MKV EQ switching issue - please help

[welshboogie]

Hi Guys,

Just picked up a used MKV and it looks like it has a switching issue with the EQ.

Regardless of where the EQ is set on the front panel it stays engaged - the lights come on/off as normal when in whichever mode (and even in FS mode) however the EQ remains engaged - you can even hear it clicking in when you engage FS/switch.

The Preset/Slider works fine - its just the amp will not switch out the EQ whatever I try..

Also noticed that wen switching between wattages that the reverb almost mutes for a few ms until a note is played.

Could this all be linked to a bad tube somewhere - is that worth a try? or is this more a switching matrix issue that needs a tech?

 

[jaslan]

If you unplug the foot switch, do the switches on the front panel work correctly?
It might help narrow down the problem to the foot switch, cable, or switches on the panel.

 

[welshboogie]

Happens with footswitch unplugged too..

I suspect a JFET gone down looking at earlier posts on here.

 

[jdgebha]

I actually had something similar and it turned out to be the rectifier tube. Not sure why but I replaced it and all my eq switch issues went away.

 

[mace]

I'd bet on the JFET being bad.

But, the reverb comment you make I seem to think that is somewhat normal. The reverb cuts out a bit when switching. I think this is by design and a byproduct to minimize popping and such.

 

[welshboogie]

Yep!!!

Amp just back from tech - replaced JFET’s on the Graphic and all good, I’m sure the EQ was half in previously as it sounds completely different now - it was all honky and nasally (almost out of phase sounding) previously - it now sounds like a Mark Series should sound like!!