sluckey wrote: ↑Fri Jan 10, 2020 1:44 am
You can put 6L6s in the amp. No changes required. But... the yellow 4Ω tap becomes 2Ω, the green 8Ω tap becomes 4Ω, and the orange 16Ω tap becomes 8Ω. Don't expect any more power.
Steve,
Is that a general thing when going from a pair of 6V6's to 6L6's? I ask because my Tweedle dee runs 6L6's now and I never thought about the OT impedance. Its been running fine by the way. Should I do as you say and run the 8 ohm speaker form the 16 ohm tap now?
Yes that's a general statement. 6L6 plate impedance is typically about 1/2 that of a 6V6. So if you have an OT that is made for 6V6s (8K to 4,8,16 in this case) you would want the OT to reflect about 4K on the primary side. You can easily do that by halving the speaker impedance on the secondary.
Also, my general understanding, please correct me if wrong, is that the tubes still do just fine about one impedance mismatch away (4 to 8 or 8 to 4 etc) and work fine, but you're not at the optimal impedance for the tube and therefore often out of the best range in the tube curve chart, ending up being less efficient, less powerful, etc. Still works, just sounds different and maybe 'ok'. I've actually played a bit once I got an impedance selector installed on an amp, trying different impedances on an 8 ohm cab, 4, 8, and 16 and could tell they all sounded different and I definitely preferred the amp at 8 ohms for the 8 ohm cabinet.
thanks Steve, i did a bit of googling and read up about it its basically the same as using the half power switch on my Dumble amps.
When Larry Carlton used my #102 rig he purposely mismatched the the speaker to get the tone/amp response he liked. Isn't the JTM45 technically using the 'wrong' OT impedance for the output tubes?
its basically the same as using the half power switch on my Dumble amps.