I have some tube amp power transformers made locally (before the
factory burned down) and also some rather nice Tamradio rectangular
cans (used to be Jap 100v primary power trannys until I gutted them).
Problem is that the former dont fit in the latter - they miss out by
about a millimetre. Thinking back to the days when I messed around with
car engines, I wonder what the electrical implications of attacking the
side of the lam stack with a cylendar head grinder would be. The
Transformers are oversized electrically already (at least 50% over the
required power). Any gottchas ?.
M

" wrote:

I have some tube amp power transformers made locally (before the
factory burned down) and also some rather nice Tamradio rectangular
cans (used to be Jap 100v primary power trannys until I gutted them).
Problem is that the former dont fit in the latter - they miss out by
about a millimetre. Thinking back to the days when I messed around with
car engines, I wonder what the electrical implications of attacking the
side of the lam stack with a cylendar head grinder would be. The
Transformers are oversized electrically already (at least 50% over the
required power). Any gottchas ?.

It probably OK to clean them up by taking a mm off all around,
but just don't use heat, and don't let them get soaked with grinding
liquids, although if oil based it isn't so bad.
But you have to clean up ground metal and dry the trannys....

Patrick Turner..


M

For the SET amps I build, I had sanded the lams smooth and painted with
epoxy paint - gloss black. Someone who used to own a transformer company
told me it was bad, so I called Hammond (I use the 1627SE's). He said there
was no problem at all with smoothing out the laminations. The caveats added
by Patrick Turner are apt.
Dave

--
wrote in message
oups.com...
I have some tube amp power transformers made locally (before the
factory burned down) and also some rather nice Tamradio rectangular
cans (used to be Jap 100v primary power trannys until I gutted them).
Problem is that the former dont fit in the latter - they miss out by
about a millimetre. Thinking back to the days when I messed around with
car engines, I wonder what the electrical implications of attacking the
side of the lam stack with a cylendar head grinder would be. The
Transformers are oversized electrically already (at least 50% over the
required power). Any gottchas ?.
M

300B wrote:

For the SET amps I build, I had sanded the lams smooth and painted with
epoxy paint - gloss black. Someone who used to own a transformer company
told me it was bad, so I called Hammond (I use the 1627SE's). He said there
was no problem at all with smoothing out the laminations. The caveats added
by Patrick Turner are apt.
Dave

I have heard of ppl restamping the cut out size for the window
to make it bigger on standard wasteless patterns.
The shearing stresses cause magnetic problems, as would bending laminations.
So bending an hammering or shearing are not good.

But cold grinding is probably quite OK.

When they make C-cores the wind up a spiral of grain oriented steel strip
and bond it together with epoxy resin and cure with mild heat, which does not
affect the magnetic properties.
Then they saw through the 0 shaped core and grind and polish the cut ends so
making
two C from the 0 which can be clamped together to make very small size of gap
in the core, so a C core has an irom µ of maybe 1/3 of the µ of a continuous
uncut core,
like that used in a toroidal tranny.
So its the fine gap that alters the magnetics, not grinding, which actually
improves the
join, so i can't see why grinding 1% off a bit of the outside off a tranny will
change much at all.

As regards heat, my experience with grain oriented silicon steel is that it
doesn't do it much harm.

Last year I found I had accumulated a wheelbarrow full of old trannies with odd
windings, or open windings,
some audio, some mains, and the job of stripping them down is hard yakka.
So I just piled them into an open fire for 1/2 an hour until they turned cherry
red, and pulled them
out and let them cool over night.
The next day I used an small angle grinder to cut the bolts, and cut the copper
wire, and the
laminations all just fell apart, no longer held tight by varnish and bobbin,
also evaporated in the process.

A few Kgs of the laminations I gained this way were known to be GOSS
with a maximum µ = 5,000. After cooking like I did it didn't change
to any great extent, ie, the magnetic properties were the same, and µ remained
the same,
so I could reuse the material for chokes.
This stands to reason because the GOSS I buy has been heated in a furnace
for quite some time before it is sold to me.
GOSS hase been annealed.

When grinding a tranny to fit into a can, one should do the sides one needs to,
but after some thought, I wonder, will it work to give a neat and quiet tranny?

BUT, and there is always a but, what is the can material?
If it is mild steel, there should be a gap between the can and the core, because
if not
the can may buzz with the external magnetic field put out from the core
due to mains flux leakage.

In some amps I have built the steel covers over mains trannies have hummed more
as clearance reduces,
and I have had to resort to drilling holes in the covers, and gluing fibre board
to the inside of the steel
cover, or making a steel can myself, and potting the tranny by pouring in molten
roof pitch
heated to about 180C.
This last method was able to silence a particularly noisy C-core tranny,
not unusual because it is rated for 1.1kW, and despite the Bmax being only 0.85
Tesla.
I have also used handmade pots to encase chokes used for choke input PS.


So rather than alter the tranny to fit the can, how about making new cans?

I do this by cutting a block of wood *accurrately* and with *square angles*
to the wanted inside size of the can, and bend some mild steel sheet around the
block
with clamps, hammer, and blocks of scrap wood to not dent the iron sheet.
Then I make a couple of internal fitting lids, and poprivet the lot together
I also allow for fixing bolts or angles etc.
I seal the inside with some silicone smeared around, and leave a hole say 2" dia
big enough to
pour in some pitch and have the wires come out, and its done.
Wires for pitched trannies have to be sleeved with fibreglass sleeving,
since pvc will melt when the hot pitch hits it.
There are other potting materials; polyurethane and epoxy is available.
But some of this stuff gives off heat when it hardens, and shrinks, so the right
stuff for potting
is expensive.

The simplest way to fit trannies is to use bellends.

Patrick Turner.







--
wrote in message
oups.com...
I have some tube amp power transformers made locally (before the
factory burned down) and also some rather nice Tamradio rectangular
cans (used to be Jap 100v primary power trannys until I gutted them).
Problem is that the former dont fit in the latter - they miss out by
about a millimetre. Thinking back to the days when I messed around with
car engines, I wonder what the electrical implications of attacking the
side of the lam stack with a cylendar head grinder would be. The
Transformers are oversized electrically already (at least 50% over the
required power). Any gottchas ?.
M