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amoncarter 19th August 2003 12:36 AM

another 220v to 110v question
I found the exact opposite of what I'm trying to accomplish through the search function, but it helped nonetheless.

The unit is a Bose 901 equalizer from 1993 and I had Bose rewire it from 110v to 220v and now I want to change it back. It uses a (Markings: Pikatron D 6390 USINGEN NP 1076 QV 120993) transformer that currently is wired (on the primary) to the incoming wires on its outside taps and the 2 inside ones are shorted to create a series connection. It leads me to believe I have 2 equal windings together handling the 220v.

My question is: Can I disconnect the series connector and wire the 2 primary windings in parallel - to get it back to 110v operation? or is that a bad assumption? are there any gotcha's in phasing etc.?

sorry, i'm a rank amateur and it's been 20+ years since I've done this..I could of course send it back to Bose but on principle and pride feel I've already paid once to do this and I should be able to do it myself...:cannotbe:

trwh 19th August 2003 07:51 AM


You're quite right in saying you should be able to connect the primaries in parallel for 110V operation. Again, you are also right in assuming there are gotcha's with phasing! You must make sure that the beginning and end of the two windings are connected together, not vice versa. This should be quite simple since you already have them wired in series - the end of one winding will currently be connected to the beginning of the next, so you can work out what connection you need.

There may also be a mains fuse value to change. If this is so, it would involve a current rating increase. Try and determine what the present value of the fuse rating is and see if it's appropriate for the power drawn by the unit for 110V operation.

Take care,

PS - Maybe Bose could provide a service manual that would help?

EDIT: Just so I'm clear, I mean both the winding beginnings and both the winding ends connected. :)

dhaen 19th August 2003 08:14 AM


Your assumption is correct. The phasing of the windings is of course vitaly important, but easily determined by deduction:
Lets call these primaries winding A and winding B.
At present, one end of winding A is connected to one end of winding B.
Disconnect that end of winding A, and connect it to the other end of winding B.
The 2 remaining winding ends can then be connected.

Clear as mud?


moamps 19th August 2003 09:54 AM

2 Attachment(s)
1 picture>=100 words

dhaen 19th August 2003 10:08 AM

Thanks Moamps :)

amoncarter 19th August 2003 01:01 PM

Very clear, and extremely gracious of you all. thanks.

amoncarter 20th August 2003 03:21 AM

worked, I now have a 110v equalizer. thanks.

alipper 11th July 2010 09:11 PM

Thanks for the advice. I just converted my Bose 901 Series VI equalizer from 220V to 110V. Here are some specifics. Next to the primary of the transformer (the side where the power cord is soldered), there are three places for jumpers. For 220 volt operation, the one labeled LK1 is installed. To convert to 110 volt operation, remove the LK1 jumper. There are two spots (without jumpers in them, but with lines indicating there could be one) labeled 1-2 and 3-4. Next solder a jumper from hole 1 to hole 2, and a second jumper from hole 3 to hole 4.

I tested mine by checking voltage at testpoints indicated on the PCB for GND, +15V and -15V (located in the area behind the switches).

Hope this helps someone.


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