Help Me ID This Transformer

[blown240]

I got this output transformer for an amp that I am building, But I have no idea what it is, or what each wire does.

The only markings on it are LO-0117A

There are 7 wires total coming out if it and 2 more that were cut off.  The wire with the masking tape is labeled 8 or possible has the infinity sign on it.  The wire with the blue tape is marked 4.  

How can I tell what wire does what? Or what exactly I have here, specs, etc...  Sorry, but I am really new at this.  The only testing tool that I have is the voltmeter that is in the picture.

Thanks!!

[sluckey]

First thing to do is identify all wires as they relate to windings. IE, use your ohm meter to determine which wires have continuity or resistance to other wires. Put one lead on one wire (any wire) and check for resistance to every other wire. Group all wires that have any resistance reading to the first wire. Either twist together, tape together, or put a cable tie around the group. There should be some more wires left over. Repeat the above process to find all wires that have continuity to other wires again. Hopefully you'll only have two groups, but if you still have wires left over, repeat this process again.

If you have more than two groups, the transformer 'may' not be an output transformer, or may be a special case OT. I'll assume you only have two groups and this is really an output transformer. One group will have a low resistance (only a few ohms or less than 1 ohm) reading between wires. This will be the secondary winding. The other group will have a higher resistance (maybe a few hundred ohms) between wires. This will be the primary winding.

Report back with your findings and the measured resistance readings for all wires. Then we can go to the next step.

[RicharD]

At a glance, it loos like a small push pull OT with a feedback winding, but take that with a grain of salt.  Follow Sluckey's advice and ohm everything out.  Wire markers can be a big help keeping thangs organized.  If the red, brown, and blue wires ohm out together, it's fairly safe to assume it's a push pull OPT.  If all the remaining leads ohm out together, it's a multi tap secondary.  Once you've established the individual coils, you can apply a small AC voltage in and measure the other leads to establish the voltage ratio which = turns ratio.  From there you can calculate the impedance ratio which is turns ratio squared times the load impedance.  Be sure to ohm out to the shell in case there is a short.  If any lead does not ohm out, it may be blown open.  As for wattage, you have to use your best judgement ie. guess.

[blown240]

OK, there are 2 groups of wires.  1 group of 3 and 1 group of 4.

Here is how they Ohm out:

Group of 3 has 2 light wires and 1 dark:

Light 1 to Light 2 = 207 ohms
Light 1 to Dark = 403 ohms
Light 2 to dark = 196 ohms

Group of 4 has 1 dark wire, 2 light wires, and a reddish wire:

Light 1 to light 2 = 1 ohm
Light 1 to Dark = 1 ohm
Light 1 to Red = 1 ohm
Light 2 to Dark = 1 ohm
Light 2 to Red = 1 ohm
Dark to Red =  1 ohm

Also in the group of 4 the 2 light wires have tape on them. 1 labeled 4, the other 8.

Here is my guess:

Group of 3 wires are the primary and the dark is the center tap.
Group of 4 wires dark is ground, red is 16 ohms, and the 2 light are as marked

Am I right here?

[sluckey]

Light 1 to Light 2 = 207 ohms
Light 1 to Dark = 403 ohms
Light 2 to dark = 196 ohms

The highest reading has to be between the two outside wires of the winding. That means "Light 1 to Dark = 403 ohms". And that leaves only Light 2 to be the center tap.

[RicharD]

Right on!  So it looks like a little push pull OPT with 3 secondary taps.  Hopefully you have a lamp limiter and a filament transformer laying around.  A screw type barrier strip would safety thangs up a bit.  What you wanna do is put a lamp limiter between the wall and the known filament transformer.  Connect the secondary of filament transformer to the light 1 and light 2 leads of the 3 group.  Cap off the dark wire.  You are going to measure all the secondary leads so this is where you'd wire in the barrier strip.  Masking tape and a scrap of wood will work in a pinch.  If the secondaries are linear, ie. 4 ohm, 8 ohm, 16 ohm, then you should read a similar AC voltage between pairs.  What you are trying to establish first is which secondary wire is the common.  Most likely it's the black wire.   From the common to 1 wire you should read a low voltage, to the second, somewhat higher, and to the 3rd some what higher.  (example:  common, 1V, 2V, 3V AC).  Use an accurate scale on your meter.  be sure and accurately measure the supply voltage too.  Don't assume it's 6.3V just cuz that's what the label says.  Vin / Vout = turns ratio.  Once you know this, you can calculate impedance ratios. 

