Another "can I use this transformer?" thread

[silver1omo]

I have a trafo from a sharp subwoofer amp (using a stk412-400) that I would like to repurpose for a chipamp.
It has 5 cables in the mains and 7 in the secondaries.

Mains: Blue, brown, orange, white and red.
Secondaries: 2xred, 2xblue, black and 2xyellow.

The amp has a board with a rotary voltage selector (110v, 127v, 220v and 230-240v) and fuses. The power cable is 2 pronged with no ground.

In the secondaries, if I measure red-blue=21V. Blue-black=21v and red-black=42. The yellows are together and measure 15v (all this idle).

I tried goggling the number stamped in it and was unable to find anything useful.

Do you think it could be used?

[srinath]

The voltages from it should match the one you need for your chip amp.
I have several trafo's waiting for their chip amps, and several chip amps waiting for their trafo ... I have 3-4 amps I am still hoping will come back to life, onkyo 555, teac ag-v890, pioneer vsx1020 to name a few ... and I need something like a 29 0 -29 trafo for a lm 3886 based amp, and I just located the right trafo that I have liberated from a combo box system ...
I want to stuff the chip amp inside the teac chassis, not get the trafo out, cos that thing only has a bad power amp, the tuner, the whole rest of it works great including the remote ...
I have a few more, I cant remmeber it all ... all I can say is ... a 30 0 -30 v 300VA capacity whether you pull it from an amp or buy it from the store are about the same. Yea toroidal isn't the same as EI isn't the same as bobbin core etc etc, but for a power transformer it doesn't matter a whole lot as long as its decent quality and your pic looks very good, fuses for each output line and what not ... similar to what I would be using I'd say.
Anyway Just my opinion, wait til la few more people post. I am not an electrical tech, just a man with a soldering iron and a dream.

Cool.
Srinath.

[wazzy]

Check your voltages using black as your reference ie blue black, red black, on either side of black, I suspect that black may be your centre tap. If so it may certainly be useful.

[AndrewT]

Find out which wires are on the same winding.
Build a mains light bulb tester (dim bulb tester).
Insulate every wire end to prevent accidental shorting.
Use the bulb tester to power up the primary of the transformer.
Tell us what the bulb did.

[silver1omo]

I just realized that the PCB has markings on the mains.
Blue 0v
Brown 110v
Orange 240v
White 220v
Red 127v

So I'm guessing it is a multi-tap. I'll make a dim bulb tester and see what I get.

Thanks guys.

[silver1omo]

Originally Posted by wazzy

Check your voltages using black as your reference ie blue black, red black, on either side of black, I suspect that black may be your centre tap. If so it may certainly be useful.

I did include that in the first post:
Red-blue=21v
Blue-black=21v
Red-black=42v

Well, I checked/disassembled the voltage selector (4 pos rotary switch) and when you select 110v it uses the mains blue and brown. The path includes a 4A 250v fuse.
I'll test with the bulb and see if I get confirmation

[srinath]

Its a 21, 0 -21 red blue black trafo. Centertapped 42v red to black with blue being the center. Also make sure it can give you the needed amperage.
Cool.
Srinath.

[srinath]

I have a trafo that is center tapped on the input side as well (obviously due to the 220/110v deal), its not used on that trafo in the amp it was in, but I have weird needs now, so I may try to use it backwards ... Let me see what it looks like when I try it backwards.
Cool.
Srinath.

[silver1omo]

Well, I tested for continuity on the secondaries and any pair I select (red to blue, black to red or black to blue) rings.

[gootee]

Originally Posted by silver1omo

Well, I tested for continuity on the secondaries and any pair I select (red to blue, black to red or black to blue) rings.

(By "rings", I assume that you mean that the meter makes an audible tone, when there is continuity, instead of meaning that there is a damped oscillation being seen on an oscilloscope display.)

That should be OK, if it's one big winding with an actual center tap, instead of two separate secondaries, which is what it must be if there are only three wires for the secondary.

Try measuring the resistance (Ω) between each pair. The resistance should correspond with the length of the wire being measured.

There should be two pairs with lower resistances and one with a higher resistance. The wire color that is in both of those pairs with the lower resistances should be the center tap. The pair with the one higher resistance of the three should not include the center tap, since the higher reading should be from one end of the secondary to the other end, and should be about double the other two measured resistances, in this case.

(If the resistances are extemely low values, then remember to short the probe tips together, to measure the instrinsic resistance, and then subtract that from your measurements.)