User Manual

V-4B Bass Guitar Amplifier
13
Changing the Tubes
Tubes wear out in direct proportion to how often and how hard you use the amplifier. Power tubes
shouldbecheckedatleastonceayear–morefrequentlyifyouusetheamplifiernearlyeveryday.
When power tubes wear out, the amplifier will begin to grow weak, lack punch, fade up and down, or
lose highs and lows. Power tubes work together in a push/pull configuration and should be replaced
at the same time with matched or balanced tubes. Your dealer can recommend the best replacement
tubes for your amplifier.
Preamp tubes aren’t worked as hard as power tubes and typically last longer. When a preamp tube
wears out, the amplifier may squeal, get noisy, lose gain and sensitivity, or just quit working. A service
center can determine which tube(s) may need replacing.
To get to the power tubes in the V-4B, the rear screen must be removed and the tube retainer(s) must be
moved out of the way. Qualified service persons may follow these steps to change the tubes:
 •Turntheampoff,unplugitandletitcoolforatleast5minutes.   
 •Removethescrewswhichholdtheperforatedmetalscreentotherearofthecabinet. 
 •Settheperforatedmetalscreenaside.      
 •Spreadthetuberetainerwingsapart,graspthetubeatitstopandgentlyworkitoutofits
socket by rocking it slightly back and forth as you lift up on it.
 •Wheninsertingnewoutputtubes,alignthetabinthetube’splasticbasewiththeslotinthe
socket and press the tube gently but firmly into place by pushing down on its top.
 •Replacetheperforatedmetalscreenandscrews.    
 •Poweruptheamplifierandletitsitforatleast20minutes.
 •Anauthorizedservicecentercanbiastheamp.