I'm working on a friends amp, It is a raven rg 100, I think it might be the power transformer that is bad. It has very low voltage on the secondary. it has a 68v (ct) . there is five wires on the secondary two blue and a red then yellow then red.
I checked it plugged in and unplugged and the most ac voltage i got on it was 6.00 volts. I can't find a schematic anywhere.
I normally just work on tube amps so I was wanting to make sure It was the power transformer. I'll appreciate any help
Check continuity on the *Primary winding* first be fore worrying about the Secondary ones.
A high or fluctuating reading means the primary side is likely blown.
Some mains Transfomers have *one shot internal thremo fuse links* which renders tranny unuseable once they trip.
Don't forget the AC cord as well,, all the way from wall plug to internal connections.
I doubt a schematic would be of much help with this sort of problem.
Sorry I can't be of more help. Phil.
Quote from: phatt on October 14, 2009, 11:55:36 PM
Some mains Transfomers have *one shot internal thremo fuse links* which renders tranny unuseable once they trip.
Bummer, I hadn't ever heard of this. That would suck :'(
the transformer is reading 2.5 m ohms,it also says on the top of the transformer internal fuse 250/5a/130 degrees c.
The power cord was alright. If it is the transformer where is a good place to get a replacement. thanks
Excuse me, but what does:
Quote2.5 m ohms
mean?
2.5 (Meg)ohms or 2.5 (milli)ohms ?
Your internal fuse should be a bimetallic strip, opening at "x" degrees temperature as quoted, but closing again when cold , plus a regular fuse wire, 2x or 3x the regular current needed, which should never trip, provided the regular, external fuse has the rated value.
If somebody replaced it with a grossly over rated one, or "repaired" it with a piece of thick wire or crushed aluminum cigarette paper , yes, the internal one will open killing it for good.
Anyway, that's the "best" thing to happen, considering the alternative of bursting in flames and burning your house ; that's why UL (Underwriter's Labs) mandates such safety devices in every transformer .
A cheap chinese manufacturer would use only a short piece of thin wire.
Quote from: J M Fahey on October 16, 2009, 08:52:15 AM
Excuse me, but what does:
Quote2.5 m ohms
mean?
2.5 (Meg)ohms or 2.5 (milli)ohms ?
Your internal fuse should be a bimetallic strip, opening at "x" degrees temperature as quoted, but closing again when cold , plus a regular fuse wire, 2x or 3x the regular current needed, which should never trip, provided the regular, external fuse has the rated value.
If somebody replaced it with a grossly over rated one, or "repaired" it with a piece of thick wire or crushed aluminum cigarette paper , yes, the internal one will open killing it for good.
Anyway, that's the "best" thing to happen, considering the alternative of bursting in flames and burning your house ; that's why UL (Underwriter's Labs) mandates such safety devices in every transformer .
A cheap chinese manufacturer would use only a short piece of thin wire.
Very interesting stuff, learn something new every day.
The internal thermal fuses are not self resetting breakers. They are a component that looks sorta like a diode. or maybe a little cap. Typically they are wedged between the windings - you have to tear the transformer apart to get at it.
it reads 2.5 meg ohms,is there any place to get a replacement?I e-mailed raven amps with the part # and they never have responded.I hate to try to tear it open.
Yes, then unfortunately it is open.
Please draw a rough sketch of the secondary, the 5 wires baffle me. "Map" which one is connected to which one, and also what they connect to on the power PCB.
Logic says you should have a CT main secondary, maybe red/yellow(CT)/red or blue/yellow/blue.
Probably yellow is CT, red is 34+34V and blue perhaps 15+15V or thereabouts to power the preamp, but I'm only guessing.
One wire (yellow?) must go to ground, and the others to some diodes.
Once you know what you need, getting a *similar* replacement isn´t that difficult.
Probably the power amp is burnt too. Something fried that transformer.
Good luck.
Looking at the pictures and description of that amp on line, I think it's the successor model to the Rogue combo I scored for $40. The pictures sure imply what I found, and the power transformer nominal voltages look right.
