Bass Fumbler Posted February 13, 2018 Share Posted February 13, 2018 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. Quote Link to comment Share on other sites More sharing options...
ern500evo Posted February 14, 2018 Share Posted February 14, 2018 I would imagine if it was the valves, that plugging into the fx return would eliminate the the problem, as by doing that you’re basically bypassing the preamp? Quote Link to comment Share on other sites More sharing options...
discreet Posted February 14, 2018 Share Posted February 14, 2018 (edited) 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 February 14, 2018 by discreet Quote Link to comment Share on other sites More sharing options...
deepbass5 Posted February 14, 2018 Share Posted February 14, 2018 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 take off the top cover and have a look and decide if you are up for it. Quote Link to comment Share on other sites More sharing options...
Bass Fumbler Posted February 14, 2018 Author Share Posted February 14, 2018 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. Quote Link to comment Share on other sites More sharing options...
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