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Author Topic: Changing a 115v tranny to a 240v one  (Read 13286 times)

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scsibear

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Changing a 115v tranny to a 240v one
« on: Time Format »

Hey guys looking for some advice on this one..

I recently got a 19" rack unit from the US that runs on 115v, i live in Scotland so i'd like to change the tranny to a 240v one, my intention would be to also add an IEC socket on the back of the unit so i can plug it straight into my Furman power/strip board M10eX.

The tranny itself has only some info stamped on the top which is this 500 115 - 259 then below that it says EIA 606 - - 336.
I know from the EIA number that it was made by Woodward-Schumacher and the 336 is to do, with the year and weekly run i.e 3 (1983) 36 is week 36.

The 115 is the voltage not a clue what the - 259 is tho, and i am assuming the 500 is milliamps ?? yes/no ?

The primary on the tranny has 3 wires 2 black one going to an internal fuse and a green for chassis ground, the secondary side has 2 red wires and a yellow going to the board, that then runs to the full rectifier bridge with the 4 diodes.

I was thinking i'd need a 240v - 15v step down but not really sure what other specs i might need to look for...
I include a snapshot of the schematic for your perusal.

Any ideas folks ??

Regards
scsi

« Last Edit: Time Format by scsibear »
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rnolan

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Re: Changing a 115v tranny to a 240v one
« Reply #1 on: Time Format »

Hopefully MJMP can work out from the schematic how much power (VA) you'd need in a step down transformer ?  What sort of unit is it ? If it's a preamp or FX unit it wont need as much current as a poweramp so a 250VA step down transformer will be fine. On mine it says 115 AC 250 VA (volt amps) which also worked fine with a B200s poweramp.  We sourced an appropriate 240v toroidal transformer later and fitted it (B200s has room for a toroidal, not all cases do).  Bigger (higher output poweramps need a bigger stepdown transformer). Replacing the transformer is the best option though. otherwise you are now lugging 2 transformers around  :(
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #2 on: Time Format »

Is this for a furmann PQ-3?(according to the schematic).
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scsibear

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Re: Changing a 115v tranny to a 240v one
« Reply #3 on: Time Format »

Yes this is for the PQ3, I just need to make sure I get the secondary side the correct voltage even at 15v it may be too high, as the rectification and the smoothing will increase the voltage to the peak AC level and the regulation appears to be the two current limiting resistors and the zener diodes. If the transformer is too high those resistors and zeners will end up dissapating the extra power as heat, and i don't want that.

I think the best thing to do would be (as i do not have a 110V shaver socket in this house) is to buy a 240v - 110v step down adapter from ebay (it's a proper one made to run US voltages(mains 110v) from UK sources (mains 240v) and probe the two red wires from the secondary to see what the overall voltage is. That way if say it's 18v then i know i'd need a 9-0-9.

Have you any idea what the 500 115 -259 stamp on the transformer might be ?, specifically the 500 - is that 500mA ?
Regards
Ray
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #4 on: Time Format »

I don't think it's 500mA,it's just an EQ.Can you wait until tomorrow?I'll pop mine open en see what i have put in there.I rebuilded mine years ago to 220V.
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scsibear

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Re: Changing a 115v tranny to a 240v one
« Reply #5 on: Time Format »

Sure Marshall no worries thanks a bunch  :D
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #6 on: Time Format »

So just checked and it seems it draws around 45mA on the +15V rail and 41mA on the -15V rail.(see pic)

I also modified mine so it doesn't use zener diodes but I added a small pcb with a 7815 and 7915 regulator.(see pic)

I used a toroidal transformer with these specs, 2 x 15V/0.167mA

Hope this helps a bit.

BTW do you have the schematic of a PQ-3?
« Last Edit: Time Format by MarshallJMP »
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scsibear

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Re: Changing a 115v tranny to a 240v one
« Reply #7 on: Time Format »

Hey Thanks for the info and the pics, I had a brief look online for a transformer but i couldn't find one with so low mA's they all seem to be like 20mA and above, and i know absolutely nothing about toroidials at all, but at least i know for sure it's deffi 15v out, could you recommend which mA rating i should stay below ( I mean a safe range for direct replacement)

Also inside your unit looks totally different from mine, I can see most of the last Two EQ sections in you pic and there is no PCB there at all, in mine there's a board about 2 inches thick running the full length of the unit (see pic).

As regards the schematic yes i have, it also has the Stereo Mod included so here it is
« Last Edit: Time Format by scsibear »
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #8 on: Time Format »

I think my unit is a lot older and my pcb is different then yours.

Now for the transformer You need at least 50mA a side!!You don't need to stay below it but above it.

So I recommend something that has 2 x 15V 100mA or above.(3.2VA or 5VA)

I'm using this one   http://be.farnell.com/multicomp/mcfm50-15/transformer-toroidal-2-x-15v-5va/dp/9531530

The yellow pcb is not original,that's something I added.
« Last Edit: Time Format by MarshallJMP »
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scsibear

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Re: Changing a 115v tranny to a 240v one
« Reply #9 on: Time Format »

Thanks Marshall, I found the exact same one as you used on the UK Farnell site from you link, so i'll go order it now.
Yes i saw the yellow pcb add on what is that doing ?
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #10 on: Time Format »

Farnell also has a French devision btw.

Well that pcb is connected to the transformer,I added a full bridge rectifier,2 caps and 2 voltage regulators (7815,7915) so it outs out a steady +-15V to the furmann pcb.And got rid of the 15V zener diodes.
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scsibear

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Re: Changing a 115v tranny to a 240v one
« Reply #11 on: Time Format »

Ahh i see nice one, I think i'd have to go on an electronics course to be smart enough to know what i was doing with that kinda thing, I actually quite fancy doing a course, maybe i will look into it.

Ohh BTW i meant to ask, the On/Off switch on your unit, did you have to change that to a higher rating to take the 240V or was the original one still ok ?
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #12 on: Time Format »

Mine doesn't even have an on/off switch  :lol: just EQ on/off

It's a standard schematic,same is used in the MP-1,MB-1 etc...

http://www.eleccircuit.com/wp-content/uploads/2007/05/power-supply-regulator-15v-15v-1a-by-ic-7815-7915.2.jpg
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scsibear

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Re: Changing a 115v tranny to a 240v one
« Reply #13 on: Time Format »

Yes I see it, it is the same cool tnx  :thumb-up:
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MarshallJMP

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Re: Changing a 115v tranny to a 240v one
« Reply #14 on: Time Format »

They even sell these on ebay ready to go

http://www.ebay.com/itm/15V-1A-AC-DC-Regulator-Power-Dual-Supply-input-15-18V-7815-7915-Full-Parts-/301036463175
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