You may be able to replace the transformer with *two* generic transformers; one a 68Vct 2-3A device for the power amp and one a 28? 30Vct? small toroid for the preamp, which is almost certainly a set of opamps. There was plenty of room in the chassis of the Rogue for trickery like this. I'm guessing there may be in that one.
A Really Good trick is to put in a 68Vct toroidal transformer for the main. Much lower hum emission.
Then very probably it is a generic amp, made by some Korean manufacturing giant, and sold in the US under any fancy name that that particular distributor likes.
Please post Raven and Rogue transformers pictures for side-by-side comparison, I also feel they may be the same.
In that case, the working one will provide voltage and pinout information for the dead one.
I believe you are right on the pinout, the two blue wires are 15 volts.Here is a picture of it. If I've attached it right. thanks for all the help.
OK, you can search for a 34+34 (or easier 32+32 or 30+30) V , 150VA toroid or conventional EI , such as the original one.
What will complicate things a bit is also getting the two 15V windings, although that´s not that unusual.
Google for it; if you don´t find it, I´ll suggest an option, although it´s not as straightforward.
Be ready to repair that power amp, *something* killed that transformer.
Anyway the whole stuff looks quite repairable, much more than the Line 6 posted elsewhere.
I can't seem to find what I need. is there any places you would suggest looking for one.I tried searching on google and found a few things but nothing with the 15+15. thanks.
Quote from: bvh123 on October 19, 2009, 10:06:20 PM
I can't seem to find what I need. is there any places you would suggest looking for one.I tried searching on google and found a few things but nothing with the 15+15. thanks.
I didn't think you would find a replacement with the 15V windings. That's why I posted:
QuoteYou may be able to replace the transformer with *two* generic transformers; one a 68Vct 2-3A device for the power amp and one a 28? 30Vct? small toroid for the preamp, which is almost certainly a set of opamps. There was plenty of room in the chassis of the Rogue for trickery like this. I'm guessing there may be in that one.
You could put in this one for instance:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1326-ND (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1326-ND)
and bolt it right to the bottom of the chassis. You parallel the primaries with the existing transformer primary, and connect the secondaries where the old transformer's 15v/15v secondaries went. It's another $20, but it's better than junking the amp, right?
Notice that you're contemplating doing things that require messing with rewiring AC power line circuitry. This is major dangerous to yourself and others if you don't already know what you're doing and how to do it safely. Do not try this if you don't already know how to do it right. It's not worth dying for - or having someone else die because you didn't understand something.
Transformers like this won;t be in Mouser so much, but i bet you can find a pretty similar existing amp in one of the large lines like Peavey or Fender or Crate, and use the power transformer from that.
thanks for all the help on this,I decided to take the transformer apart and check the fuse. the fuse was bad. It looked more like a cheap diode or something.but I wired it back up and turned up slowly with a variac. I checked voltages and and everything seemed to be alright.So i played through the amp for about an hour and it seemed to work well. I guess it might have been a bad fuse,but I'm going to keep checking it for a while. because most of the time a fuse blowing mess means something else is messed up,but maybe I'll be lucky. thanks for all the info guys I appreciate it very much.
Great news !!
In fact, I wrote a post for you suggesting to take a box-cutter and carefully slit the insulating transformer paper , layer by layer, until you found it (it should cause a "bump" in the paper), but decided against sending it, for safety and liability issues.
But you did it on your own and were lucky, good!
It was a plain fuse, so it could be anywhere,it happened to be close to the surface; if it had been a true thermal one, the best place would be *between* the primary and secondary windings, fully surrounded by copper, completely inaccessible.
Enjoy your amp, you deserve it.
I find that the thermal fuses are indeed packed between windings, but they are also accessible if you dig through the paper. Those silver diode looking things are thermal fuses, not common fuses. You can wire past them and take your chances with safety. You can buy new thermal fuses from a variety of suppliers like Mouser or MCM. Look for Thermal Cutoff.
They are tucked in the edge of the windings rather than square in the middle.
Good to hear you got it all worked out, another win for the DIYer!