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GK MB500 Fusion Problem


Bass Fumbler
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My GK MB500 Fusion has developed a problem.

When it is switched on, the volume is low and the sound is scrunchy/crackly, this is the same on both the A and B channels and makes no difference if it is used with speakers or headphone only.

I have tried using a 1/4" jack into the send & return sockets on the effects loop, with no change in sound.

I was wondering if it is maybe the valves.

Does anyone have any ideas?

Also does anyone know a good amp repairer in the Harrogate/ Leeds/ York area?

Thanks in advance.

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My guess is that it's one of the input (preamp) valves saying goodbye. I'd usually suggest replacing it yourself, but I know that there are some very high voltages involved in these amps, so I'd recommend Pro Audio Service or somewhere like that. Is it still under warranty?

Edited by discreet
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sounds like a valve to me too, I have changed all of mine when i had one of these for NOS British valves, It does require removing a head sink or trany as i remember at the back of the valves they all sit in their little metal shielding sprung jackets but there is not enough room to pull them out and bend them up and away without bending pins or worse. If that doesn't phase you it is only 4 screws. you can then lift all three out fixed together then removal of each valve is easy. With the power off :D take off the top cover and have a look and decide if you are up for it. 

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I suspect it is something to do with the valves. I’ve just playing through it & it sounds normal again!

i did take the cover off the other day, and I decided I wasn’t going to risk taking the valves out, as you say, they are in a very restricted space. 

My local music shop does repairs, so I think I’ll just take in and let them sort it out.

Thanks for your replies.

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