MARSHALL MG15CD POWER TRANSFORMER SUB

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MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 01 Jul 2019, 06:24

hello

ive got a marshall mg15cd but the power transformer is busted now, the power transformer of it is 16v-0-16v 2 amp.

can i substitute it with 15v-0-15v 12 amperes transformer??

any advice???
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby Manfred » 01 Jul 2019, 09:01

IMO it should work.
Connect the transformer temporay and see if it works correctly.
I suppose that the 12A transformer is is much larger than the original one,
is there enough space to install it?

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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby thetragichero » 01 Jul 2019, 20:44

quick Google search only got me yup mg15cdr but i didn't see any voltage regulators that might not like the slightly lower voltage. the circuit will only draw as much current as it needs but as long as it fits physically I'd say it's a go

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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby plush » 01 Jul 2019, 20:55

thetragichero wrote:quick Google search only got me yup mg15cdr but i didn't see any voltage regulators that might not like the slightly lower voltage. the circuit will only draw as much current as it needs but as long as it fits physically I'd say it's a go


Mg15 series use 15v zener diodes to achieve +/-15v from 16v AC rectified to +/- ~21volts. So, i believe it's 100% okay to replace said transformer, if it fits, ofcourse.

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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 02 Jul 2019, 01:50

Manfred wrote:IMO it should work.
Connect the transformer temporay and see if it works correctly.
I suppose that the 12A transformer is is much larger than the original one,
is there enough space to install it?


thanks for the reply..but how this thing work?even its a higher amperage?? but im excited to do this substitution, and im little bit nervous it might explode the transformer or the preamp?? haha
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 02 Jul 2019, 01:57

if i will use the 15 volt 12 ampere transformer is there a bad will happend will pass thru four rectifiers diode 1n4006 on the power section ???
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby george giblet » 02 Jul 2019, 04:29

if i will use the 15 volt 12 ampere transformer is there a bad will happend will pass thru four rectifiers diode 1n4006 on the power section ???

It shouldn't be a problem *under normal use*. However, if you get a fault somewhere then the fault current of the 12A transformer is going to be a *lot* higher than the 2A transformer. It *may* take out a lot more stuff, like fry PCB tracks.

As far as it working is concerned, the change from 2A to 12A is probably OK. What normally happens when you put in a larger transformer is the voltages under no-load are lower but the voltages under full load are higher. So you might find the output power for transient signals is *lower* for the larger transformer but the output power for continuous signals is higher. What that means is for continuous signals the amplifier is stressed out more. If the amp design is already stressing the parts it could push it over the edge. The fact your larger transformer is 15V and not 16V might help keep it in the safe zone.

The bottom line is there's always a small risk when substituting parts. In this case it would be fairly low risk.
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby Manfred » 02 Jul 2019, 06:56

I forgot to mention that it possibly necessary to increase the rating of the primary fuse,
because the inrush current is higher using the 12Amps transformer and the original fuse may be blown.
In this case it would be good to hook in a secondary fuse, because the secondary transformed current that triggers primary fuse is six times higher too
and can burn the wires and conductor strips.
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 02 Jul 2019, 07:37

Manfred wrote:I forgot to mention that it possibly necessary to increase the rating of the primary fuse,
because the inrush current is higher using the 12Amps transformer and the original fuse may be blown.
In this case it would be good to hook in a secondary fuse, because the secondary transformed current that triggers primary fuse is six times higher too
and can burn the wires and conductor strips.



thanks again..by the way what fuse i will use now? 12ampere fuse?? same as the amperage of the transformer??

its kinda dangerouse to imagine.. i think its risky to use a 12 ampere transformer whoaa my amp gonna double shot dead!!
its gonna be problematic again..my pcb strips will gonna burn?? whoaa
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby Manfred » 02 Jul 2019, 14:31

thanks again..by the way what fuse i will use now? 12ampere fuse?? same as the amperage of the transformer??

its kinda dangerouse to imagine.. i think its risky to use a 12 ampere transformer whoaa my amp gonna double shot dead!!
its gonna be problematic again..my pcb strips will gonna burn?? whoaa


What are the data of the 12 Amps transformer, is there an imprint on it.

Is the current rating 12 Amps for each output winding or for both windings?
How is the primary voltage of the transformer?
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 03 Jul 2019, 11:22

Manfred wrote:
thanks again..by the way what fuse i will use now? 12ampere fuse?? same as the amperage of the transformer??

its kinda dangerouse to imagine.. i think its risky to use a 12 ampere transformer whoaa my amp gonna double shot dead!!
its gonna be problematic again..my pcb strips will gonna burn?? whoaa


What are the data of the 12 Amps transformer, is there an imprint on it.

