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5881WXT bias?

6/1/1998 5:24 PM
Dinko
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5881WXT bias?
Hello,  
I have seen your e-mail adress on Tube amps FAQ. I need  
some help with my Fender Dual Showman reverb,(100 watts,  
master volume, mid 70s).I rewired everything to blackface Twin reverb specifications:drilled holes in  
circuit board and routed wires as on AB 763 Twin, repla-  
ced filter caps, power tubes (with Sovtek 5881 WXT),all signal capacitors and resistors,pulled out the master volume, and made the adjustable bias control.This amp has a voltage selector for use in European countries (110 to 240 V wall AC).Since my amp had about 500 volts on output plates (with voltage selector set at 220 V, which is standard supply in my country), I turned the selector to 240 in order to approach the desired 460 V on the plates.Now the plates have 457 V, heaters have 6,1 VAC, and bias is from -46 to -52 VDC.I thought that now the amp will sound better but it don`t.It wont stay clean if tone controls are above 4.I tried it with different bias settings without improvement.Is it possible that 5881 WXT tubes need different bias range or are they just too "new" yet to operate properly (10 hours so far)?Is 6,1 VAC enough for filaments?  
Also, I didnt rewire ground wires from filter caps.I have read somewhere that the ground from driver tube filter cap should be near the power trans.-mine is under normal channel tone pots.  
So, if you can help me with this in any way, please do, it will be most appreciated.  
Thanks! Kindest regards.  
 
Dinko

 
Replies:
Jim S. A filament supply voltage 6.1VAC sh... -- 6/2/1998 5:23 PM