Members bmast160 Posted April 17, 2008 Members Share Posted April 17, 2008 changed the stock EL84's to JJ EL84's...does this amp need to be biased...and/or can it be? Link to comment Share on other sites More sharing options...
Members bmast160 Posted April 17, 2008 Author Members Share Posted April 17, 2008 ... Link to comment Share on other sites More sharing options...
Members gt5litre Posted April 17, 2008 Members Share Posted April 17, 2008 The amp uses a self bias circuit (bias is accomplished by a cathode resistor) so you need a matched pair of tubes. Link to comment Share on other sites More sharing options...
Members meringue Posted April 18, 2008 Members Share Posted April 18, 2008 no biasing is needed as it is cathode biased. plug any matched QUAD of el84's you like and play!! Link to comment Share on other sites More sharing options...
Members bmast160 Posted April 18, 2008 Author Members Share Posted April 18, 2008 and the same goes for a vox ac30cc2 right? cathode bias so doesnt need biasing after switching power tubes? Link to comment Share on other sites More sharing options...
Members bmast160 Posted April 18, 2008 Author Members Share Posted April 18, 2008 ... Link to comment Share on other sites More sharing options...
Members Weathered Posted April 18, 2008 Members Share Posted April 18, 2008 and the same goes for a vox ac30cc2 right? cathode bias so doesnt need biasing after switching power tubes? Correct. You can actually switch the cathode resistor from 50 ohms to 82 ohms, which runs the tubes a little cooler. That's the "bias" switch on the back. Link to comment Share on other sites More sharing options...
Members bmast160 Posted April 18, 2008 Author Members Share Posted April 18, 2008 Correct. You can actually switch the cathode resistor from 50 ohms to 82 ohms, which runs the tubes a little cooler. That's the "bias" switch on the back. well thats easy enough...should the bias switch be on any particular setting for certain brands of EL84s as opposed to others...i usually just leave the back switches on "hot" and "modern" to get the amp closer to running class a Link to comment Share on other sites More sharing options...
Members Weathered Posted April 18, 2008 Members Share Posted April 18, 2008 well thats easy enough...should the bias switch be on any particular setting for certain brands of EL84s as opposed to others...i usually just leave the back switches on "hot" and "modern" to get the amp closer to running class a It's totally about taste. The AC30 isn't really Class A in any iteration. The modern setting just changes the power supply filtering from 22 uf to 44 uf, which changes the feel of the amp. I also run mine with the switches in Hot and Modern, but I may try the lower filtering at band practice next week for giggles. Link to comment Share on other sites More sharing options...
Members lunarian1 Posted April 22, 2008 Members Share Posted April 22, 2008 "Correct. You can actually switch the cathode resistor from 50 ohms to 82 ohms, which runs the tubes a little cooler. That's the "bias" switch on the back." how would you do this ? Link to comment Share on other sites More sharing options...
Members Weathered Posted April 22, 2008 Members Share Posted April 22, 2008 On the AC30CC series, there's a bias switch on the back that changes the Rk for the power tubes. Link to comment Share on other sites More sharing options...
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