Grumpy
Years ago in 93 or so on a Telco fiber system by Alcatel we took severe
hits when the air conditioner came on and it was traced to the station
rectifier. The Gould rectifiers had a weld bead and when we replaced
them another make which I can't recall that didn't have weld beads the
problem went away. Its quite strange since the rectifiers floated big
batteries but a vco in system was sensitive to the spike. After doing
some research I found an explanation that I can't recall because I was
too busy with other problems and mine had gone away. Alcatel spent
several hundred thousand trying to find the problem and I stumbled on to
it by shear luck.

73
Hank WD5JFR
"Grumpy The Mule" wrote in message
...
Hmmm!

Bolts through the laminations should have insulators
(usually fiber board washers) under the heads. Just
one end will do, there's no need for them under the
nuts. But shoulder washers are best so the bolts don't
short any laminations together deeper into the core.

If uninsulated the bolt can form a poorly coupled shorted
turn and that in itself can cause noise, heating of the
core and the hardware as well as spray flux around where
you wouldn't have expected any. How bad it is depends
on the locations of the holes in the core.

A bead of weld across the ends of the laminations won't add
to the eddy currents significantly. Steel isn't a great
conductor. The weld's cross section is small and it's very
poorly coupled to the primary.

Why would a weld across the laminations let line spikes
though?




"Henry Kolesnik" wrote in
:

If you have bolts thru the lams have you torqued them to the point of
twisting them off? If you haven't you might want to loosen then and
add
some more varnish to the lams while they're loose and then torque
them.
Another possibility: Many of the transformers in microwave ovens
have a
bead of weld across all the laminations and I've seen this on
rectifiers
used in Telco applications. Keeps them quiet and I and has some
negatives like letting line spikes thru but on a filament that is
meaningless. Lam eddy currents area dead issue as I've heard that
the
old Bell Labs had accepted this practice.
I had a 30S-1 with minor buzz but when I added 100 volts to the
screen
the hum was about to drive me nuts but torquing to lams solved the
problem, I twisted off a couple of bolts.