deepblue Posted January 18, 2009 Share Posted January 18, 2009 I have looked on the web for info....I get alot of shop talk, so can someone sum it up for me? What to you physically have to do ie..tools, etc to bias or re-bias a guitar amplifier? Link to comment Share on other sites More sharing options...
saturn Posted January 18, 2009 Share Posted January 18, 2009 Wow, a guitar/music related topic. You caught me off guard ;) There was a good article on biasing I just read recently, I'll try to remember and find it then post it here. Link to comment Share on other sites More sharing options...
Slogold Posted January 18, 2009 Share Posted January 18, 2009 A multi meter and a screw driver. And, oh you should know which variable resistor to adjust to set your desired bias. Link to comment Share on other sites More sharing options...
AXE® Posted January 18, 2009 Share Posted January 18, 2009 First, remove the power tubes and measure the bias voltage at the grid (usually pin 5). Adjust the bias voltage to the most negative voltage (-50 is more negative than -40) then install the power tubes. The tubes are now over-biased and are running cool with lots of cross-over distortion. Now, connect the proper impedance load to the output of the amp and apply a 2000 Hz sine wave to the input. Turn the volume of the amp up to 70% output, or just prior to clipping. View the output waveform on the scope. Notice the notch indicating cross-over distortion in the signal. Adjust the bias control gradually until this notch just disappears. The amp is now properly biased. Link to comment Share on other sites More sharing options...
KSG_Standard Posted January 18, 2009 Share Posted January 18, 2009 Holy crap AXE! You get sexier every day. Some amps are easier to adjust the bias on than others though, right? On some amps you might have to replace resistors, others have an adjustment? Link to comment Share on other sites More sharing options...
Guitarooster52 Posted January 18, 2009 Share Posted January 18, 2009 First' date=' remove the power tubes and measure the bias voltage at the grid (usually pin 5). Adjust the bias voltage to the most negative voltage (-50 is more negative than -40) then install the power tubes. The tubes are now over-biased and are running cool with lots of cross-over distortion. Now, connect the proper impedance load to the output of the amp and apply a 2000 Hz sine wave to the input. Turn the volume of the amp up to 70% output, or just prior to clipping. View the output waveform on the scope. Notice the notch indicating cross-over distortion in the signal. Adjust the bias control gradually until this notch just disappears. The amp is now properly biased. [/quote'] ...so you need a multimeter, signal generator and an oscilloscope. Maybe a lesson on safely as well...so the average guy in these forums may be better off taking it in to be biased. I'm sure there's a recommended voltage level for most amps that that would provide a shortcut though???? Link to comment Share on other sites More sharing options...
KSG_Standard Posted January 18, 2009 Share Posted January 18, 2009 Plus be careful what you touch, electricity can hurt. Link to comment Share on other sites More sharing options...
saturn Posted January 18, 2009 Share Posted January 18, 2009 This is pretty good IMO. It even has video links. Even though, I don't know if I trust me enough to try this myself. http://www.eurotubes.com/euro-video.htm Link to comment Share on other sites More sharing options...
AXE® Posted January 18, 2009 Share Posted January 18, 2009 My guy uses these... http://biasking.com/ Link to comment Share on other sites More sharing options...
urbs Posted January 18, 2009 Share Posted January 18, 2009 Try the guitar tricks website , I rebias my amps myself . It's not that difficult to do but remember that it can be a shocking experience . I think its www.guitartricks.com . You can probably find someone with your application on their forums . Link to comment Share on other sites More sharing options...
surfpup Posted January 18, 2009 Share Posted January 18, 2009 I bought a bias probe from Eurotubes (the previously posted video link). Plugged my multi-meter into it and 5 minutes later my Deluxe Reverb was perfectly biased. Good thing too - the tech who worked on it for me last had it set very cool (17mA). Once I got it back up to 28mA it warmed up considerably. The instructions on the Eurotube site are great and easy to follow. Link to comment Share on other sites More sharing options...
Californiaman Posted January 18, 2009 Share Posted January 18, 2009 Now this was a useful post. Good job Axe. Link to comment Share on other sites More sharing options...
deepblue Posted January 18, 2009 Author Share Posted January 18, 2009 As always gentleman...great advice. Thank you all. Link to comment Share on other sites More sharing options...
Murph Posted January 18, 2009 Share Posted January 18, 2009 My Mesa is fixed. I change the tubes every 5/6 years and................. BOOGIE......... Murph. Link to comment Share on other sites More sharing options...
Slogold Posted January 18, 2009 Share Posted January 18, 2009 My Mesa is fixed. I change the tubes every 5/6 years and................. BOOGIE......... Murph. My BOOGIE Tubes are still the original since 1997 and still rockin. Link to comment Share on other sites More sharing options...
Dynadude Posted January 18, 2009 Share Posted January 18, 2009 Lots of older Fender amps have a "Hum Balance" adjustment on the back. You don't even have to pull a tube, just insert a flat blade screw driver and turn the adjuster either direction to balance the input/output. When it's at the quietest setting, you're done. Link to comment Share on other sites More sharing options...
MReynolds Posted January 18, 2009 Share Posted January 18, 2009 My Mesa is fixed. I change the tubes every 5/6 years and................. BOOGIE......... Murph. Yep. Buy a Mesa...no bias adjust necessary. Link to comment Share on other sites More sharing options...
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