I have KT66's in my JTM45 and I like them. They do seem a tad mushy but I attribute that to the plate voltage on my build (about 400V). I have another amp that uses 6L6's and it seems to be more punchy with more clean headroom than my Kt66's, but the plate voltage on that amp is over 450V. I have both amps biased about the same, around 42mV. I've tried higher bias adjustments and the amp with the 6L6's seems to respond better than my lower voltage Kt66 amp. Raising the bias on it doesn't seem to do much, but my 6L6 amp really gets punchy with hotter settings. The clean headroom still seems to be there even with a little hotter bias setting. The kt66 amp doesn't seem to change that much with bias adjustments, but I suppose it would show itself at higher volume levels though. I don't know... I guess the lower plate voltage is needed and does sound real good, but I can feel it when I play, but I only guess that is because of my other amp has over 450 volt plates. That voltage does make a difference I guess. But all in all my JTM45 build is my favorite amp I've ever owned.
By what i've read about iron the Mercury Magnet iron gives more clean headroom than the Metroamp iron I used in my 45 build. And I think there is a difference in iron for Kt66/6L6/5881 tubes and El34 tube amps. The latter I believe you use 50watt plexi trannies. I don't remember..... They'll work with the other tranny but I think I remember reading why it's better to change them to the 50 watt plexi type instead. Again, my mind fails to recall the exact reasons why.
All this info is pretty easy to find on the metroamp forum. I've read it all there before but its been awhile ago.
Very nice. Thanks MBD115. I suppose my only remaining question is regarding the plate voltages for the JTM-45. I see that one can purchase lower voltage PTs (300-0-300 vs.. 350-0-350) which end up dropping about 100v overall once you get to the power tube plates, and I'm wondering what the consensus is regarding "ideal" plate voltages for a JTm-45.
I personally find that, all things being equal (which they rarely are), I find I prefer lower voltages in a given amp, as I'm not a fan of the tight/clean high-headroom thing, but rather the textured/squishy/vibey/dirtyclean low headroom thing. Any recommendations?
Thats what I was trying to say my around 400 volt plates feels like
Best of luck dehughes.
Very nice. Thanks. That sounds perfect.
I know it is a subjective question to ask, but would you say that having lower B+ voltages is a detriment to the JTM-45 platform? I ask because with some amps I find that higher (r.e., stock) B+ voltages really do the platform justice, yet with others, lowering the B+ gets it feeling nice and vibey...
dehughes wrote:I know it is a subjective question to ask, but would you say that having lower B+ voltages is a detriment to the JTM-45 platform? I ask because with some amps I find that higher (r.e., stock) B+ voltages really do the platform justice, yet with others, lowering the B+ gets it feeling nice and vibey...
I would haft to say "yes", but I will also say I'm probably wrong. I read where some have raised the voltage to over 450v and report they like it better. That clip someone linked us to on your page #1 was a delight to listen to and I'd say that was some below 400v plates.
If I were building this amp all over again I would again opt for the lower plate voltage. One reason would be when one starts digging-in with a little lower plate voltage I think it can be felt as well as heard. (that probably sounds stupid)
