Hi Kats. Very cool! That is a funny coincidence. Your build really is very close to what I am thinking about doing! Also, when I built my 50 watter, also about a decade ago, I had a hard time deciding whether to build it or a JTM 45. I would love to have a JTM 45 or 50 as well... I love the singing, vocal quality to the midrange that they have and the bit of chime in the high end, not to mention the amazing sag in the attack.kats wrote: ↑Tue May 21, 2019 1:16 amHi DanHalen!
Co-incidentally, I'm in the middle of a similar build that I put on hold almost a decade . Nothing much to offer other than friendly chit chat Late '67 build, Marstran xformers (1202-132/ 1203-80). 3H choke
I'm starting out filtering 100/100 mains, 32/32 screens, 32 PI, and 32+32 preamp. Shared cathode, single rectifier, 470k mix resistors, 27k on 16ohm NFB. Modern CF resistors except the long ones are CC, mustard signal caps. The only thing I'm humming and hawing about is the 2@ 1k5 or 4@ 5.6k grid stoppers (stupid, I know...) and I'm gonna start out by using the two voltage droppers (8.2k + 10K). I decided to use modern el34's, let's see how long I can control myself . My last build was 10 years ago (JTM45) which I just love, but I've always been drawn to 100 watt amps so I went this route. I use an attenuator.
Oh yeah, I put a pull/push knob o the bright channel with a 5000pf cap.
The only thing is the xformer wait times are quite long - at least 5 weeks.
Also just for conversation: my 50 watter was my first amp build, so I probably won't be posting any gut shots! It sounds great though. It is a basically stock 1986 specs, Metroamp kit with George's transformers. No bright cap, nfb 27k on the speaker jack. I thought I preferred it through 8ohms (slightly lower nfb), but lately I have actually been preferring the slightly higher feedback at 16ohms. Then again, a lot of that tonal bliss has to do with the amazing sounding 4x12 cabinet that I recently got... I tried so many variations with the amp, lead spec, bass spec, various halfway combinations, every different bright cap, cathode bypass caps etc. In the end I settled on bass spec and the only 'mod' it has is lower than stock filtering on the PI and Screens (I swapped out the 50/50 can for a 32/32 can). I have it on the bench now to fix a worn input jack (it has had a lot of use!). I think I might mess around with the lowering the mains filtering, just for the heck of it. It does sound great as is though. I am fortunate to have a recording/rehearsal space where volume is not an issue. I generally do not play it with an attenuator there. It has been a while since I have gigged with this amp, but when I did I always brought an attenuator but did not always use it. Depended on the venue of course and I was not running the thing on 10 either... Oh and at the time I was using a 4x12 with Celestion heritage 20w speakers, which would knock off a bit of volume (I'm digging G12h speakers more these days). I used to always say that I would post a clip of it and I am not sure if I ever did! I should really do that just for kicks.
Your amp build is exciting. You should post a clip when it is done! Over the last weekend, I was thinking maybe I would veer more towards 10000 series with my build. Funny how we agonize over the little details and drive ourselves crazy. For you it's the grid stoppers, for me it is the dual vs single rectifier. I guess maybe we enjoy fussing over that stuff, who knows. In the end, either way would probably work out fine (speaking for both of our situations there...).