MkIV Export Mains Transformer.

[austinlegro]

I find the following hard to believe.

My Early MkIV needs a new mains transformer.

Part# 561137 EIA 606-237

My repairer has chased the UK distributor who have in turn chased Mesa and got the reply "no longer available, peculiar to early MKIVs, might be of fender origin then again might not be.."

Can anyone on this board point me in a useful direction?

 

[SpongeRob]

Hi Austinlegro,

sorry to hear about your MKIV Transformer

Well i don't know where you should search. If Mesa don't have them it should be very hard to get an original Transformer.
What about a replacement Tranny. There should be somewhere a Mains Transformer for the Mark Series. Actually they won't be original, but it would be the first i would think about. Or maybe it could be rewired. I once had my Transformer from my old Marshall rewired. But i heard it's not possible with every Transformer. But best is to find some useful information on the web about rewiring. The costs are the same as for a replacement Tranny.

Maybe some Forum members also have some useful information.

 

[austinlegro]

What I can't quite understand, and I would love some enlightening, is that I have 2 identical MKIV's, both MKIVb one 1992 (broken) and one 2009 gigged every week.
The only difference is that the 1992 has a fixed power lead, the 2009 a IEC plug.
Other than that they appear identical and I can't understand why I can't use a current MKIV transformer 561141 instead of the broken 561137
What are the differences, can the old amp be altered to run the newer transformer.

Apparently I can get transformers for any Mk1-Mk5 but not for a 1992 MKIVb. Is that correct??

 

[SpongeRob]

Okay! My fault. I just get it wrong.

A tricky question. I think some of the Mark IV guys or maybe Boogiebabies can give you the right answer. All i remember if i'm not mistaken: 561137 is the Export Transformer from the MK IV A. The 561141 is the Export Transformer from the Mark IV B. But don't know if they're the same.

 

[Blueracer]

Sorry to hear about your transformer going south. Bummer. I took a quick look at the schematics for the Mark IVa and Mark IVb. The difference in the two power tranformers as far as I can see is that the 561141 transformer has a 12 vac secondary tap that the 561137 doesn't. All things being equal (and sometimes they aren't) you should be able to use the 561141 as a replacement and not use the 12 vac tap as it isn't necessary for the Mark IVa. The only caveat I would suggest is to confirm that the current handling capablilities of the secondaries for both transformers are the same or that the 561141 exceeds that of the 561137. I would give Petaluma a call on this or if you like I can call them for you and confirm the above. Let me know if I can help.

 

[Blueracer]

A second closer look did reveal another difference between the two transformers. The 561141 has a center tap on the filament tap and the 561137 does not. You still should be good to go as the Mark IVa does not use the center tap for the filaments (ground reference is formed by a pair of 100 ohm resistors, standard stuff). Hope this helps.

 

[austinlegro]

Thank you all for your replies so far..

Just to confuse you all, and get to the nub of the problem, my broken transformer is labelled 561137 but the amp is definitely an early B, satellite send etc not an A, twin effects loop etc

Even more annoying the previous original owner, bought it new, used it solely for bedroom use and never took it out the house.

 

[SonicProvocateur]

I wonder if he soaked impedance alot? I've seen more than a few Marks for sale on evilbay rigged 8-4ohm and i'd steer clear of those, wondering just how many hours/volume they've been soaking.

Only time I ran a IVa head mismatched ONCE (accidentally) into a 4x12, it blew an EL34 in about 20 minutes of high octane shredding.

 

[SpongeRob]

Well the early MK IVB could have the main transformer from the old "A" Series which were leftover during the production. So this wouldn't confuse me. There are also Mark III with IIC+ PT's and OT's. So it could be a very early B version.

 

[austinlegro]

It's very early, #5854

Did the early MKIVb and the later MKIVb have revised wiring then and the need for different secondary tappings?

 

[Blueracer]

I will try again. The 561141 has more output taps than the 561137. You should be able to use it as a replacement as some of the output leads just aren't used in your amp. It doesn't matter about Mark IVa or Mark IVb. What does matter is what the original transformer is and what the replacement is. As long as the output current capability of the 561141 is equal to or above the 561137 you should be good to go. Oh it should have the same dimensions as the original also so that it fits in the chassis.

 

[austinlegro]

Thanks for you replies and especially Blueracer for your patience.

I shall chase Mesa for a definitive 'this part is obsolete, use this newer part instead' which either my UK agent was incapable of doing or the manufacturer was reluctant to say.

I can't be the first person to need a replacement 561137

cheers