Gallien Krueger 200RG Amp - Will not start up

[TomCarlos]

MEF Members -

I hope to rescue a Gallien Krueger 200RG (G&K) Amp that is reported to "not start up." Before I power this amp up, I need to clean up some connections (incoming power lines, ground, etc) and replace the main fuse holder. While doing all this, I also want to look around for other obvious signs of distress.

This amp uses the 60039C PC board (Power Supply, Output). The only schematic I could find was for the "B" version. So I am hoping that is close enough to help me troubleshoot.

In the Power Supply section, for the (+15) and (-15) supplies, I do not see any fuses for F1 and F2. I noticed that a handful of transistors have the collector lead cut. That connection is made through the mounting screw to a trace on the bottom side of the PC board.

The five 470uf Caps were unsoldered from the board. I did measure them and seem appear to be ok.

The other odd ball thing is the Bridge Rectifier. I have never seen anything like this. It is odd how the leads are wires that go through holes to connect to the PC board. I am inclined to pull that thing and test it. But first, I will solder the filter caps back in and use a bulb limiter to see if I get anything.

I've looked for other threads on this amp (or the bass amp equivalent). But I cannot find anything specific to the "C" version. Anyone have notes on this amp? I am curious to know if G&K removed the F1 and F2 fuses or if they are buried as part of the transistors.

Thanks, Tom

[g1]

They used that package bridge a fair bit. KBPC102 is 3A, 200V. You can get KBPC108 from mouser I think, 800V but should be same size. Or you can use the kind with lugs and run wires. Best to keep it flat to the heatsink like that package though, rather than the upright style.
Probably didn't use the fuses in this version, some of them did use low value resistors to act as fuses for the LV supplies.

And since someone's already been in there, make sure it has the proper insulator bushings so those transistor screws don't contact the heatsink.

[TomCarlos]

Thanks G1 -

Yes, I will give this a careful look over before I attempt to power up. The explanation of "Will not start up" could also mean that the amp keeps blowing fuses. I'll report back.

[TomCarlos]

Ok... update....

After some initial cleanup and installing a new fuse holder, the amp is working.... but....

I still need to replace the 470uf filter caps. The bottom side of the board had barely any lead from the caps coming through on a couple. So I temporarily added some wire to make sure the caps are connected.

For the high supplies, I am getting (+) and (-) 55.5 volts.

On the low supplies, I am measuring (+) 13.9 volts and (-) 14.5 volts.

I am measuring -55.5mv dc at the output (with an 8 ohm load applied - for good measure).

If this "C" version of the PC board works like the "B" version (as shown on the schematic), there is a 1K trim pot (R15). Oh is that pot sensitive!! And if this board is like the "B" board, I identified the .33 ohm resistors as follows:

Left to Right - R24, R26, R27, R28, R21.

As per the schematic, I am able to adjust the Trim pot to get close to 10mv across R21 and R24. But I cannot get 0v (to ground) where they meet (as shown on the schematic). In fact, I am measuring approx -63mv. That is why I am seeing -55mv at the output.

I am out of the 470uf caps - they have been ordered. So once I replace those, I will see where this amp stands. For good measure, I did replace the other electrolytic caps on this board.

And... does anyone know why Channel B has TWO volume controls plus a Master Volume? What's up with that?

[g1]

I think you could select vol.1 or 2 with footswitch? So like a footswitchable boost?
Also, I think they often did a funny thing where R21+R24 meant the 2 in series, so 10mV total from Q4 emitter to Q8 emitter?
Schematic shows +/-30mV at output, but you are not far off. It may change if you were setting at 10mV for each resistor.

[TomCarlos]

G1: I interpret the note the same way you did - 10mv from Q4 emitter to Q8 emitter. But that does not get me to 0v at the juncture. I will continue looking at this.

For those visiting this thread - looking at the pc board vs schematic (B version), the version "C" board is different when it comes to the transistors around the trim pot (Q5, Q6). On the board, I see the Emitter of the PNP (MPSA056) connected to the Emitter of an NPN (MPSA06). For now, the transistors are turned on.

As for the footswitch, it switches between A and B. There is no boost. So I will shrug my shoulders over this one.

[TomCarlos]

I found something on the 2 Volume controls on Channel B. The amp has a "two-stage gain section to shape the OD, they interact with each other depending on settings to give you differing levels of overdrive." So after adjusting the two volume controls (thinking of them as two different "Pre" levels), you then have a single Master Volume (kind of like a post?) for Channel B only.

I was able to get to the back side of the Preamp Board - 60036B.

I just fired off a second email to G&K in the hope of getting these two schematics. If so, I will post them here for others to have.

[TomCarlos]

Gallien Krueger 60039B Preamp Schematic for 200RG Amp

Our friends at Gallien Krueger sent me a schematic for the 60039B Preamp board - thank you G&K.

Unfortunately, they cannot locate the schematic for the "C" version of the 60039 Power amp board - but I will keep searching!!

For those who collect schematics - see attached!!

Tom