an low voltage supply down via Zener resistor
Or use regs or if there is space add a small transformer to feed the preamp stages...
Or use regs or if there is space add a small transformer to feed the preamp stages...
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....
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😉
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😉
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....
i do make my own traffos for anything i build......been doing that for almost 40 years now....
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.
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.
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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.
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 🙂
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