Help identifying bridge rectifier values/ratings.

[mtyes]

 Hi,
I need to replace a bad bridge rectifier in my Sovtek Mig 50. I've removed the old one but the only markings seem to be manufactures markings as opposed to values.  It reads KU403A (403 amps?) followed by 9205.

 Here is a link to the schematic but it does not list the value. http://www.blueguitar.org/new/schem/sovtek/mig-50.pdf

 I could make my own if I know what value diodes to use. Here is a picture of a DIY BR in the same amp.http://franck.davot.free.fr/mig50/mig50-xl3.jpg Can anyone identify the values? It looks like a single grey or silver band but I'm not sure.

 Any help would be appreciated.


Donny

[sluckey]

I would use four each 1N5408.

[mtyes]

I would use four each 1N5408.

Thanks Slukey. Any idea if Radioshack will stock these?

[sluckey]

Go to the website and check

[DummyLoad]

http://www.mouser.com/ProductDetail/Vishay-Semiconductors/VS-GBPC3512W/?qs=sGAEpiMZZMtQ8nqTKtFS%2fP%252blm5IsPhsjHE2xmGq72UQ%3d

[DummyLoad]

I would use four each 1N5408.

Thanks Slukey. Any idea if Radioshack will stock these?

http://www.radioshack.com/product/index.jsp?productId=2062575   closest thing they stock in stores that may work - you'll need 2 packs @ 2.50/pack pretty steep for just 4 diodes that are 11 cents each bulk. still though, 1.5A part likely won't survive for long.
 
do you have a fry's nearby? they may have the 1N5408 replacement in NTE brand. part number is NTE5809. also pricey...

it would be best to use a 3A or better part - the original bridge was likely a 4A bridge.   

--pete

[mtyes]

Go to the website and check

The reason I didn't do that is because the online store has nothing to do with my local store and I hoped to pick it up locally.I was asking general question because sometimes people will say, don't bother checking radio shack, you're not going to find it there  etc.

I might end up making my own using 1N5408s if I can't find something that will work.

I'm still unclear about exactly what amp and voltage to look for. Dummyload suggested a BR that is 3A and over 1000 volts.  Pete suggested the original is probably a 4amp bridge.   Does that mean anything above say a 3 amps and 1000 volts will work? Can I use say a 6A 1200 volt?

Thanks to everyone for all the help.

[sluckey]

The 1N5408 is rated for 1000V_piv and 3A. Since the bridge uses diodes in pairs, it would effectively be rated at 2000V_piv and 3A.

eBay is a good cheap source for 1N5408

[mtyes]

Ok,
 Thanks again.

[SILVERGUN]

Does that mean anything above say a 3 amps and 1000 volts will work? Can I use say a 6A 1200 volt?

Yes...would work....but will it fit?
The one that DummyLoad posted is a great replacement for that bridge because you get a lot of rectifier in a little package that will closely fit your board (you'll just have to bend the pins a little)...and it's in stock...the stock Sovtek BR should be approx 22mm (square), with pin spacing at about (15mm square).........those vishay's are 28mm square, with 17mm pin spacing

pete and Dummyload are the same guy.......he knows stuff we don't.....he came up with that part# sooo fast that you might have thought there was no thought put into it.....that is not the case

[mtyes]

Does that mean anything above say a 3 amps and 1000 volts will work? Can I use say a 6A 1200 volt?

Yes...would work..

Thanks.

..but will it fit?

Not without a little bending.

The one that DummyLoad posted is a great replacement for that bridge because you get a lot of rectifier in a little package that will closely fit your board (you'll just have to bend the pins a little)...and it's in stock...the stock Sovtek BR should be approx 22mm (square), with pin spacing at about (15mm square).........those vishay's are 28mm square, with 17mm pin spacing

The Vishay actually looks smaller to what I have in front of me but I haven't measured it.

pete and Dummyload are the same guy.

I knew that.

