I am building an OTL amplifier, and want to use an industrial control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I hooked
120vac to the 120v side, there was an annoying hum. It doesn't look
used- I got it on ebay a while ago. Can I expect the hum to go away
after a while of usage, or can it be expected to persist. Thanks,

gojamo wrote:

I am building an OTL amplifier, and want to use an industrial control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I hooked
120vac to the 120v side, there was an annoying hum. It doesn't look
used- I got it on ebay a while ago. Can I expect the hum to go away
after a while of usage, or can it be expected to persist. Thanks,

Try tightening the screws or frame holding the lams, or
maybe the core is a little loose. Use a wedge shaped
toothpick slipped between the inside of the core and the
coil.

robert casey wrote:

gojamo wrote:

I am building an OTL amplifier, and want to use an industrial control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I hooked
120vac to the 120v side, there was an annoying hum. It doesn't look
used- I got it on ebay a while ago. Can I expect the hum to go away
after a while of usage, or can it be expected to persist. Thanks,

Try tightening the screws or frame holding the lams, or
maybe the core is a little loose. Use a wedge shaped
toothpick slipped between the inside of the core and the
coil.

Mechanical tightening of screws, and wedging thin wide
pieces of plastic between the windings and core may not cure the hum.

It will only grow worse.

Perhaps vacuum impregnation with varnish and baking at the right temp
for 4 hrrs might help, but might not, if there is already a sealed
potion of windings into which the varnish cannot be forced
with air pressure after vacuuming.

I get a stream of ppl bringing me crap items purchased on Ebay with hum
problems
in the PT.
Its often why folks are selling; they get rid of problems for a $.

Patrick Turner.

"Patrick Turner"

I get a stream of ppl bringing me crap items purchased on Ebay with hum
problems in the PT.
Its often why folks are selling; they get rid of problems for a $.



** Louie the fly,

Louie the Fly -

straight from rubbish tip to YOU.






............. Phil

"Patrick Turner" wrote in message
...


robert casey wrote:

gojamo wrote:

I am building an OTL amplifier, and want to use an industrial control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I
hooked
120vac to the 120v side, there was an annoying hum. It doesn't look
used- I got it on ebay a while ago. Can I expect the hum to go away
after a while of usage, or can it be expected to persist. Thanks,

Try tightening the screws or frame holding the lams, or
maybe the core is a little loose. Use a wedge shaped
toothpick slipped between the inside of the core and the
coil.

Mechanical tightening of screws, and wedging thin wide
pieces of plastic between the windings and core may not cure the hum.

It will only grow worse.

Perhaps vacuum impregnation with varnish and baking at the right temp
for 4 hrrs might help, but might not, if there is already a sealed
potion of windings into which the varnish cannot be forced
with air pressure after vacuuming.

I get a stream of ppl bringing me crap items purchased on Ebay with hum
problems
in the PT.
Its often why folks are selling; they get rid of problems for a $.

Patrick Turner.

That is a great caveat for power xfrs. Did you ever have problems with ebay
opts?
Cordially,
west

I have a transformer well until I potted it, I could have used it for a
60hz siren it was so loud. It would have made a great bed vibrator too.


I potted mine in a 50 50 mix of bondo poyester resin and kitty litter.
1). I poured a layer of resin and kitty litter 1/4" on the bottom of a
34 oz coffee can.
2). After that hardened I dropped in the transformer. With a terminal
board attached to bring out the connections.
3). Then I layered the resin mix 4 more times to fill it up to the
terminal board. Each layer I let harden.

Now talk about a transformer.

"gojamo" wrote

I am building an OTL amplifier, and want to use an industrial
control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I
hooked
120vac to the 120v side, there was an annoying hum. It doesn't
look
used- I got it on ebay a while ago. Can I expect the hum to go
away
after a while of usage, or can it be expected to persist. Thanks,

It can only get worse.

You don't mention what you had connected to the secondary. How much
it hums will depend on the load, so you should check with the
intended load.

If it is rattling on its mountings, then tightening will quieten it,
but if is mounted to a poorly designed chassis it could act as a
soundboard. Mounting on soft rubber may then be better, or
stiffening the chassis, or both.

cheers, Ian

"robert casey" wrote in message
ink.net...
gojamo wrote:

I am building an OTL amplifier, and want to use an industrial
control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I
hooked
120vac to the 120v side, there was an annoying hum. It doesn't
look
used- I got it on ebay a while ago. Can I expect the hum to go
away
after a while of usage, or can it be expected to persist. Thanks,

Try tightening the screws or frame holding the lams, or
maybe the core is a little loose. Use a wedge shaped
toothpick slipped between the inside of the core and the
coil.

