Hi everyone - first time posting here.
I am new to selecting power tubes, and would like to hear your thoughts on the measurements I'm getting on a new pair of Mesa tubes.
I recently bought a new duet of Mesa EL34's (STR447, Gray) to replace the old ones on my Marshall 50W plexi amp. I stuck with Mesa because I like how they sound on this amp. I also trusted their "computerized matching" process.
Problem: After biasing my amp, I get significantly disparate plate currents from this new pair: 31 vs. 38 mA. The corresponding power consumptions are 58% vs. 70% of 25W (plate at 467V). That's 18% difference between the tubes.
Question: Is this typical for Mesa's matching duets, or was I just unlucky and got a bad pair? Can I expect better if I return these and buy another pair? This is my first time purchasing power tubes so I don't know what's normal.
Thanks!
Details: The plate voltages on the tubes measured at pin#3 were both 467 Volts. Idle grid voltages were both -45.5 V. The screen resistors on my amp are 977 and 987 Ohms (within 1%). I cleaned the sockets and to rule out the possibility of contact oxidation I swapped the tubes, and the measurements also moved over exactly. Screen currents were measured as 5 vs 4 mA, which do not explain the disparity. Plate currents are measured via voltage drop across OT center tap and plates. Winding resistances are 41.7 vs 42 Ohms (<1%).
I am new to selecting power tubes, and would like to hear your thoughts on the measurements I'm getting on a new pair of Mesa tubes.
I recently bought a new duet of Mesa EL34's (STR447, Gray) to replace the old ones on my Marshall 50W plexi amp. I stuck with Mesa because I like how they sound on this amp. I also trusted their "computerized matching" process.
Problem: After biasing my amp, I get significantly disparate plate currents from this new pair: 31 vs. 38 mA. The corresponding power consumptions are 58% vs. 70% of 25W (plate at 467V). That's 18% difference between the tubes.
Question: Is this typical for Mesa's matching duets, or was I just unlucky and got a bad pair? Can I expect better if I return these and buy another pair? This is my first time purchasing power tubes so I don't know what's normal.
Thanks!
Details: The plate voltages on the tubes measured at pin#3 were both 467 Volts. Idle grid voltages were both -45.5 V. The screen resistors on my amp are 977 and 987 Ohms (within 1%). I cleaned the sockets and to rule out the possibility of contact oxidation I swapped the tubes, and the measurements also moved over exactly. Screen currents were measured as 5 vs 4 mA, which do not explain the disparity. Plate currents are measured via voltage drop across OT center tap and plates. Winding resistances are 41.7 vs 42 Ohms (<1%).
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