[blown240]

ok so I made this:




its a preamp transformer into my output tranny.   I am getting 7 volts from the preamp trans, but I am getting nothing from the output trans.  I tried to use all 3 different combos on the primary side, and still I get nothing out.   My meter may not read below 1 volt though since its used for general electrician wiring...

[blown240]

OK, so I used the other side of the preamp trans.  134 volts out.  On the output trans I got 6, 8, and 13 volts.  6v was on the wire that said 4, 8 on the wire that said 8, and 13 on the red wire. this was using light 2 and dark from the set of 3 wires, or the wires that had 196 ohms resistance.

If I wire the primary different I get roughly half the output, or if I wire it the 3rd possible way I get similar results to the first test.  Hopefully that makes sense....  The primary wires withe the highest resistance, have the least output.  and the other 2 are pretty close to each other.

[sluckey]

Don't forget, 'Light 2' is the center tap. You'll need to put a lot more voltage into the primary if your meter can't accurately read less than 1 VAC.

[blown240]

dark to light 1  gives me 3,4,6 volts
dark to light 2 gives me 6,8,13 volts
light 1 to light 2 gives me 6,9,13 volts

does that make sense?  I am not sure we have the center tap correct, Or I don't understand something here...  shouldn't the center tap give me less voltage? 

[RicharD]

This may not be a PP transformer.  Single ended ultra linear perhaps?  That just doesn't seem likely at all.  I'd run the experiment again.

If your numbers are correct:
134V in & 8V out on the wire marked 8ohm gives a turns ration of 16.75 to 1.  16.75 squared times 8 ohms gives a reflected impedance of 2244 ohms.  Call it a 2k transformer.

[sluckey]

Maybe this will help identify the primary CT...

[blown240]

Ok.  What does that mean?  Sorry but this is all new to me.

[blown240]

Sluckey, I just now saw your picture.  Does it make sense that the center tap puts out more voltage.  It may be perfectly normal. I just dont know that much about transformers, but I have already learned a ton!

[HotBluePlates]

It means that based on your resistance measurements, Richard's drawing identified the wrong wire as the center-tap. If your highest resistance reading is between 2 given wires (you said this is between Light 1 and Dark), then those are the outer leads of the primary; that leaves Light 2 as a center-tap. That is what Sluckey's drawing depicts.

If Sluckey's drawing is correct, and you apply your test voltage to Light 1 and Dark, your output voltage should be higher. If they are, then Sluckey's diagram is the correct one. we can go from there to figure winding ratio and likely impedances.

[blown240]

Light 1 to dark gives me half the voltage of light 2 to dark, or light 1 to light 2.

Does it boil down to me using the 2 wires that give me the highest voltage as the outer leads?  If so then light 1 to light 2 is slightly higher.  I guess it makes sense to have the dark wire the center tap.

[RicharD]

>Light 1 to dark gives me half the voltage of light 2 to dark, or light 1 to light 2.

This means Light 1 and dark are your outer leads (brown and blue typically), and light 2 is your center tap (red typ.).

>Richard's drawing identified the wrong wire as the center-tap.
My drawing is wrong.... fancy that.  Sluckey's is correct.

[blown240]

Perfect!  Thank you guys very much for your help!

[sluckey]

Does it make sense that the center tap puts out more voltage.

ABsolutely!

It can be confusing when dealing with transformers, turns ratios, resistance, etc. Hopefully this simple drawing will drive home the idea that applying a voltage between center tap and end of winding will cause a BIGGER voltage on the secondary than you would get by applying the same voltage across the entire winding. I used simple numbers in my drawing to make it easier to get the concept, but the principle applies to your transformer as well.

Your resistance readings proved that wire "Light 2" is your center tap. And your voltage readings offer further proof that the wire "Light 2" is the center tap.

[blown240]

Very cool.  Thanks for taking the time to do the drawing.  Makes sense to me now!

[kagliostro]

Nice exposition

Skuckey, can I suggest you to add this to your Scrapbook

Kagliostro