Is the current rating 12 Amps for each output winding or for both windings?
How is the primary voltage of the transformer?



sir i never done it or connecting the 12 amp transformer yet on the main board..i was kinda imagining if theres something happend anyway can you suggest what rating of the fuse should i put to the power rail to the primary??
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby Manfred » 03 Jul 2019, 11:37

sir i never done it or connecting the 12 amp transformer yet on the main board..i was kinda imagining if theres something happend anyway can you suggest what rating of the fuse should i put to the power rail to the primary??


I need the data to answer the question, there is no simple answer to that.
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby thetragichero » 03 Jul 2019, 13:42

it may be a guess, but the op may not know what data you are asking?

I'm kinda curious because i have a TON of power transformers salvaged from old solid state organs that I'd love to be able to get specs on
i can hook it up to mains and read voltage on the secondaries (which i know is dangerous), and i can measure the resistance of the windings (but not know what use the information is for) but in terms of current handling capability i have no idea
markings are generally worn or provide no information upon googling
anyway i am eager to see what new information i can pick up!
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby Manfred » 03 Jul 2019, 20:00

it may be a guess, but the op may not know what data you are asking?


Hi thetragichero,

that was my question posted yesterday, it is still not answered.

Is the current rating 12 Amps for each output winding or for both windings?
How is the primary voltage of the transformer?


I don't know where Ballfire live, therefore I don't know the main voltage at his residence.
You are right, perhaps I did not make myself clear in my post.
What I meant was two Windings with 15 Volts and 6 Amps or 30 Volts with center tapping ans 12 Amps.

Only with this two informations I can determine the fuse ratings.
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 04 Jul 2019, 01:57

Is the current rating 12 Amps for each output winding or for both windings?
How is the primary voltage of the transformer?


I don't know where Ballfire live, therefore I don't know the main voltage at his residence.
You are right, perhaps I did not make myself clear in my post.
What I meant was two Windings with 15 Volts and 6 Amps or 30 Volts with center tapping ans 12 Amps.

Only with this two informations I can determine the fuse ratings.[/quote]


this is my transformer look like..see my illustration..below

i use the 220volts wiring because our mains is 220volts, the 110v is optional..
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby phatt » 04 Jul 2019, 10:32

If you are worried about melting the circuit then you can just put fuses in line with the two secondary rails,, many designs use fusing on the rails which is a good idea anyway. :thumbsup
That will stop any short from melting stuff.
I'd guess being a very low wattage amp design the fuses may only need to be small.
Start at 500mA and go larger if they blow at turn on. Others here may know better ways to work out fusing. :scratch: But that is how I do it.
Phil.

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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby Manfred » 04 Jul 2019, 12:12

Here my personal recommendation:
Fuses12AmpsTransformer.jpg
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby george giblet » 05 Jul 2019, 04:04

this is my transformer look like..see my illustration..below

i use the 220volts wiring because our mains is 220volts, the 110v is optional..

We still don't really know if the 12amps applies 15V or 30V.

If it's 12amps at 30V that makes it a 12*30 = 360VA transformer. Which is enormous.
Whereas 12 amps at 15V makes it 12*15 = 180VA transformer which is smaller.

If you could measure any, or even better all, of these it would help narrow it down:
- the size of the *iron core part* : width x depth x height
- the resistance of the primary (220V windings)
- the weight of the transformer.

A 180VA will probably work fine with a T0.5AL 250V (0.5A slo-blo) fuse. Depending on specifics a 0.5A might blow after 1000 turn-ons or but a 0.6A or 0.7A will reduce the chances to 10000 turn-ons. There's probably enough protection to warrant not using the 2A secondary fuses.

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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 08 Jul 2019, 03:12

Manfred wrote:Here my personal recommendation:
Fuses12AmpsTransformer.jpg



good day sir..

maybe im gonna tr this one..but i will take and study it first and test it...

thank you sir..
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Re: MARSHALL MG15CD POWER TRANSFORMER SUB

Postby ballfire » 08 Jul 2019, 05:16

phatt wrote:If you are worried about melting the circuit then you can just put fuses in line with the two secondary rails,, many designs use fusing on the rails which is a good idea anyway. :thumbsup
That will stop any short from melting stuff.
I'd guess being a very low wattage amp design the fuses may only need to be small.
Start at 500mA and go larger if they blow at turn on. Others here may know better ways to work out fusing. :scratch: But that is how I do it.
Phil.



thanks you sir i will try your advice also
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