Variac on zero, power switch off- connect power cord. 2). Connect either output to load box (load A). 3). Resistance loads open (switch in. Gallien Krueger rb Schematic Diagram. Uploaded by esquisof. Gallien Krueger rb Schematic Diagram. Copyright: © All Rights Reserved. Download as. Hello, Service Manual of the Gallien Krueger rb this is a amp for bass, there are layout, pcs, schematics for preamp and poweramp.

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Started by Ilya The Lab. Started by skipwave The Lab. Started by Ghengis The Lab. Started by 3nity Drawing Board.

Good morning, for sentimental reasons I picked up a Gallien Krueger B, it’s an earlier version of the popular RB but it’s all discreet along the lines of an old Sunn or Acoustic. Also, it’s generally not as loud as it should be. I’ve gotten pretty good with 4000rb but I don’t know anything about transistors so looking at the schematic and the circuit board it’s not adding up to me.

Here’s what I’ve done so far So first question, are these compatible? I’ve been looking over the data sheets, and seems close, but another set of eyes that’s familiar with transistor specs would be greatly appreciated.

Let me know what else I can do to help you guys help me. Despite not knowing much about transistors I’m pretty sure they’re supposed to be soldered to the circuit board.

One of the replacement transistors was mounted but never soldered, next to it was a fried resistor. Fixed that up, things are pretty good now, but it still won’t bias right. I don’t have much faith in the work that was done to it before I got it. Can’t see what you done from miles away. What’s wrong with the bias? Votes for the wrong politicians?

Help repairing Gallien Krueger B

February 19, I believe the bias never worked as intended. More will cook, today or next summer.

CJ Member California Posts: If I can’t fix it, I can fix it so nobody else can! If your wondering about the NTE parts use their online cross reference http: You tell me whar a man gits his corn pone, en I’ll tell you what his ‘pinions is.


Per the tech note on the schematic measured across Q13E and Q14E, adjusting R49 did very little, 9mv is about the highest it will go, 7mv the lowest.

But will be a little rough-throat sounding around the 1W level. The obvious solution is: You didn’t drag a hundred pounds to under-whelm the bar’s ventilation rumble. That bias circuit reads wrong to me. Can someone check me? There’s a transistor, the trim-pot, two 1K resistors, and two more resistors. If this ohm resistance is to make significant change in bias, it must be a fairly large part of the total resistance divider.

Assume the total is 1K to 2K. Q4 Q5 flow about 4mA 0. We need about six times 0. A ohm resistor would be “right”, except it has an all-wrong temperature coefficient.

Q9 is a small Darlington with gain over 2, If it actually takes most of 4mA, the base current is less than 2uA. The resistance divider current must be “much” higher. I think the divider values are about 50 times too small. The bias voltage is dominated by Q4 Q5 current, which increases with temp, instead of a multiple of Q9 voltage, which decreases with temperature. For a fairly constant idle current in Q13 Q14, we need a bias that DEcreases when the amp gets hot.

If this does not happen, the amp gets hot, idles at higher temp, gets hotter yet, and goes into “run-away”. I’d want to do it different. When things go wrong, it gets VERY expensive fast. In the old days I had and 10 ohm resistors at 10 or 20 Watts. I’d put these in series with the power rails.

Gallien-Krueger 400RB Service Manual

For a correct bias, the drop in the resistors was small. When things went wrong, the voltage would fall very fast, the resistors get hot instead of the transistors. However in a W amp you need W resistors to handle disaster gracefully. For a kruegee, I’d go crude. However if connected wrong, the amp will burn-up at turn-on. You need some mildly ga,lien lessons before you try this on a W, especially a “beloved classic”.

Pucho, thanks for the tip on the NTE stuff, I had no idea that existed. CJ, thanks for the context regarding the topology. Since I really like how the preamp sounds I’ve been thinking about ditching the power amp and installing something else. Maybe one of these hypex class D modules. In the mean time I’ll have to read that a few more times.


The resistor-string is now Ass-uming that ,rueger is exactly 1. Ass-uming that the output two triple-Darlingtons needs six times 0. Different transistors have different areas galpien doping so the exact voltage needed will vary.

You are unable to reach 0.

It sure looks like you should have plenty. This makes me wonder if one of the other parts is still sick. Each transistor base-emitter drop should be near 0.

PNP will tend to be 0. A great difference, say between Q8 and Q10, is suspicious. The output transistors are double-stacked so each gets less voltage. The bases of the outer devices are nominally half the supply voltage, noted as The 2nd one is the right one. The schematics I got have several versions of the power amp. I’ll sit down this weekend and measure about, that’s really helpful info PRR. Since my last post I’ve been enjoying this amp, the output was a little hairy at power up but I’m using it in a punk band.

Opening it up R50 had burnt up.

Here’s a list of what I’ve done and what the results were thus far It’s a little hard to identify which resistor it is since at this point that area of the pcb is fairly blackened.

Any insights would be appreciated. I’ll keep replacing resistors but if anyone could help me figure out a way to keep it powered on long enough to measure some voltages that’d be a big help. I’ve attached a screen shot of the schematic problem area. My version of the power amp is page 7. Gallien-Krueger RB, got schemo, need help fixing. Soundcraft b schematic Started by Ghengis The Lab.

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