mystery power transfomer - measuring voltages across all secondaries

[boroman]

So brown/black to yellow is it's own separate winding. It could be primary or secondary, there is nothing that says all primary have to be on one side physically. Some transformers have secondary wires on both sides, etc.

Like eschertron suggested above, you need to apply voltage somewhere and measure voltage at all the windings. For safety, it is preferable to start with a low AC voltage applied, like a 6.3V heater supply from another amp, or a low voltage AC wall wart type adapter.

I'm 100% sure one side are primary and the other secondary (just before my 110/120/220/240 power switch broke it was wired to "tube socket-like" switch)

[g1]

I'm 100% sure one side are primary and the other secondary (just before my 110/120/220/240 power switch broke it was wired to "tube socket-like" switch)

Then the 2 separate windings on the primary side are most likely used in series for the 220/240, and parallel for the 110/120. The trick is getting the phasing correct so the voltages don't cancel out.

[Helmholtz]

Here's what I would do:

1) Isolate all wires and tape them to a piece of cardboard, wood etc.
2) Connect the heater voltage from another transformer via a 22R/5W series resistor to the brown wires.
3) Measure the voltage across the brown wires, if around 7V....
4) Measure all winding voltages

5) Once you've found the correct primary configuration, connect to your mains via a (60W) bulb limiter and measure all winding voltages.

Unloaded secondary voltages might be high by ~10%.

Do you remember anything about the mains selector switch wiring?

[boroman]

Here's what I would do:

1) Isolate all wires and tape them to a piece of cardboard, wood etc.
2) Connect the heater voltage from another transformer via a 22R/5W series resistor to the brown wires.
3) Measure the voltage across the brown wires, if around 7V....
4) Measure all winding voltages

5) Once you've found the correct primary configuration, connect to your mains via a (60W) bulb limiter and measure all winding voltages.

Unloaded secondary voltages might be high by ~10%.

Do you remember anything about the mains selector switch wiring?

So, If I understand correctly, I am connecting it other way round to get "right" voltage reading at primary side, e.g. in my case 240V?
So other working/known transfomer with heater voltage, and its each 6,3V wire connected with 22R/5W to each brown wire of the unknown transformer?

1st wire working OT 6,3v ----> 22R ----> u/o PT brown wire 1
2nd wire working OT 6.3v ----> 22R ----> u/o PT brown wire 2

Like that?

Why I need to put resistors there?

[Helmholtz]

So, If I understand correctly, I am connecting it other way round to get "right" voltage reading at primary side, e.g. in my case 240V?

Yes. Transformers work both ways
Is 240V your nominal mains voltage?

So other working/known transfomer with heater voltage, and its each 6,3V wire connected with 22R/5W to each brown wire of the unknown transformer?

1st wire working OT 6,3v ----> 22R ----> u/o PT brown wire 1
2nd wire working OT 6.3v ----> 22R ----> u/o PT brown wire 2

Like that?

Why I need to put resistors there?

One 22R series resistor is sufficient.
Its purpose is to protect the "donor" transformer from potential shorts.

[eschertron]

I'd think 1 resistor in the circuit would be sufficient. That is used for current limiting to protect life and property if something goes amiss during the test.
6.3v / 22R (short circuit on the test side) = under 300ma load on the supply transformer. That's protection for the 6.3v winding on the supply.
Also current limits the unit under test, if you short (or grab) two wires with a potential across them.

edit: simulpost

[boroman]

Yes, 240 is my main wall voltage.

So, Only one 22R resistor no matter on which one wire. Allright. I could use also fuses there, right?

So, I'd need to find two wires on the primary side that have approx 120V and join them together to have 240 primary? (+/- 10% of course, no load)

[boroman]

OK. I tested it that way, and voltages from the primary side seems even lower than 6VAC.. Then i checked voltage AFTER resistor and it has dropped to 0,2V (that would explain things) + resistor gets super hot... hm?

[Delta362]

Did you apply the 6.3V from your source thru a 5 watt resistor to one of the thick brown leads, and the other thick brown lead went back to the other end of the 6.3V source? Just verifying where you applied the voltage.

Was your 0.2VAC measured across the two thick brown leads of the test transformer? If so, that would indicate that the thick brown wires are shorted.

[boroman]

Yes, like on the pic below:

[Helmholtz]

If the resistor and the solder connections are good (soldering doesn't look great), you have a short somewhere and the resistor should get hot.
Could be some PT wires touching or an internal winding short.
In any case the heater winding (as well as all other PT windings) will look like a short.

I see you used an ancient 40R/5% resistor probably rated for no more than 2W. The test sholuld work nonetheless.

[g1]

Are all the other wires taped off so they can not touch each other?

[boroman]

Yes, everything is "in the air"... I havent got time yesterday to look closer, but will do tonight and post results here