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GK MBF 800 Issues...

Hi all,

I've had this amp for about a year and a half, and I love pretty much everything about it (when its operating properly). I've noticed a few issues recently and was wondering if anyone with any knowledge of these tube preamp hybrid amps could chime in:

1) The B channel (the dirty channel) no longer has any dirt...whatsoever. When I have the gain at max, there is no dirt present in the tone at all, and it is somewhat quieter than channel A, the clean channel. Could this indicate that the tubes need replacing, or a loose connection, etc?
2) I haven't noticed the fan kick on...ever. The amp doesn't seem to get too hot and I live in a relatively cool area, but I had read some people's complaints about fan noise and it seems suspicious that I've never even seen the fan turn on - even during a 3 hour gig. Does that sound about normal for these amps?

Thanks
 
This might be of some help:

upload_2017-11-17_17-35-40.png


Do you have Gain B turned up higher than Gain A?