vibroverbus
06-15-2009, 12:32 PM
Thanks to the folks who gave me tips and suggestions on this amp - it finished up almost perfectly. Ended up being somewhat of a Tweed Princeton circuit, except more power with 6L6 instead of 6V6, and I tried the 'Moonlight' tone knob circuit (not perfect, perhaps a future re-do in the works there).
This thing has great tweedish bluesy feel, specifically it works best with the volume at 75-100% and then controlling playing volume / crunch with the guitar pot. Has some potential to get better with minor adjustments but it was built as a gift so the recipient can live with it for a while and maybe next year I can get it back to do some further tweaks. The cabinet (cost-effectively sourced from Lopoline) contains a Celestion G12C - not a perfect match perhaps but it was on-hand and perfectly workable. I'd prefer a low-wattage vintage Jensen type and was going to taste-test a few different things in there but didn't have the time.
Few interesting things - the OEM pre-amp tube in this was a metal envelope 6SC7 which oddly didn't work in the circuit. After some head-scratching i found that the first half was working great but the grid of the 2nd triode was sitting at something like -17VDC. A NOS 6SC7-GT worked perfectly when dropped in. My only guess would be that somehow some weird internal short connected one grid to the filaments which float at something like -20. Either that or the 6SC7 datasheets are flawed about internal connection/configuration... The metal tube had been working fine before, but I haven't flipped it on the tube tester to follow up yet. Also could have pulled the heater ground reference and see what happened but dint have time to fuss around for optional learning fun...
This time the after pics first, then the before...
http://www.j2c3.com/misc/FinishedOutside1%20(Medium).JPG
http://www.j2c3.com/misc/FinishedOutside2%20(Medium).JPG
http://www.j2c3.com/misc/FinishedOutside3%20(Medium).JPG
http://www.j2c3.com/misc/FinishedOutside4%20(Medium).JPG
Here's the before...
http://www.j2c3.com/misc/Hifi/IMG_0351%20(Small).jpg
This thing has great tweedish bluesy feel, specifically it works best with the volume at 75-100% and then controlling playing volume / crunch with the guitar pot. Has some potential to get better with minor adjustments but it was built as a gift so the recipient can live with it for a while and maybe next year I can get it back to do some further tweaks. The cabinet (cost-effectively sourced from Lopoline) contains a Celestion G12C - not a perfect match perhaps but it was on-hand and perfectly workable. I'd prefer a low-wattage vintage Jensen type and was going to taste-test a few different things in there but didn't have the time.
Few interesting things - the OEM pre-amp tube in this was a metal envelope 6SC7 which oddly didn't work in the circuit. After some head-scratching i found that the first half was working great but the grid of the 2nd triode was sitting at something like -17VDC. A NOS 6SC7-GT worked perfectly when dropped in. My only guess would be that somehow some weird internal short connected one grid to the filaments which float at something like -20. Either that or the 6SC7 datasheets are flawed about internal connection/configuration... The metal tube had been working fine before, but I haven't flipped it on the tube tester to follow up yet. Also could have pulled the heater ground reference and see what happened but dint have time to fuss around for optional learning fun...
This time the after pics first, then the before...
http://www.j2c3.com/misc/FinishedOutside1%20(Medium).JPG
http://www.j2c3.com/misc/FinishedOutside2%20(Medium).JPG
http://www.j2c3.com/misc/FinishedOutside3%20(Medium).JPG
http://www.j2c3.com/misc/FinishedOutside4%20(Medium).JPG
Here's the before...
http://www.j2c3.com/misc/Hifi/IMG_0351%20(Small).jpg