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.

--
73
Hank WD5JFR
"raypsi" wrote in message
...
Hey all:

I tore down a transformer I got from ebay it was a Zenith TV power
transformer from days gone by. Re wound it with 17AWG wire on the
secondary and primary. It powers up my 4-1000A filament nicely with
7.25VAC from 120VAC mains. I used a penta-filar winding on the
secondary. Shimmed the bobbin in the core window with some 1/8 thick
virgin teflon. Epoxied the windings to the bobbin. This was a 240VA
transformer and now is a 83watt buzzer / 157watt filament transformer.

So what is the cheapest I can gits away with sealing these laminations
from buzzing, I used up all my epoxy sealing the windings.

73

n8zu

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.

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.

Howdy Hank,

Thanks for the follow-up! Perhaps they used a voltage regulating
transformer. I think some of the telcom rectifiers used them.
I know some mainframe computers did.

It's still a curiosity to me. Though I've seen enough occult
behavior from wound magnetic devices that I wouldn't discount it,
I'm tempted to wonder if there's another variable that was
coincident with the welded laminations.

73



"Henry Kolesnik" wrote in
:

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

Hey Grump
A transformer is one of the simplest electrical machines and pretty well
understood in the classical design but when some of the parameters are
changed we don't have much experience or investigation and probably
wont. Hot swappable rectifier modules have made transformer based
rectifiers uneconomical kinda like carburetors and fuel injection. If
you have the time, check with some of the old time designers of
transformer rectifiers. Let me now what you find out. I had some notes
but those are long gone.
Hank
"Grumpy The Mule" wrote in message
...
Howdy Hank,

Thanks for the follow-up! Perhaps they used a voltage regulating
transformer. I think some of the telcom rectifiers used them.
I know some mainframe computers did.

It's still a curiosity to me. Though I've seen enough occult
behavior from wound magnetic devices that I wouldn't discount it,
I'm tempted to wonder if there's another variable that was
coincident with the welded laminations.

73



"Henry Kolesnik" wrote in
:

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

I left out switch based hot swappable
"Henry Kolesnik" wrote in message
...
Hey Grump
A transformer is one of the simplest electrical machines and pretty
well understood in the classical design but when some of the
parameters are changed we don't have much experience or investigation
and probably wont. Hot swappable rectifier modules have made
transformer based rectifiers uneconomical kinda like carburetors and
fuel injection. If you have the time, check with some of the old time
designers of transformer rectifiers. Let me now what you find out. I
had some notes but those are long gone.
Hank
"Grumpy The Mule" wrote in message
...
Howdy Hank,

Thanks for the follow-up! Perhaps they used a voltage regulating
transformer. I think some of the telcom rectifiers used them.
I know some mainframe computers did.

It's still a curiosity to me. Though I've seen enough occult
behavior from wound magnetic devices that I wouldn't discount it,
I'm tempted to wonder if there's another variable that was
coincident with the welded laminations.

73



"Henry Kolesnik" wrote in
:

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

Howdy Hank,

I've been designing switch mode magnetics for about
thirty years now. The more I learn the less I know.
It's true that the principles are well known but the
implementation is a morass of compromises. At the
power level many of my designs operate at, second
and third order effects can suddenly become serious
and unexpected design complications. Some people
enjoy puzzles. I guess that's why I like designing
this sort of stuff.

I've worked on a lot of weird stuff, big cap charging
supplies, pulse compressors, very high voltage or high
current, and tiny stuff with extremely low noise outputs.
But I don't have much experience with line frequency
magnetics beyond EMI filters. As you say there's
not much call for it now. But unfettered by
all the weak components the big iron can support
amazing overloads, so I think there's still a place
for it. At least for now. The cost of steel and
copper (and the transportation costs) for such heavy
beasts is certainly making them increasingly less
attractive.

Lately I've been working on equipment in the 10KW-60KW
output range switching at 75KHz range. The whole system
weighs much less than just the line frequency transformer
that would be required alone.

The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.


