US powered amps-does it suck?

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bender
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Re: US powered amps-does it suck?

Post by bender »

tubeswell wrote:Rewinding is a waste of money. The amount of iron in PTs made for US voltages is typically about 10-20% less than iron in PTs made for 230 mains voltage that are supposed to deliver the same secondary VA (purely because of production cost reasons). Rewinding is just putting more coils into the same size bobbin in the same iron. This means the iron has to induce more magnetising current than it was designed for, and the result is the PT will run hotter and tend to overheat.

Compare the two sine wave functions in the attached graph. The area under each function curve represents the total power that has to be induced through the core, and the 50Hz-230VAC sine wave has greater area. This means, all other things - like the secondary voltages etc- being equal, a 230V 50Hz PT needs to be bigger to stay cool.

Better to swap the US PT out for a 230 mains PT (if it doesn't already have a mains voltage selector).
Oh bummer. I went with Clarry's advice on my Bandmaster. :(

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Re: US powered amps-does it suck?

Post by tubeswell »

bender wrote:
tubeswell wrote:Rewinding is a waste of money. The amount of iron in PTs made for US voltages is typically about 10-20% less than iron in PTs made for 230 mains voltage that are supposed to deliver the same secondary VA (purely because of production cost reasons). Rewinding is just putting more coils into the same size bobbin in the same iron. This means the iron has to induce more magnetising current than it was designed for, and the result is the PT will run hotter and tend to overheat.

Compare the two sine wave functions in the attached graph. The area under each function curve represents the total power that has to be induced through the core, and the 50Hz-230VAC sine wave has greater area. This means, all other things - like the secondary voltages etc- being equal, a 230V 50Hz PT needs to be bigger to stay cool.

Better to swap the US PT out for a 230 mains PT (if it doesn't already have a mains voltage selector).
Oh bummer. I went with Clarry's advice on my Bandmaster. :(
He probably mean't winding a new PT. Rewinding an existing transformer is usually a last option because of the messiness and time involved. (I know Clarry reasonably well and have dealt with him for 10 years. I don't believe he would recommend that option in the 1st instance.)
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Re: US powered amps-does it suck?

Post by bender »

tubeswell wrote:
bender wrote:
tubeswell wrote:Rewinding is a waste of money. The amount of iron in PTs made for US voltages is typically about 10-20% less than iron in PTs made for 230 mains voltage that are supposed to deliver the same secondary VA (purely because of production cost reasons). Rewinding is just putting more coils into the same size bobbin in the same iron. This means the iron has to induce more magnetising current than it was designed for, and the result is the PT will run hotter and tend to overheat.

Compare the two sine wave functions in the attached graph. The area under each function curve represents the total power that has to be induced through the core, and the 50Hz-230VAC sine wave has greater area. This means, all other things - like the secondary voltages etc- being equal, a 230V 50Hz PT needs to be bigger to stay cool.

Better to swap the US PT out for a 230 mains PT (if it doesn't already have a mains voltage selector).
Oh bummer. I went with Clarry's advice on my Bandmaster. :(
He probably mean't winding a new PT. Rewinding an existing transformer is usually a last option because of the messiness and time involved. (I know Clarry reasonably well and have dealt with him for 10 years. I don't believe he would recommend that option in the 1st instance.)
Nope. It was specifically his advice for changing my 1967 Bandmaster to NZ power.

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Re: US powered amps-does it suck?

Post by tubeswell »

Well I'll be dayyumed.
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Re: US powered amps-does it suck?

Post by sizzlingbadger »

Maybe those transformers are worth the effort, some old amps have real chunky iron in them.
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Re: US powered amps-does it suck?

Post by bender »

sizzlingbadger wrote:Maybe those transformers are worth the effort, some old amps have real chunky iron in them.

Actually- that does ring a bell... I think I remember him saying something about it being big enough to handle it.

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