Hi all, I’m new to the forum. Please excuse my ignorance if this has been covered before. I have a number of questions about what the Mark I reissue expects to see in terms of output impedance when run under tweed or normal and 100 or 60 watt mode. I recently found out from talking with Mesa that plugging in a 4ohm 2x12 cab and the 8ohm internal speaker into their respective 4ohm and 8ohm jacks in the back of the amp is actually a BAD configuration. Apparently the amp handles these two loads in parallel and it is essentially seeing a 2.6 Ohm load which is a mismatch in the low (bad) direction. To make matters more complicated, I’ve been running 6L6s in tweed mode and at 60 watts, which I gather from the user manual changes and increases the effective impedance the amp expects to see. Unfortunately the manual doesn’t specify how this changes when running 6L6s, but I assume it’s happening because it does talk about this very problem when running 6V6s. The manual says: “For a proper impedance match when using 6V6 power tubes, the internal 8Ohm combo speaker should be connected to the 4 OHM SPEAKER JACK or used with a 16 Ohm speaker cabinet on the 8 OHM SPEAKER JACK. With the 60 / 100 switch in the 60 watt position, the 8 OHM SPEAKER JACK becomes a 32 Ohm jack and the 4 Ohm jack becomes a 16 Ohm jack.†So if the same kind of doubling or quadrupling of impedance is happening when I run the 6L6s in tweed/60watt mode then I might have been doing some real damage running that speaker combination at effectively a 2.6ohm load.
What would be really helpful would be to see a matrix/chart of what the effective ohm-rating for each of those speaker jacks at the back of the amp becomes when run with 6L6s vs 6v6s, tweed vs. normal, and 60 vs. 100watts. Does anyone know if such a thing exists?
The manual also shows various safe speaker mismatches and shows a “series/parallel†box. This seems like exactly what I need in order to run my 4ohm 2x12 and 8ohm 1x12 speakers out of the same amp. But I haven’t been able to find such a thing anywhere. Any suggestions?
What would be really helpful would be to see a matrix/chart of what the effective ohm-rating for each of those speaker jacks at the back of the amp becomes when run with 6L6s vs 6v6s, tweed vs. normal, and 60 vs. 100watts. Does anyone know if such a thing exists?
The manual also shows various safe speaker mismatches and shows a “series/parallel†box. This seems like exactly what I need in order to run my 4ohm 2x12 and 8ohm 1x12 speakers out of the same amp. But I haven’t been able to find such a thing anywhere. Any suggestions?