73


"Henry Kolesnik" wrote in
:

Hey Grump
A transformer is one of the simplest electrical machines and pretty well
understood in the classical design but when some of the parameters are
changed we don't have much experience or investigation and probably
wont. Hot swappable rectifier modules have made transformer based
rectifiers uneconomical kinda like carburetors and fuel injection. If
you have the time, check with some of the old time designers of
transformer rectifiers. Let me now what you find out. I had some notes
but those are long gone.
Hank

hey all:

A good trick for the lams is clear nail polish as you reassemble them.
Just a quick wipe, as it'll spread as you squeeze in the last few
lams
under a "Quick-Grip" clamp.

I could go to the nail shop get a peddicure and coat my lams at the
same time. A great idea if only I could handle the fumes.


Varnish is the best thing. Warm the varnish and the
transformer first before you dunk it. That will reduce
the viscosity and improve penetration. A little thinner
in the pot may help too.

I lucky I can stand the effects of epoxy but no way varnish. For nail
polish or varnish I gots to gits me a up or down draft venilator
exhastt system.

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

Thanks I retorqued them and that reduced the noise by 6db. Now I have
a less effecient buzzer

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.

Good idea I seen many a transformer that had fiber spacers over the
whole length of the bolt plus fiber washers..


put the
transformer into the box, and fill the box up with enough sand that
you
have 1-2 inches all around the transformer, and that might muffle the
buzz. You'll need to worry about heat dissipation through that sand
which
will act like an insulator, but if you are on the air only a couple
of
hours per day,

I likes this one, but I gots alot of kittie litter that comes from
some place in Arkansas, it is mostly quartz and some other trace
minerals.

The only big iron guys I know are now retired or dead.
And the companies I've dealt with that make that stuff
tend to have very little engineering staff, not much new
going on, (other than some efficiency improvements from
amorphous cores) they just crank out the product in cook
book fashion. I think nuances of it may soon be a lost.

Yes lams are going the way of the dinosuars. Maybe that's why they
cost so much looky the price of a good audio output transformer for a
tube audio amplifier and they go up to at least 20Khz.

Your other option is to figure out some clamping arrangement so that
the
laminations are held close and tight.

Yes I think I will put together a vise of sorts. Custom made to fit
the transformer.

73 and thanks for all the good information.

n8zu

On Tue, 28 Oct 2008 00:52:28 +0100 (CET), Grumpy The Mule
wrote:

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?


It's not just the laminations that make noise. The windings can
vibrate if they're not locked in place with transformer varnish or
epoxy. No amount of tightening the laminations will help if the
windings are free to vibrate. This is probably more likely in larger
higher power transformers (multiple kW) than in a filament or screen
supply transformer, but it can happen.

Also, depending on how much magnetic leakage your core has you can
couple to the steel walls of the cabinetry the transformer is housed
in if you don't maintain adequate spacing from the walls, in which
case the steel wall and the transformer can vibrate and make noise
even though no parts on the transformer are loose.

That's a good point. The filthy leakge inductance will be
spraying its flux all about. But there are things we can
do a to contain it.

A belly band around the winding (but not though the core) helps.
End bells (covers) bolted down over the windows work too.

There may also be fringing flux spewing out of the unavoidable
gaps if it's a butt stack lamination core. Interleaving the
laminations will help.

I've done all of that on a design with the transformer mounted
directly beneath the neck of the CRT in a video terminal.
A requirment of the project manager because he feared
SMPS noise and demanded a linear power supply. Of course
everything had to be jammed into the smallest possible
enclosure and a mu metal shield was deemed too expensive :P





Jim Higgins wrote in
:

It's not just the laminations that make noise. The windings can
vibrate if they're not locked in place with transformer varnish or
epoxy. No amount of tightening the laminations will help if the
windings are free to vibrate. This is probably more likely in larger
higher power transformers (multiple kW) than in a filament or screen
supply transformer, but it can happen.

Also, depending on how much magnetic leakage your core has you can
couple to the steel walls of the cabinetry the transformer is housed
in if you don't maintain adequate spacing from the walls, in which
case the steel wall and the transformer can vibrate and make noise
even though no parts on the transformer are loose.