amperage and watts

[rtill]

Is it crucial that a transformer has a certain amount of amps to produce a certain amount of watts?

example.... a 5 amp transformer is needed to push out 100 watts, all I can find is a 2 amp transformer....will I get 100 watts?

[Nigel Goodwin]

Thing of it this way - if it takes you a gallon of beer to get drunk, and you can only afford to buy two pints of beer, will that get you just as drunk!.

[richie00boy]

Or more theoretically, watts is amps multiplied by volts, so if the volts are the same and you only can do 2 amps instead of 5 amps, you are not going to get the same watts.

[wg_ski]

Originally posted by rtill
Is it crucial that a transformer has a certain amount of amps to produce a certain amount of watts?

example.... a 5 amp transformer is needed to push out 100 watts, all I can find is a 2 amp transformer....will I get 100 watts?

If the supply voltage doesn't drop too much, yes. What you end up doing is running off a higher unloaded voltage so it droops down to what it would have off the higher-amp transformer. The catch is you can't play it as loud for as long before it runs hot.

This seems to be the basis for all these "smaller lighter cheaper" amplifiers out there, so you won't be doing anything unusual.

[rtill]

ok, so here's my next question.....
let's say the circuit needs 90 volts at 5 amps for 100 watts.

my choices for transformers are.....

a 60 Volt c.t. at 5 amps - after rectified I get 84 Volts
or
a 64 Volt c.t. at 2 amps - after rectified I get 90 Volts

Which would be a better choice?
Would the 6 Volts make a huge difference so I don't get 100 watts? or do I risk damaging the circuit by overheating with not enough amps.....

[wg_ski]

Originally posted by rtill
a 60 Volt c.t. at 5 amps - after rectified I get 84 Volts
or
a 64 Volt c.t. at 2 amps - after rectified I get 90 Volts

Which would be a better choice?

You won't get 100 watts out of either one. But the 60V/5A one will probably be closer. Best guess without measurements puts the bigger one at 68 volts rectified under load and the smaller one at 63 volts.

You don't risk damaging the *circuit* with a transformer with too low a current - the transformer itself will run hot. If you wanted to bump up the unloaded voltage to make sure you get 100 watts, you need a 70-80 vct, perhaps 90 vct if it was really undersized. THAT may damage the circuit if it isn't meant to take it.

[myhrrhleine]

Hello,

secondary volts x amps=watts.
The bigger transformer would be better.

[rtill]

http://www.elecfree.com/circuit/powe...3055-with-pcb/

This is the circuit I'm looking at building.......

[CBS240]

Originally posted by rtill
....or do I risk damaging the circuit by overheating with not enough amps.....

Maybe not damage the circuit, but by counting on the higher voltage transformer to droop in order to get the amps needed may cause the transformer core to saturate, that's why it gets hot. It is best to have a transformer that matches the impedance of the circuit, i.e. correct voltage and current. Use a larger transformer if needed. You can parallel transformers as long as the are exactly alike, observing polarity. Besides, you would want to have as little possible ripple on the filter caps anyway, eh? Sure not going to get this by an overdriven power transformer. core....

[jaycee]

That circuit is dreadful - theres no reason to use a single ended design these days, especially if your transformer has a centre tap.

With the 60VCT transformer, i'd say build Bora's "Techno" amplifier circuit. It wont quite be 100W but it will sound good.