WOW! I had a matched pair of GT E34L stashed away I robbed from my 6505+ and decided to give them a try in the Origin. I know the Origin is cathode biased so I am hoping these are ok in the Origin because they "ROCK!". Literally hesitated to even bother because my OCD tells me that traditional Marshall is and should EL34. I am not knowledgeable about the E34L other than seeing them used in some American style amplifiers, so again my OCD was telling me this is gonna take away the "authenticity" but boy was I wrong. This Origin20 screams and reminded me instantly of a hot JMP 1959 I played years ago. There was definitely an increase in powertube distortion, Marshall crunch, karange and sizzle galore, what was a fantastic amplifier to begin with was perfected to my taste with the E34Ls. The bass was full but noticblely tighter and the mids a little more pronounced but all sounding distinctly Marshall. Anyways I hope someone can chime in and confirm the E34Ls will be OK with the cathode bias because man I hate to have to remove them. Simple way to describe it in my opinion, it made it sound more Marshally. If these are safe for prolonged use in the Origin I highly recommend giving them a try, especially someone looking for a little more gain and distortion out of the Origin.