I have not touch power amp project for long time since I put my interest to R2R, a problem SA-12 come to me with distortion in one channel after a hour to play, SA-12 's design is tube in gain stage FET for output, problem is come from FET but the owner want to change to a all tubes amp and ask me to do with some parts in his hand ( pair JAN 805 transmitting tube pair WE437A pair Tangle output transformer X2.7S ). the original gain stage with too much gain (6DJ8 in two stage) so I have to take off the amp's broad only keep the case and re use the power supply for the WE437A with inter stage transformer of gain stage and put into the SE-12's case, and the output section is two mono blocks connect by cable to SE-12's case, this design can shorter the speaker cable or can put the mono block as close as possible to the speaker connect with short wire too. output power (45W) is less than the original (80W) but it can drive any speaker with feeling of powerful, the cost of this modification is not cheap, 805's power supply is 800 v and 100 ma and connection cable with silver wire etc. total parts cost will over $ 5K but the sound quality is another level
tony ma
tony ma