[sluckey]

I don't see any parallel diodes in any of the soundcity schematics on this site. Can you post or link to a schematic that has parallel diodes in the bridge?

[mtyes]

Just a quick update.

 I removed the bridge rectifier and tested it out of the circuit and it tests bad. Also the PT makes no noise with the BR removed so I think we found the culprit. I found ten diodes (1N5408) for $1.00 shipped on ebay so I'll update later in the week.

Thanks a lot for all the help guys!

I also happened to find a brand new muffler for my Honda Helix for an unbelievable price.  The OEM Honda muffler is almost $400. The Chinese knockoff is about $150.. I found the Chinese version for $29 plus $13 shipping.  I love ebay!!

[HotBluePlates]

For future repairs like this, you may want to look up the amp repairman at your local music store.

They'd likely have small things like diodes on hand, so you don't have to waste money on shipping for just a few. When I've bugged repairmen for small, light things like this (say, bone nut/saddle blanks) they've sold me what they had on hand at a good price.

[sluckey]

I do not have a link, and understand your frustration.

Not frustrated. Just disappointed. Oh well...

[mtyes]

Here is my promised update!

I ordered the diodes (In5408) on ebay and it's been 3 weeks and I haven't received them so I went down to Radio shack and found some similar diodes but 3amp/600 volts instead of 3A/1000. So that's 1200 volts total which should be fine, correct?

  The diodes were harder to manipulate than I thought. The wire/leads were thicker than I thought and after knotting them together I could not get the wire hot enough to solder. I ended up just twisting them together with a pliers which actually worked very well creating a tight connection.  After soldering the new part into the CB, I plugged it in and its working!

I want to thank you guys for helping me out!! The amp would have sat ( like my Traynor Bassmate has been for 6 months now) for the next year if it weren't for your help.

 I have just two more questions. Before I put it back together I want to install the missing bright caps  (both volumes) .
 
*What's the minimum voltage I should use?
*Since both bright caps have been removed by someone before I acquired the amp. Why is the number 2 input brighter than the number 1 input? It's a single channel amp. Shouldn't they sound the same without a bright cap on the one of the volumes?

[Willabe]

You still have to solder them together. After time those leads will corrode and will lose their connection to each other.

I went down to Radio shack and found some similar diodes but 3amp/600 volts instead of 3A/1000. So that's 1200 volts total which should be fine, correct?

Maybe not for long life.

Your amps B+ ~500dcv? You need at least 2x 500dcv and 3xdcv will be safer. Higher than normal AC wall voltage and/or AC wall voltage spikes can eat up the head room you have.  


              Brad    

[mtyes]

You still have to solder them together. After time those leads will corrode and will lose their connection to each other.


              Brad     

 Once I get a bigger soldering Iron I'll finish it off properly.

[HotBluePlates]

... Before I put it back together I want to install the missing bright caps  (both volumes) .

The schematic you linked shows no bright caps on either volume. I do, however, see a 470pF cap across channel 2's 300kΩ mixing resistor.

*What's the minimum voltage I should use?

*If* you had to replace that 470pF cap, it doesn't have a critical voltage rating as supply voltage is already blocked by the coupling caps.

That said, a value like 470pF is likely to be a ceramic or mica cap; even one of these rated @ 500v is pretty small. You'd probably pick the 500v cap just because the lower-voltage caps are too small for big clumsy fingers.

Why is the number 2 input brighter than the number 1 input? It's a single channel amp. Shouldn't they sound the same without a bright cap on the one of the volumes?

So again looking at the schematic you posted in your first post, this would be called a "2-channel amp" if this were the 50's. Yeah, they share a common set of tone controls, but each input jack has its own triode voiced differently.

Looks like channel 1 has a 220uF cathode bypass cap, while channel 2 has a 0.68uF bypass cap. That would make channel 1 muddy and channel 2 bright. The 470pF cap bypassing channel 2's 300kΩ mix resistor brightens things further, without extra bright caps on the volumes.

