In article ,
Nick Gorham wrote:
A well designed mains transformer will attenuate anything outside
about 50 Hz by a considerable amount - if it didn't, decent audio
transformers wouldn't be so expensive. ;-)

I have seen normal mains torroids used as valve output transformers.
Thay do a adiquate job, so they must let through (in that situation
anyway) 50hz.

I must admit to not having tested a toroidal - it's ages since I looked at
this. But if it's letting through significant amounts of 'interference'
that the normal smoothing and decoupling doesn't stop within the audio
band, I'd assume you'd hear it.

--
*The e-mail of the species is more deadly than the mail *

Dave Plowman London SW 12
RIP Acorn