Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: etarist on November 21, 2012, 05:53:16 pm
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Hello tube masters;
I am by far not part of your league but found this forum in search of help.
I have a Mesa 20/20 tube power amp with a blown
mains power transformer and wonder if it can be resurrected?
Mesa Boogie wants $300.- plus shipping for the original.
That's an impossible number for me.
The amp is only 1rack unit high,
so it's difficult to find a slim replacement transformer.
I wonder if it would be feasible to have the trans re-wound?
Here's a link to the amp shem.:
http://music-electronics-forum.com/attachments/11767d1290877369-mesa-20-20-poweramp.pdf (http://music-electronics-forum.com/attachments/11767d1290877369-mesa-20-20-poweramp.pdf)
Edcor offers some trans' that may work.
Would somebody please take a look which one may be closest in your opinion, also
concerning filament current and some advise on swapping it out with the old.
- I'm not so worried about it sticking out above the 1rack highth; it will be mounted in a rack)
- I'd prefer 240V input because I take it to Europe quite often and use a "step-up" here.
So here the list in the order of my preference:
1. http://www.edcorusa.com/p/746/xpwr144_120-240 (http://www.edcorusa.com/p/746/xpwr144_120-240) (200mA/3.5A)
2. http://www.edcorusa.com/p/889/xpwr047_240 (http://www.edcorusa.com/p/889/xpwr047_240) (120mA/2.5A)
3. http://www.edcorusa.com/p/644/xpwr051_120 (http://www.edcorusa.com/p/644/xpwr051_120) (125mA/4A)
Thanks and happy thanksgiving y'all, Stephan
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You are absolutely shure power T is burn ?
You are qualified to say that ?
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Thanks for the quick reply, Stratele52!
The PT is scorched, swollen and smells=certainly burned.
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Note that if the PT is blown, this may have been caused by some other circuit fault which is the real culprit. If so, a new PT might fry too. It's a good idea to test the circuitry with a bench poer supply or other PT temporarily; and monitor current draw for a quick shutdown if needed. Finaly, in case a circuit problem is intermittent, you might install fuses on the PT secondaries.
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Thanks for the quick reply, Stratele52!
The PT is scorched, swollen and smells=certainly burned.
+1000 jjasmill
You did not mentionned if amp is working with this transformer ? Or you just smell it and switch OFF ? Fuse burn ?
Test voltage at the PT output first. if voltage too low , disconnect PT from the circuit and test with no load.
Amp circuit / output tubes could be short
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> The amp is only 1rack unit high
That's 1.75 inches.
None of those will fit because they are all 3.22" the short way.
Electrically, only the XPWR144-120/240 is likely to carry four EL84.
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Thanks for the quick reply, Stratele52!
The PT is scorched, swollen and smells=certainly burned.
NO. this could mean , it is dirty OR it work hard ( short inside amp ? ) or because too small iron and not enough vent.
You did not answer to my question ; Is the amp is working or not ?
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And blown fuses can mean bad rectifier diodes,not necessarily bad PT.
Swollen? How? Out the sides? Bad smells:burnt diodes,fuses and resistors all smell pretty bad.
" I love the smell of napalm in the morning"
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Thank you PRR for looking at the shem and
helping me with the choice of a transformer.
Thanks everybody;
I see that I have to get it checked thru more
thoroughly and not just go with the first service-guy
I asked. The amp does not turn on,
blows fuse when mains switch flipped.
Thanks again all for helping me figuring out
what next step to take;
now I know that there is a transformer that
would work (I don't mind if it sticks out into the rack space above)
So much for now; I may poke into this thread again later
with an update.
Have a nice christmas season;
www.etarist.com (http://www.etarist.com)
> The amp is only 1rack unit high
That's 1.75 inches.
None of those will fit because they are all 3.22" the short way.
Electrically, only the XPWR144-120/240 is likely to carry four EL84.
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you might want to look at a marshall 20/20. they are also EL84 and 1 rack unit. those PT's are available on various websites. i don't know how close schematic and voltages are so check that.
here's a link with a modification and a schematic for the mesa: http://www.scribd.com/doc/6690230/Mesa-Mod (http://www.scribd.com/doc/6690230/Mesa-Mod)
on this schematic the PT part number is not clear but it is 561020. maybe you can get one from mesa.
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on this schematic the PT part number is not clear but it is 561020. maybe you can get one from mesa.
etarist write ; " Mesa Boogie wants $300.- plus shipping for the original.
That's an impossible number for me. "
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the marshall has a plate voltage of 410V (not indicated on the schematic, found this online, another source says 380V), the mesa 390V. i think this could work.
stratele52, there is more than one source for mesa transformers...
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stratele52, there is more than one source for mesa transformers...
+1
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WOW, thanks all for the kind and continuous advice.
Actually I have "plexi50" on it now; so the thread continues here:
http://www.el34world.com/Forum/index.php?topic=14719.0 (http://www.el34world.com/Forum/index.php?topic=14719.0)
Thanks plexi50; funny to now meet you here :-)
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The world and this transformer is getting smaller by the minute*
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;-)