GK Amp Combo

[Radiotech1964]

Just got an MB150E in with what seems at first glance to be a muted output. I have the 150S manual but not the 150E Is there noticeable difference between the two models? Looks like this one has had some previous work in the power supply section. I saw a couple of hard wired paths and some PCB burn. Nothing major though LOL!

Thanks in advance!

Wt

[J M Fahey]

The amps themselves are basically the same, just the power supply is different ... even so both supply same voltages to the rest of the amplifier.

So the circuit you found should be close enough for power amp troubleshooting.

Just from memory , I think it had dual secondaries, one supplying around +/-42 or 45V DC for the power amp, another raw +/- 24 or 27V DCV which were later regulated down to +/-15V for preamp duty.

But nothing too weird.

[vintagekiki]

https://www.manualslib.com/manual/1036729/Gallien-Krueger-Mb150s.html#product-Microbass%20MB150E

https://www.manualslib.com/manual/1036729/Gallien-Krueger-Mb150s.html

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/SM_scena/Gallien-krueger/

https://elektrotanya.com/showresult?what=GALLIEN-KRUEGER

http://schems.com/bmampscom/gallien/

[g1]

That 3rd link above from vintagekiki is the only one with both halves of the MB150E service manual. It's big.
http://bee.mif.pg.gda.pl/ciasteczkow...ice_Manual.pdf (vol.1)
http://bee.mif.pg.gda.pl/ciasteczkow...ice_Manual.pdf (vol.2)

[g1]

The amps themselves are basically the same, just the power supply is different ... even so both supply same voltages to the rest of the amplifier.

I know there was a model that had both a switching and linear supply version, not sure if it was this one?
In this case, the "S" is the standard preamp, and the "E" is the stereo chorus version.

[Enzo]

I don't recall the alphabet soup, but they had a little amp with a switching supply. I got pretty good fixing them. Then they stopped supporting the switchmode supply and offered an update kit. A transformer and linear board to mount in the amp. $$$

As I recall, there was a square hole in the board, and transistors mounted around the hole so they could be screwed to the heat sink revealed by the hole. Due to flexing and vibration, the transistor legs tended to snap off the transistor bodies. ALso a couple TO220 rectifiers, same issue.

[Radiotech1964]

I think this one has the linear power supply vs switch mode. It's had some previous work around Q513,looks like a burned trace once upon a time. Haven't dug into that yet as first glance looks ok.

Thanks, everybody for the quick replies and information! Also, I'm sure the 150S diagram exists here but if anyone could use it let me know and I'll be happy to upload the file.

Thanks again!

WT

[g1]

Sure, upload it if it's different than what is in post #4. The more service info the better!

[Radiotech1964]

GK Schematics

Sure, upload it if it's different than what is in post #4. The more service info the better!

Couldn't agree more!

Here it comes..