Many years ago I cured one by simmering it in shellac varnish for an
hour (outside!)
Cheers,
Roger

west wrote:

"Patrick Turner" wrote in message
...


robert casey wrote:

gojamo wrote:

I am building an OTL amplifier, and want to use an industrial control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I
hooked
120vac to the 120v side, there was an annoying hum. It doesn't look
used- I got it on ebay a while ago. Can I expect the hum to go away
after a while of usage, or can it be expected to persist. Thanks,

Try tightening the screws or frame holding the lams, or
maybe the core is a little loose. Use a wedge shaped
toothpick slipped between the inside of the core and the
coil.

Mechanical tightening of screws, and wedging thin wide
pieces of plastic between the windings and core may not cure the hum.

It will only grow worse.

Perhaps vacuum impregnation with varnish and baking at the right temp
for 4 hrrs might help, but might not, if there is already a sealed
potion of windings into which the varnish cannot be forced
with air pressure after vacuuming.

I get a stream of ppl bringing me crap items purchased on Ebay with hum
problems
in the PT.
Its often why folks are selling; they get rid of problems for a $.

Patrick Turner.

That is a great caveat for power xfrs. Did you ever have problems with ebay
opts?

Not me personally, because I have yet to trade via Ebay, ie, buy anything.
But I have see 3 amps/recievers with dud OPTs.

One guy just parked the item on which he'd wasted $150,
then went looking for another, and this time he was lucky, and it worked.

Patrick Turner.


Cordially,
west

ray13 wrote:

I have a transformer well until I potted it, I could have used it for a
60hz siren it was so loud. It would have made a great bed vibrator too.

I potted mine in a 50 50 mix of bondo poyester resin and kitty litter.
1). I poured a layer of resin and kitty litter 1/4" on the bottom of a
34 oz coffee can.
2). After that hardened I dropped in the transformer. With a terminal
board attached to bring out the connections.
3). Then I layered the resin mix 4 more times to fill it up to the
terminal board. Each layer I let harden.

Now talk about a transformer.

The trouble with loose wires is now hidden inside, and
maybe it gets a shorted turn some day...

One really needs to minimize noise before potting.
S vacuum varnishing is worth trying with an old tranny.
If it is waxed, then soaking in molten wax is a good idea, since varnish is
incompatible
with wax.
The potting can be done using clean dry sand or as you have used, kitty
litter, and wax.
The tranny should be secured well inside the pot with wax, and if possible
the
can should be siliconed shut so if the wax ever melts it cannot leak out.
Wax melts at about 50C.
While the tranny is below 35C, the wax stops wires buzzing together
fairly well, but varnish is better.
After varnishing, it can be potted in wax though because the varnish when
baked
with no wax present becomes impervious to molten wax.
The wax allows easier rewinding in future, after retrieving the cores.

The easiest way to get varnished cores out of old iron cored
items with stuffed windings is to place then in a small log fire for
20 minutes until the core just turns dull red.
Then allow them to cool down over night.
The wires and bolts are easily cut with a small angle grinder, and the
wound item
fall apart.
The heat does not affect the already annealed laminations, and while bolted
together
the lams don't oxidise.
But all the varnish is vaporized, just leaving a dusty layer of carbon.

I did a barrow load of old buggered trannies last year, and I use the cores
for chokes
and sometimes radio OPTs, etc.

Patrick Turner.

Engineer wrote:

"robert casey" wrote in message
ink.net...
gojamo wrote:

I am building an OTL amplifier, and want to use an industrial
control
transformer type Hevi-Duty .850kw 120v:208v that I have. When I
hooked
120vac to the 120v side, there was an annoying hum. It doesn't
look
used- I got it on ebay a while ago. Can I expect the hum to go
away
after a while of usage, or can it be expected to persist. Thanks,

Try tightening the screws or frame holding the lams, or
maybe the core is a little loose. Use a wedge shaped
toothpick slipped between the inside of the core and the
coil.

Many years ago I cured one by simmering it in shellac varnish for an
hour (outside!)
Cheers,
Roger

yes, shellac has also often been used as a soak in type of
impregnant.

Very neccessary to do any of the process outside,
and use only electically heated stoving with good temp control.
The fumes will kill elephants, and then there is a fire risk,
and the neighbours will complain about the pong.....
Heating the transfomer to about 70C and then plunging it
into a vat of shellac will help suck in the shellac as the item cools.

Patrick Turner.

"Patrick Turner" wrote in message
...


Engineer wrote:
Many years ago I cured one by simmering it in shellac varnish for
an
hour (outside!)
Cheers,
Roger

yes, shellac has also often been used as a soak in type of
impregnant.

Very neccessary to do any of the process outside,
and use only electically heated stoving with good temp control.
The fumes will kill elephants, and then there is a fire risk,
and the neighbours will complain about the pong.....
Heating the transfomer to about 70C and then plunging it
into a vat of shellac will help suck in the shellac as the item
cools.

Patrick Turner.

Oh, dear... I used a primus stove outside (kerosene fired), an
asbestos mat with transformer and shellac in a saucepan. Kept the
heat low, nothing blew up!
Disclaimer: DON'T TRY THIS - I might have just got lucky!
Cheers,
Roger