Sample page from Rivera R100
Contents
1. Preamp tube first aid If you hear ringing a feedback like high pitched sound in your amp it s probably coming from a preamp tube H ere a procedure to find which tube is giving you trouble With nothing plugged into either the High Gain or Low Gain inputs and the M aster controls turned down to 5 or below turn the amp on Turn up the Volume on Channel 1 and Channel 2 as well as the Reverb knob Now use the tip of a pencil to gently tap the end of each of the small tubes V1 through V5 and listen for sustained ringing Turn up the Volume and M aster knobs and keep tapping until you find the tube that rings or squeals Turn off the amp and allow the tubes to cool Now pull out the trouble some tube and replace it with one of the same value that is if you re pulling out a 12AX7 replace it with a12AX7 Testing a preamp tube Tap gen tly and listen for ringing M ake sure that the tube is oriented correctly when pulling it out or putting it back in If you look at the end of the tube and the socket you ll notice that the nine pins are arranged in an incomplete circle Always make sure the pins are aligned correctly N ever force a tube into its socket AN Remember to put the sleeve back on after you check or replace a tube Power amp tube first aid Like preamp tubes power amp tubes can go bad or wear out Your H undred Duo Twelve has four power amp tubes and if one goes bad they should all be replaced T his2. assures optimum output and tone If a power tube shorts out the HT Fuse will be blown Remove power from the amp and replace the fuse before doing the following Grip the tube firmly and then wiggle it out of its socket 1 Remove the power tubes Renember the way the eight pins are arranged and note that the center hole on the socket has a keyway that matches the center post on the tube 2 Replace one tube Turn the amp on If the fuse blows or the tube glows cherry red indicating an internal short you ve found the bad tube Turn off the amp immediately If the fuse doesn t blow replace another tube and turn the amp on again Repeat this procedure until you ve determined which tube is bad 3 When the tubes have cooled remove them Replace all four tubes D ont throw away the good tubes from the old set though save them as spares
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