Galien Krueger 250ML

[Perkinsman]

I was given this amp by a friend along with a small baggie containing several components that had been pulled from it. I opened it up and immediately noticed a burn mark on the back wall. I replaced the components in the baggie with new parts and powered up on variac. After 35v, one of the transistors near where the burn mark started slightly smoking so I shut down. I have a pdf schematic but I'm unable to post it here for some reason. Does anyone have a good schematic for this amp they can post here? I could use some help and not sure what to do next.

[The Dude]

Here's the schematic I have. A picture of the burnt area would help.

[Enzo]

Let us talk of the variac first. You absolutely need to monitor mains current while using a variac. Turning it up until a part smokes is using it wrong.

What you do is watch mains current draw, and start turning up the variac. If you see current start to rise with the voltage, STOP RIGHT THERE and turn it off. That should happen before things start to get hot. It doesn't mater if that happens at 35v or at 65v. WHat matters is a rise in current means there is trouble.

[Perkinsman]

Thanks for posting the schematic. I did notice that the current meter start to rise as I was slowly increasing voltage but it happened very quickly. The wisp of smoke came from Q34, in front of the scorch mark next to Q35 on the back wall. I've cleaned it up but you can still see the shadow it left. Btw, I had also installed that mylar cap initially because someone had put a resistor in that position.

Also, what is the significance of R164 & 164a? Why is one called "a"? 164a was charred so I replaced it as well.

[Enzo]

Any burnt resistor means something else is shorted, likely a transistor.

ANy chance that resistor you replaced with mylar was green? Small ceramic caps look like resistors.


Have you any idea how hard it is to find "R164" in a sea of parts like this. I finally did, but really, tell us where a part is in a circuit next time.

R164 is the base resistor for the pair of transistors regulating the +15v supply. Note R163 and 163a also exist on the -15v circuit. AT some point they saw the need for a current limiting resistor feeding that regulator, so they added the 10 ohm part. Instead of finding the last resistor number in the whole drawing they just made it R164A.

So Q34 and Q35 were bad, and you replaced them, right? And that would explain a burnt R164a. And remember that mystery resistor? Look in the schematic and find C63 right between those two transistors. I could be wrong, but I suspect that is what you replaced. Did that resistor you pulled have red-red-red stripes?

[Jazz P Bass]

Maybe it's the pic but I do not see any isolating mylar pads behind Q34 & Q35..
Aside: I have worked on a number of these beasts and I somehow failed to catch this little ditty in the Test info.
'Tap brain on bench'.
Cute.

[Enzo]

I don't know if that was meant in fun or if someone was Canadian. When we played in Canada, it was hard to get used to, all the guys there called amp heads a "brain". So it could have meant, tap the amp on the bench to see if anything was loose.

[g1]

That's a new one for me, but makes sense as far as the context of the service notes goes.

[Perkinsman]

I replaced Q35 but not Q34. I’ll have to order that. I replaced the charred 164a with 100k. NOT SURE what the correct value for 164a is, can’t find 164a on the parts list, I just went with what I could read off the charred one but it may be way off. R164 is supposed to be 22k but it read 11 ohm so I replaced it.
The mystery resistor (yes, it was red/red/red) is what I replaced with the green Mylar cap. Here’s a pic of what I removed:

[Enzo]

Dude posted the schematic, look at it. R164 is in the power supply. R164a is 10 ohms

I suspect you may have R164 and R164a reversed, as the 11 ohm thing is close to R164a value, and R164 should be 22k. Both of them connect to the same point at one end.

Note the green color of the C63 "resistor" unlike the tan bodies of the others. That is a ceramic cap.


I guess I can't speak for all of Canada, but in the part of Ontario down towards Windsor, that was the case.

[The Dude]

Maybe it's the pic but I do not see any isolating mylar pads behind Q34 & Q35.......

^^^^^^THAT!

[Perkinsman]

This is the way I found the amp, none of the transistors on the wall had pads, so I assumed that they didn’t use them. I cleaned the old paste off & put new paste on. I can put pads on if necessary but Q34 isn’t against the wall, I think you meant 33&35. Q34 was the little one that smoked & is the standalone in front of Q35.

I think the 164 &164a resistors were installed backwards.

What is the uf value of C63? I’ve never seen those type caps, how is the value read? .22, .02, .002, etc?

[g1]

I suspect you may have R164 and R164a reversed, as the 11 ohm thing is close to R164a value, and R164 should be 22k. Both of them connect to the same point at one end.

If this is the same layout, R164A (the 10ohm) should be closest to the edge of the board.

[Enzo]

Value is read just like resistors but in picofarads instead. So 2200pf or 0.0022uf

PArts list bottom of page 17


Aha, simulpost.

That looks like the right layout.

[Perkinsman]

Yes, same layout & I’ve got both resistors in, put C63 back in & placed new pads behind Q33&35. I still need to replace Q34.