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

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.

On Sat, 25 Oct 2008, raypsi wrote:

Date: Sat, 25 Oct 2008 10:25:23 -0700 (PDT)
From: raypsi
Newsgroups: rec.radio.amateur.homebrew
Subject: I built a 7.5VAC 21Amp transformer now it has lots of buzz

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


This might be a little "far-out" but, besides just buying more epoxy and
just doing it right, maybe you could find a can or metal box, 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, it should not get dangerously hot (however, many of the old
hermetically sealed transformers were burried in a waxy-tar that was
quite hard at room temperature).

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

Re-winding transformers is fun, but next time you want some off-beat
voltage, maybe scrounge up higher voltages (eg. car battery chargers)
and use either a variac or power resistor (with sufficient heat
dissipation) to bring the voltage down to where you want it and save
yourself the headaches and earaches. Or, don't take the laminations apart
but feed the wire (stranded) through the holes that are left.

Or, other kludge-cheapskate approaches.

Good luck.

It's not so far out of a suggestion. One of my Zenith console
radios has some remote control solenoid mounted inside a metal
box that's lined with rubber.

The sand is a pretty good thermal conductor (compared to air),
better than epoxy. In fact they fill the cheaper type of epoxy
potting material with coarse quartzite or powdered limestone
to improve its the thermal conductivity. It's the air trapped
between the grains of sand that provide some thermal insulation.
Mixing sand with epoxy or oil fills the interstaces which would
otherwise be filled with air.

Some one mentioned coating the laminations with nail polish as you
stack them up to glue them together. Either that or little varnish
would most likely have prevented any buzzing laminations.

Not taking the laminations off is a good suggestion too if it's
possible. For instance microwave oven transformers just chisel
off the secondary and wind a new one. Though for smaller
transformers that often isn't possible.




Stray Dog wrote in
.org:


This might be a little "far-out" but, besides just buying more epoxy
and just doing it right, maybe you could find a can or metal box, 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, it should not get dangerously hot
(however, many of the old hermetically sealed transformers were
burried in a waxy-tar that was quite hard at room temperature).

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

Re-winding transformers is fun, but next time you want some off-beat
voltage, maybe scrounge up higher voltages (eg. car battery chargers)
and use either a variac or power resistor (with sufficient heat
dissipation) to bring the voltage down to where you want it and save
yourself the headaches and earaches. Or, don't take the laminations
apart but feed the wire (stranded) through the holes that are left.

Or, other kludge-cheapskate approaches.

Good luck.

On Oct 27, 11:29*pm, Stray Dog wrote:
On Sat, 25 Oct 2008, raypsi wrote:
Date: Sat, 25 Oct 2008 10:25:23 -0700 (PDT)
From: raypsi
Newsgroups: rec.radio.amateur.homebrew
Subject: I built a 7.5VAC 21Amp transformer now it has lots of buzz

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

This might be a little "far-out" but, besides just buying more epoxy and
just doing it right, maybe you could find a can or metal box, 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, it should not get dangerously hot (however, many of the old
hermetically sealed transformers were burried in a waxy-tar that was
quite hard at room temperature).

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

Re-winding transformers is fun, but next time you want some off-beat
voltage, maybe scrounge up higher voltages (eg. car battery chargers)
and use either a variac or power resistor (with sufficient heat
dissipation) to bring the voltage down to where you want it and save
yourself the headaches and earaches. Or, don't take the laminations apart
but feed the wire (stranded) through the holes that are left.

Or, other kludge-cheapskate approaches.

Good luck.- Hide quoted text -

- Show quoted text -

I have always dunked them in varnish but only got some success with
this by
drawing a vaccum then applying pressure. I used an old compressor
from
a refrigarator to do this. The tank was made from from pipe and
fittings. The best
results I got was winding the core on a block of wood cut the same
size as
the core wrapping the wood with cardboard then windng the coil then
pushed
then put the core together. I was 18 at the time and a very talented
man
named Olin Griggs helped me with this project and let me use his
shop.
Olin was a retired engineer that had worked for GE at their
Bloomington plant.
Since then the onl transformers I have wound that havent bussed to
much
was by modifying a ready built transformer. USually this meant one
that I
on which I could keep the primary winding intact. Lately I have gotten
interested
in SMPSs for doing this sort of thing. It is very easy to see why
industry has
has made the move to them.

Jimmie