As I have posted recently I just finished a couple of amps. The JTM45 1x12 has taken a bit of tweaking to get dialled in - this is actually part of amp building I really enjoy. I started out with KT66s in it but found them a little too bright, so swapped to KT77s, which sounded a lot better for what I'm used to. The amp is fairly true to the original schematic except that I have a 10µF bypass cap on the first stage instead of 220 or 330µF. Those huge caps make it waaaay too bassy. Understandable of course - it is a copy of a Bassman. I also used the later Plexi values of 500pF and 33K in the tonestack and removed the bright caps on the bright channel volume and mixers. I might put the mixer cap back on though...
I had a hunch that I may have inadvertently overbiased the KT66s originally. So I reinstalled them and biased again. This time I had to change a resistor on the bias pot as I couldn't cool it down enough otherwise. So obviously I had cocked something up the first time around. So now the amp is running a pair of JJ KT66s biased at exactly 60% and it sounds wonderful. The sound is kind of like a 6L6 without any mid-scoop and smoother highs. Originally they did sound a bit scooped, but that was because they were biased too hot. Over-biased amps do tend to sound too bright. Now it's approaching Fender tweed tones but with a tougher, punchier low end.
I was pretty pumped about this so over coffee I explained (as briefly as I could) to my wife about how important the proper biasing of power tubes is in tube amplifiers and how getting it wrong affects tone. I also explained how the KT66 sounds different from the KT77 and how Marshall copying a bass amp made for a very bassy guitar amp. She looked at me with that look that patient, understanding wives get and assured me that she will sleep more soundly tonight because of what I have just told her. I think the important take-away from all of this is that even though you think your partner may not understand the technicalities of guitar amp design and even pedal design obviously, they understand enough that your explanations can help them sleep better. Even as you explain it all.
I had a hunch that I may have inadvertently overbiased the KT66s originally. So I reinstalled them and biased again. This time I had to change a resistor on the bias pot as I couldn't cool it down enough otherwise. So obviously I had cocked something up the first time around. So now the amp is running a pair of JJ KT66s biased at exactly 60% and it sounds wonderful. The sound is kind of like a 6L6 without any mid-scoop and smoother highs. Originally they did sound a bit scooped, but that was because they were biased too hot. Over-biased amps do tend to sound too bright. Now it's approaching Fender tweed tones but with a tougher, punchier low end.
I was pretty pumped about this so over coffee I explained (as briefly as I could) to my wife about how important the proper biasing of power tubes is in tube amplifiers and how getting it wrong affects tone. I also explained how the KT66 sounds different from the KT77 and how Marshall copying a bass amp made for a very bassy guitar amp. She looked at me with that look that patient, understanding wives get and assured me that she will sleep more soundly tonight because of what I have just told her. I think the important take-away from all of this is that even though you think your partner may not understand the technicalities of guitar amp design and even pedal design obviously, they understand enough that your explanations can help them sleep better. Even as you explain it all.
That's great! I'm stealin that one.
