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Valvepower · 24th May 2020, 4:56 pm

Hi,

Interesting thread.

We experience noise problems with larger toroidal transformers and as part of the QA process for toroidal transformers we apply a simulated “DC” mains supply to the transformers to check their susceptibility to DC. The gadget we use is a 100-150 watt old school filament light bulb in series with a 1N4007 diode, which is switched across the mains supply and we listen for excessive noise coming from the transformer.

We have found the ‘DC’ susceptibility of the transformer lies in choice of core material and the magnetising current. We have also noticed the quality of the bonding of the transformer core has an effect on the noise.

Regards
Terry

24th May 2020, 4:56 pm	#50
Valvepower Octode Join Date: Aug 2008 Location: Rayleigh near Southend-On-Sea, Essex, UK. Posts: 1,883	Re: How much DC on your mains ? Hi, Interesting thread. We experience noise problems with larger toroidal transformers and as part of the QA process for toroidal transformers we apply a simulated “DC” mains supply to the transformers to check their susceptibility to DC. The gadget we use is a 100-150 watt old school filament light bulb in series with a 1N4007 diode, which is switched across the mains supply and we listen for excessive noise coming from the transformer. We have found the ‘DC’ susceptibility of the transformer lies in choice of core material and the magnetising current. We have also noticed the quality of the bonding of the transformer core has an effect on the noise. Regards Terry