Va rating reloaded

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Dear all,

I recently got a hold of a toroid trafo with unknown va rating. I had started a similar thread on this topic some time back but I have brought it again just to recap.
The trafo specs are as follows:

220v ac input
44-0-44 output
Weight 3.8 kg
Outer diameter 12.5 cm
Height 8.4 cm
Twisted pair of 1mm thick wires per 44 volt winding.

With these specs can you deduce an estimate of the va rating?
 
t
hanks people.
Andrew T , thats a good estimation.
Tony i did'nt get the primary resistance but my rough estimation should be 2.5ohms to 3.5 ohms. i will give the correct reading when i get home.

now that Andrew T has given his rough estimate, i have plans on using it on Apex audio's HV23 amplifier rated 350w 4ohms, 200w 8 ohms. is it worth the try?
 
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..... i have plans on using it on Apex audio's HV23 amplifier rated 350w 4ohms, 200w 8 ohms. is it worth the try?
You probably realize that the HV23 is specified with 75V power rails but with your transformer, they will be considerably less at ~65V. The power may then be around 180W/8R and 300W/4R, allowing for voltage sag with such a small transformer. There are cheaper circuits suitable for this lower power.

There's not much point building such a large amplifier for pro. use when you plan to skimp on the power supply. It just makes no sense.
 
primary resistance reloaded: the actual resistance measured is 2.7 ohms.

thanks Ian for your advice. i have taken into consideration that the power will be less. but i want still to make it regardless of the power reduction.

want to ask further if there is going to be other important values like the bias voltage will change if i make the HV23.
 
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.... i have taken into consideration that the power will be less. but i want still to make it regardless of the power reduction......the bias voltage will change if i make the HV23.
It's good to have considered the lower power but the issue is that you won't be able to properly drive low impedances like 4R even. The amplifier will need a good, well adjusted protection system specifically for low impedance loads or the transformer will overheat unless it is rated to supply the full current demand appropriate to the rail voltages. This also means knowing how to set it up with current limiting for your transformer, not just protecting the output stage Apexaudio designed it for.

Bias requirements are current, usually measured as a voltage across the source resistors. It is not a critical value in a Mosfet amplifier and doesn't need to change from ~ 50-100mA per each output pair, regardless of power. It does have to be well controlled though, to compensate for varying loads and temperature to prevent thermal runaway.

I'm not saying you can't do what you want, nor that your plan won't work - almost any combination will work, even without limiters for home use, but it will be too bad when you find out the fundamental problems of a weak design when you can ill-afford it, in a hardworking PA amplifier.

I suggest you ask the designer of the amplifier what he recommends in your situation - assuming your transformer is only in the 400VA ball-park and you do want to use it as a PA, disco amp etc.
 
Thanks Sirs for your advice. Now another thing I wanted to ask. I have an 8channel powered mixer. I occasionally use it and the last time I used, it gave a humming sound through the speakers. I suspected the resister that links the groumd to the earth wire was defective but even after replacin it the hum remained. I changed the. PSU filter caps but still the same. Is there any other culprit that I should look for durin further troubleshooting?
 
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A correct schematic and clear pics of the board, wiring and chassis would be needed to make suggestions for an unknown device. Even though the problem is very common, there are so many possibilities that it would be guesswork otherwise. Is it a stereo mixer? Is it working normally apart from the hum?

Perhaps you could start by measuring some basics, like the (~20mV) DC voltage across the amplifier output terminals when neither inputs or speakers are connected to it. Unless this is a Mosfet design, you could carefully (don't slip!) measure the base-emitter DC voltage (~0.6V) of all the transistors to get an indication they are functional. Post anything you think is wrong.

It would be better to start a new thread for a this new topic.
 
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i did a few checks including what Ian told me. they are as follows:
output NPN transistors: Vbe= 0.292v
output PNP transistors: Vbe= 0.105v
output terminals: Left channel: 24.76mv
Right Channel: 20.35mv
i also tested for defects in all transistors of both amplifiers, non of them were defective.
 
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