And are you sure there are supposed to be bright caps? The schematic doesn't show any. And I'd think for a balanced sound you'd still need to jumper the input jacks so you play through both channels at once (at least, that's what I had to do with my old '73 50w Marshall head).

[mtyes]

The schematic you linked shows no bright caps on either volume.

 Yes, you are correct about the schematic but we pretty much concluded (in another thread) that the two caps, which have been sniped off on my amp, located in close proximity to each volume control on the circuit board must be bright caps. I've owned three of these amps and this one seems darker than the others so it would make perfect sense if these missing caps are bright caps.

*If* you had to replace that 470pF cap, it doesn't have a critical voltage rating as supply voltage is already blocked by the coupling caps.

That said, a value like 470pF is likely to be a ceramic or mica cap; even one of these rated @ 500v is pretty small. You'd probably pick the 500v cap just because the lower-voltage caps are too small for big clumsy fingers.

But radio shack does'nt have higher voltage caps and I'm inpatient. So I could use almost any voltage, no matter how low?

So again looking at the schematic you posted in your first post, this would be called a "2-channel amp" if this were the 50's. Yeah, they share a common set of tone controls, but each input jack has its own triode voiced differently.

Looks like channel 1 has a 220uF cathode bypass cap, while channel 2 has a 0.68uF bypass cap. That would make channel 1 muddy and channel 2 bright. The 470pF cap bypassing channel 2's 300kΩ mix resistor brightens things further, without extra bright caps on the volumes.

Thanks for that!

And are you sure there are supposed to be bright caps? The schematic doesn't show any.

Am I Certain? Not at all but it seems reasonable that the caps located near the volumes that have been snipped on my amp are bright caps.. That was the general consensus in a different thread I started anyway. Would else would they be?   If you do an image search of a Mig 50 chassis, you will see that some of them have the caps and some seemed to have had them at one point and they were clipped. I assume this was a popular mod at some point. Either that or I'm really way off and they are not bright caps.

And I'd think for a balanced sound you'd still need to jumper the input jacks so you play through both channels at once

Yes, That's what I do.. but I still want it brighter.. I use the amp for recording and I keep the bass all the way off and presence all the way up and I would still like it to be brighter... more like my 63 blond Bassman was.  The sovtek still sounds great the way it is.. I love these amps , hence the reason I've owned three.. but this one could use a little boast in the highs.

[HotBluePlates]

... we pretty much concluded (in another thread) that the two caps ... must be bright caps. I've owned three of these amps and this one seems darker than the others ...

I see!

... But radio shack does'nt have higher voltage caps and I'm inpatient. So I could use almost any voltage, no matter how low? ...

Yes, as long as the coupling caps at the plates of the first stages don't fail.

Be careful about being impatient with electronics.  But I understand...

And I'd think for a balanced sound you'd still need to jumper the input jacks so you play through both channels at once

Yes, That's what I do.. but I still want it brighter.. I use the amp for recording and I keep the bass all the way off and presence all the way up and I would still like it to be brighter...

Since the Mig 50 is copping a Marshall every other way, why not make the 0.022uF coupling cap smaller in the channel that has the 0.68uF cathode bypass cap. Marshall did all the other brightening tricks in the Mig 50, but also made the coupling cap smaller so it would strip out more bass.

[mtyes]

Since the Mig 50 is copping a Marshall every other way, why not make the 0.022uF coupling cap smaller in the channel that has the 0.68uF cathode bypass cap. Marshall did all the other brightening tricks in the Mig 50, but also made the coupling cap smaller so it would strip out more bass.

Now that you gave me a reason to order more than a single cap, maybe I'll place an order for a few different values and experiment.
Indecently, the original diodes that I ordered over three weeks ago to build the BR came in today, one day after I gave up on them and made a trip to radio shack.  I did notice that the higher 1000 voltage caps I received are actually smaller than the 600 volts I bought at radioshack. Is this normal?