v4b head issue

I just purchased a new Ampeg V4B RI with a 212av cab from guitar center. Love the all tube tone, however, at certain frequencies (when i play a G# or A on the A string or E string), something inside the V4B was rattling. Took it back to GC and they got me a replacement unit. Unfortunately, with...

I have a Linden, NJ version Ampeg V4B head that is not working properly. The output ranges from nothing to very weak to almost normal volume, depending on whether the Ultra Low rocker switch is positioned "just so". Very touchy, seems like this rocker (possibly the Ultra Hi and 3-position freq...