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Can anyone tell me how to measure t...

9/9/2000 6:44 PM
anonymous Can anyone tell me how to measure t...
Can anyone tell me how to measure the impedance ratio of a transformer?  
I've got an old stereo amp that runs 6v6s push-pull per channel, but it's not indicated anywhere what the load should be.  
I should be able to apply a specific low voltage AC signal to the secondary and measure the resulting voltage on the primary. I've got a signal injector probe that generates 700mv. Will that work?  
I don't know the formula for determining the impedance ratio once I've got the voltages.  
Am I even in the ballpark with this process?  
9/9/2000 6:47 PM
Don Symes
THere's some transformer evaluation information on
9/9/2000 8:40 PM
Re:Figuring the OT primary
It might be able to generate 700mv into a 600ohm load but probably not the secondary of an OT.  
If you have an old filament tranny laying around you can use that.  
6.3v (or what ever it measures when you connect it across the secondary) will generate about +200vac on the primary so be carefull!!  
Take the applied "measured" secondary voltage (6.3vac) and divide it into the resultant "measured" primary voltage (200vac) and square that number.  
That new number times what ever the speaker load,  
is the primary Zed.  
6.3vac sec, 200vac primary.  
200vac/6.3vac = 31.7  
31.7 x 31.7 = 1,008.  
1008 x 8 ohm speaker = 8064 ohms on the primary when using an 8 ohm speaker on the secondary.  
9/10/2000 7:06 PM
Thanks Bruce. This is exactly the info i was looking for. Actually I don't have a filament transformer, but I do have a variaC. i didn't think of that till you mentioned this. Thanks. Plus this way I can try to keep the applied voltage to 1 or 2 volts. I know this may make the measurement a little less reliable (lower "resolution") but should be a bit safer, and since I've got a couple DVMs I can monitor the input voltage.  
thanks again for the info.
9/11/2000 2:00 AM

You can use it backwards with a little higher voltage on the primary then and step it down to the secondary.  
Same voltage ratio up or down as far as I know.  

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