Dave Plowman wrote:
In article ,
Mike Gilmour wrote:

What constitutes 'dirty' mains anyway? What about utilities signalling
systems, mains borne baby alarms, intercom systems etc, not as
invasive as Stewarts suggestion of a neighbouring welding shop but
pollution never the less. I'm way out the in country but 'scoping my
mains showed evenly spaced spikes... tracked down to an electric fence a
third of a mile away. ;-)


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.

--
Nick