Hi,
I need to convert an English ss amp "monogram reference 3100 class A+" back to 220v. I suppose it was factory rewired in US for using 110v mains supply.
In the interior of the amp, I found that the wire a, b and c from the power suupply sockets were connected to the power transformer as follows:-
wire a to wire w and x
wire b to wire y and z
wire c to wire c' (earth)
I believe that the transformer has a dual primary windings (it was designed to take 110 to 240v.
My questions are:
1/ could the conversion be done by shorting the wires x and y, or wires x and z?
2/ what would be the consequence of mis-connection?
3/ has anyone heard about this amp before?
Thank you in advance for your kind help.
Best wishes,
Russell SIT
I need to convert an English ss amp "monogram reference 3100 class A+" back to 220v. I suppose it was factory rewired in US for using 110v mains supply.
In the interior of the amp, I found that the wire a, b and c from the power suupply sockets were connected to the power transformer as follows:-
wire a to wire w and x
wire b to wire y and z
wire c to wire c' (earth)
I believe that the transformer has a dual primary windings (it was designed to take 110 to 240v.
My questions are:
1/ could the conversion be done by shorting the wires x and y, or wires x and z?
2/ what would be the consequence of mis-connection?
3/ has anyone heard about this amp before?
Thank you in advance for your kind help.
Best wishes,
Russell SIT
Transformer wiring
IF it does have dual primary windings, (they should be in parallel for 110V), they should be wired in series & in phase for 220V.
BE CAREFUL....
IF it does have dual primary windings, (they should be in parallel for 110V), they should be wired in series & in phase for 220V.
BE CAREFUL....
How to know they are in phase?
Thank you to your prompt reply.
How could I be certain that the 2 primary windings connected are in phase? What would happen if they are connected out of phase, e.g. blow the fuse, transformer or the whole amp, or just no output from the big iron?
Best wishes,
Russell SIT
Thank you to your prompt reply.
How could I be certain that the 2 primary windings connected are in phase? What would happen if they are connected out of phase, e.g. blow the fuse, transformer or the whole amp, or just no output from the big iron?
Best wishes,
Russell SIT
phased out
Out of phase, you should get next to no output.
Probably best to disconnect the secondary from the amp circuitry before you start playing with this.
Pete McK
Out of phase, you should get next to no output.
Probably best to disconnect the secondary from the amp circuitry before you start playing with this.
Pete McK
They told me to use a fuse on the input too. If it is wrong the fuse will blow mighty fast avoiding a melt down Is this true that out of phase is possibly dangerous ?
See the first schematic (Type 7 primary) here:
http://www.plitron.com/pages/Products/Std/schemati.htm
If you wire them out of phase it won't blow the fuse, just give very little output, as Pete said. But always use a fuse.
http://www.plitron.com/pages/Products/Std/schemati.htm
If you wire them out of phase it won't blow the fuse, just give very little output, as Pete said. But always use a fuse.
I would try to connect:
wire a to wire w
wire x with wire y
wire b to wire z
providing that x-y is not the same winding (but rather w-y and x-z are the same). Before that, disconnect secondaries from the circuit and make sure the primary has a fuse..
wire a to wire w
wire x with wire y
wire b to wire z
providing that x-y is not the same winding (but rather w-y and x-z are the same). Before that, disconnect secondaries from the circuit and make sure the primary has a fuse..
If you can , make some measurements.
1. Disconect all the primary and secondary wires.
2. Check the Inductance and Rezistance in primary.
3. Try to discover two windings with same characteristics.
4. Conect in series and measure the inductance.
- If the inductance is double it is OK
- If the inductance is half it is not OK becouse is out of phase.
5. Inject in the new primary a small tension ( 24 v AC ) from a small transformer and check the voltage in secondary.
If everything is OK you can try to 240V for a very short time.
1. Disconect all the primary and secondary wires.
2. Check the Inductance and Rezistance in primary.
3. Try to discover two windings with same characteristics.
4. Conect in series and measure the inductance.
- If the inductance is double it is OK
- If the inductance is half it is not OK becouse is out of phase.
5. Inject in the new primary a small tension ( 24 v AC ) from a small transformer and check the voltage in secondary.
If everything is OK you can try to 240V for a very short time.
djdan,
If the two windings are serial conected in phase, inductance will be 4 times higher, because of the mutual inductance.
If the two windings are serial connected out of phase, inductance will be very low (theoretically zero), because, again, of the mutual inductance. This misconnection used with 240 vac supply can destroy the transformer in few seconds.
A good idea is to try the transformer with 24 vac instead of 240 vac, and to measure the voltage across secondary winding, wich must be 1/10th of the normal working voltage if all is correct. No voltage, or very low, denotes out of phase primary connection.
Regards, Pierre Lacombe.
If the two windings are serial conected in phase, inductance will be 4 times higher, because of the mutual inductance.
If the two windings are serial connected out of phase, inductance will be very low (theoretically zero), because, again, of the mutual inductance. This misconnection used with 240 vac supply can destroy the transformer in few seconds.
A good idea is to try the transformer with 24 vac instead of 240 vac, and to measure the voltage across secondary winding, wich must be 1/10th of the normal working voltage if all is correct. No voltage, or very low, denotes out of phase primary connection.
Regards, Pierre Lacombe.
Doh!! I could use a selection from my Variac collection to run lower voltage through it. This is kinda embarrassing.......
Also the obvious is if they are connected in phase in parallell today you need to connect them for series using one wire of each connection point a and b and then you know it is in phase. Peter suggested exactly that.
/UrSv
/UrSv
transformer
After you connected the primaries in series connect them via a 100 W light bulb in series to the to the mains.
If it lights up at almost full brightness you should change your wiring, if its dim everything's alright.
Arne
After you connected the primaries in series connect them via a 100 W light bulb in series to the to the mains.
If it lights up at almost full brightness you should change your wiring, if its dim everything's alright.
Arne
Thank you for the advices and suggestions
I would like to thank all of you who have offered advices on the voltage conversion.
I have made it, by try-and-error. The amp is now singing nicely, albeit a little hum.
Just one thing I want to point out: the fuse would blow, and in fact blow badly, if the connection is out of phase.
Thank you again for the advices and suggestions.
Best wishes,
Russell SIT
I would like to thank all of you who have offered advices on the voltage conversion.
I have made it, by try-and-error. The amp is now singing nicely, albeit a little hum.
Just one thing I want to point out: the fuse would blow, and in fact blow badly, if the connection is out of phase.
Thank you again for the advices and suggestions.
Best wishes,
Russell SIT
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