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Old 3rd March 2013, 02:35 PM   #1
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Default Transformer from Marshall 3530

Hello. My first post
What is a transformer in marshall 3530? Symbol on schematic are 07-272.
http://www.drtube.com/schematics/marshall/3530psu.gif
Or maybe somebody have this amp and make measured?
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Old 3rd March 2013, 02:38 PM   #2
kevinkr is offline kevinkr  United States
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Moved to Instruments and Amps as this is guitar amp related and I thought it much more likely to get a response here than in parts.

Welcome to the forum!
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Old 4th March 2013, 10:04 AM   #3
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Thanks
I'm waiting for answer.
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Old 4th March 2013, 08:09 PM   #4
Enzo is offline Enzo  United States
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The number you provided is the Marshall part number for it, if you ordered one from Marshall, that is what you'd ask for. Unfortunately since teh amap is 25 years old, it is very doubtfull Marshall still has them.

Your schematic section shows roughly 60v on the DC power supply rails, so that means roughly 42vAC on either side of the center tap, so basically an 80-85vAC center tapped transformer. I don't know the power output of that model offhand, so I cannot comment on the current requirements.
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Old 5th March 2013, 06:07 PM   #5
JMFahey is offline JMFahey  Argentina
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Agree and add: the amp is nominally 300W RMS so a transformer such as suggested by Enzo , with a 450 or 500 VA rating will be fine.
This in case you can't find the original Marshall one and need an off the shelf replacement.
You don't mention it but being a low 2U height rack cabinet, means it's probably a toroidal transformer.

Just curious: how do you know the transformer is bad?
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Old 5th March 2013, 06:57 PM   #6
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I have a Laney amp of similar era and spec.
Here's a quick photo of the transformer - outer diameter is around 5".

Click the image to open in full size.


I'd guess yours is something similar - go for 5-600VA and it'll be plenty enough. I'd try to avoid going much higher or it'll be adding a lot of weight for limited return.

Chris
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Old 7th March 2013, 07:37 AM   #7
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Thanks very much for answers

Quote:
Originally Posted by JMFahey
Just curious: how do you know the transformer is bad?
I have only chasiss and preamp from this amp. So, I try to find rest parts (Is any chance? Some good web pages where to find?) or build from schematic.

I found picture this amp:




Click the image to open in full size.
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Old 7th March 2013, 11:38 AM   #8
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The Laney amp picture shows 8 pin IC's. This means any amp with op amps on the preamp will need a power transformer with +-15V winding. In the USA, Antekinc.com sells this sort of power transformer, with +-80 and +-15 windings. Connexelectronic in south China sells a high frequency power supply with this sort of output, but you would need to box it up in its own metal case to stop radio wave interferance.
eserviceinfo.com has schematic diagrams for marshall3510 and marshall3560, perhaps your amp falls in between in power output. The final power output has to do with size of transformer and heatsink, and number of output transistor pairs. I find surplus heatsinks in old factory motor drives, also containing 24 VDC fans and relays, and a good source of 400 v long life high temperature electrolytic caps. Using 400 v caps at 160 VDC is a waste of cubic space but shouldn't hurt their lifetime much.
The best bargain in the USA of output transistors is the MJW21193-4-5-6 but drilling the heatsink for the TO3 package like in the picture is a nuisance. One hole TO247 transistors are MJL4302 and MJL4281. They withstand about 4/5 the wattage of the TO3 ones. If you're in the orient, some people like the 2SC5200-2SA1943 as an output transistor complementary pair in TO247. These are 3/5 the wattage of a MJ21193. Datasheets in English are on datasheetcatalog.com
Good luck on your project.
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Last edited by indianajo; 7th March 2013 at 11:57 AM.
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Old 7th March 2013, 07:57 PM   #9
JMFahey is offline JMFahey  Argentina
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OK, I see.
So it looks like somebody gutted the power amp and PSU and left chassis and preamp?
Let me make one suggestion: you do not *need* to put a 300W amplifier there.
Specially because you will not have problems getting a proper toroid in there, but I remember that amp (I repaired a couple from that family) was based on a quite clever "heat box" (which can be seen in the picture) which housed and cooled the power transistors while it was continuously injected fresh air with a fan.
Not something easy to duplicate at home, and the original layout simply does not consider conventional heatsinks as those in the Laney.
Personally I would consider it a gift (well, I guess it was ) and mount there whatever fits and allows me to play Bass.
Being 2U high it will easily accept a conventional EI transformer good for a 100/120W power amp, and said amp would fit comfortably there and not dissipate much heat.

Trying to clone the original amp will be very expensive because of the unobtanium MosFets, besides the "mechanical" problems I mentioned.
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Old 30th May 2014, 09:26 PM   #10
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Default Power to pre amp

Hi I actually own one of these I must say I have found the power amp side of things quite unreliable, its for this reason that I would like to build a power supply just to power pre amp, i see that the pre amp has the voltage regulator so I guess its just a case of finding a transformer to supply the power to the pre amp via a bridge rectifier? and this is my question what size transformer do I need will anything over 15v work and then what is a suitable amperage?? hmmm Cheers in advance.

PS i have a working 07 272 if you're still interested



Thanks

Phil.
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