How to spec an unmarked power TX?
- Thread starter Ethan
- Start date
Help Support GroupDIY Audio Forum:
Mark Burnley
Well-known member
Ethan,
The first thing to do is work out the individual windings using a DMM set to the "Ohms" range. Take each wire in turn and test for continuity between the other wires. When you find continuity, write down the connections (or tape the wires together if flying leads). If you find three wires all showing continuity, then you have a CT or "centre tap" winding. The centre wire will be the wire that is disconnected when the other two wires show a maximum resistance reading.
If you find 4 or more wires showing continuity, it's probably a multi-tap mains input primary.
Once you've done this, you can see how many windings you've got, and what connections are which. Next, you need to find the voltage ratios. I find the easiest way to do this is using a small 6V transformer (the type used in cheap cassette recorders or portable radios). The theory here is that 6V is a low-enough voltage to not cause any damage to the windings.
Connect your 6V ac from the small transformer to a winding of your unknown transformer. Then carefully measure the ac voltages at the other windings. Switch off the power before changing the meter probes- say for example the winding you've connected the 6V to is actually a 6V winding, and then you touch another winding which is rated at 240V, then 240V will appear at that windings terminals!
You'll now have a voltage reading next to each winding. From this you can work out which winding is which. The mains winding is usually instantly recognisable- especially if it's a non-tube type transformer. With a lower-voltage type transformer, you'll see a massive ratio between one winding and all the others- this is the mains primary.
I hope this helps- I've managed to salvage many surplus "unknown" transformers using this method. Let me know when you've worked out which windings are which, and we'll see if we can work out the rest of the ratings.
Of course, the easiest method is if someone has a data sheet already for this model :wink:
Mark
The first thing to do is work out the individual windings using a DMM set to the "Ohms" range. Take each wire in turn and test for continuity between the other wires. When you find continuity, write down the connections (or tape the wires together if flying leads). If you find three wires all showing continuity, then you have a CT or "centre tap" winding. The centre wire will be the wire that is disconnected when the other two wires show a maximum resistance reading.
If you find 4 or more wires showing continuity, it's probably a multi-tap mains input primary.
Once you've done this, you can see how many windings you've got, and what connections are which. Next, you need to find the voltage ratios. I find the easiest way to do this is using a small 6V transformer (the type used in cheap cassette recorders or portable radios). The theory here is that 6V is a low-enough voltage to not cause any damage to the windings.
Connect your 6V ac from the small transformer to a winding of your unknown transformer. Then carefully measure the ac voltages at the other windings. Switch off the power before changing the meter probes- say for example the winding you've connected the 6V to is actually a 6V winding, and then you touch another winding which is rated at 240V, then 240V will appear at that windings terminals!
You'll now have a voltage reading next to each winding. From this you can work out which winding is which. The mains winding is usually instantly recognisable- especially if it's a non-tube type transformer. With a lower-voltage type transformer, you'll see a massive ratio between one winding and all the others- this is the mains primary.
I hope this helps- I've managed to salvage many surplus "unknown" transformers using this method. Let me know when you've worked out which windings are which, and we'll see if we can work out the rest of the ratings.
Of course, the easiest method is if someone has a data sheet already for this model :wink:
Mark
Alrighty,
Well, I've got 2 red wires, 1 Black, 1 Black/White, 1 Grey, 1 Grey/White and one Red/Yellow striped.
The Red/Yellow shows continuity with both red leads
Measuring between the two reds = 14.82R
Measuring from the Red/Yellow to the Red(1) = 7.38R
Measuring from the Red/Yellow to the Red(2) = 7.48R
Measuring between the black and black/white = 137.08R
Measuring between the greys and grey/white= 137.08R
Now I'm lost, what next?
Thanks for the help!
Well, I've got 2 red wires, 1 Black, 1 Black/White, 1 Grey, 1 Grey/White and one Red/Yellow striped.
The Red/Yellow shows continuity with both red leads
Measuring between the two reds = 14.82R
Measuring from the Red/Yellow to the Red(1) = 7.38R
Measuring from the Red/Yellow to the Red(2) = 7.48R
Measuring between the black and black/white = 137.08R
Measuring between the greys and grey/white= 137.08R
Now I'm lost, what next?
Thanks for the help!
SSLtech
Well-known member
Here's my guess:
Primary 1: Black - Black/white 110V
Primary 2: Grey - grey/white 110V
Secondary Red - red/yellow - Red (center-tapped low-voltage)
My guess is that the white stripe wires are the same phase ending... for 240V operation join Grey to black/white and connect 240V across Black and grey/white. For 110V connect black to grey, and connect black/white top grey/white. Power should be applied across the commoned pairs.
Keith
Primary 1: Black - Black/white 110V
Primary 2: Grey - grey/white 110V
Secondary Red - red/yellow - Red (center-tapped low-voltage)
My guess is that the white stripe wires are the same phase ending... for 240V operation join Grey to black/white and connect 240V across Black and grey/white. For 110V connect black to grey, and connect black/white top grey/white. Power should be applied across the commoned pairs.
Keith
Mark Burnley
Well-known member
Yep,
Sounds good to me, and the resistance readings make sense too.
:thumb:
Mark
Sounds good to me, and the resistance readings make sense too.
:thumb:
Mark
