Members burton4snow Posted March 25, 2011 Members Share Posted March 25, 2011 Getting some weird cutting out at high levels. Think it might be preamp tubes. Can I just switch these out without having to biase the amp? There are 3 of them 12ax7s. Which changes your tone more on an amp the preamp or power tubes? Link to comment Share on other sites More sharing options...
Members burton4snow Posted March 25, 2011 Author Members Share Posted March 25, 2011 bump Link to comment Share on other sites More sharing options...
Members mrbrown49 Posted March 25, 2011 Members Share Posted March 25, 2011 Yes only power tubes need to be biased. IMO preamp tubes matter more in modern amps because that's where most of the grit comes from, especially with master volume amps. Link to comment Share on other sites More sharing options...
Members Wyatt Posted March 25, 2011 Members Share Posted March 25, 2011 Well, the Rebel offers a unique diagnostic option. If you use tube mix for full EL84 and then full 6V6 and the treble is still cutting out, you can eliminate the power tubes are the problem. In most preamps, V1, the tube closest to the input is the most important because it usually includes the first gain stage (12AX7's are two triode tubes in one envelope, each half gets used separately)...and since it's a linear progression through the amp, every stage amplifies the preceding stages. But apparently, that's not the case with the Rebel, on the Rebel. V2 is the first tube used, then V1 then you go to V3 (the Phase Inverter, the 12AX7 closest to the power tubes). Before replacing every 12AX7, I would take a known good 12AX7 and use it to replace each tube in each position...V2 first, then V1, then V3 and see if you can find a weak link. It may also not but a tube issue, you may be losing high end do to capacitance loss somewhere like the effects loop. If I could find a schematic, it would be easier to find potential problem spots. Link to comment Share on other sites More sharing options...
Members Funkwire Posted March 26, 2011 Members Share Posted March 26, 2011 Have you been to the Egnater forum on rig-talk.com? Bruce and Ian Egnater both frequent there and answer questions. Link to comment Share on other sites More sharing options...
Members Ian Egnater Posted March 28, 2011 Members Share Posted March 28, 2011 Have you been to the Egnater forum on rig-talk.com? Bruce and Ian Egnater both frequent there and answer questions. I frequent here too! If you're having an issue still though, feel free to shoot an e-mail to nate@egnateramps.com, and he'll be able to help you out. Link to comment Share on other sites More sharing options...
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