Thunder 1 Twin - Volume (Push/Pull Knob) Issue

I bought a Guild Thunder 1 Twin on ebay. The volume knob is push/pull, when pulled you get a brighter sound. There is a HUGE difference between the regular setting, and the bright setting (when pulling the knob). The bright is as advertised, but when playing it normal (with the knob at it's regular setting), the amp is muddy. I haven't had the amp serviced or checked out since I've owned it. Is this how the amp sounds, or do I have an issue? The reason why I'm curious is because when on the bright setting the amp sounds amazing, just a bit bright.. I know this is an old amp from the mid 60s, and it's probably due for a servicing, but before I bring it in, I just want to know if the amp is supposed to sound the way I described, with such a drastic sound change when pulling the volume knob, or if it's not supposed to be like I described.

Thanks,
-Adam

Hi Adam; no, the amp shouldn't sound muddy. The lucky answer would be that the 'normal' switch contacts are dirty but the 'bright' contacts are clean. Had a chance to try cleaning the switch? You'll need CAIG deoxit / lubricating-type cleaner. Bath the switch body, pull/push switch over and over, replace chassis and see what happens.

While you have the chassis out, you might as well clean the pots and tube sockets ... you'll have the spray cleaner already in your hands. If it isn't the switch, well ... it's something else but whatever it is, a good tech can find the problem for you. Good luck! CJ