tube amps ground loops
Hi Bob/Frank
I haven't got the chance to test the different sound modifications yet. I tested the amp yesterday on the big 4x12" cabinets and it realy sounds awesome. But it's getting way too hot. After 1 hour the amp was loosing it's power because of thermal stress, I think. The amp was standing upside down so the heat from the output tubes was going directly towards the chassis, I could not hold my hands at the rear side of the chassis!
This limited the test, but I will install some fans cooling directly at the power tubes.
I compared the noise level with a carvin legacy and the marsahll stack and in comparison the amp is very quiet so I am fully satisfied with the result!
I've desoldered the J175 (2n5460) and measured 450kohm across the 475k grid res at V2a, so installed a 22kohm res in series. This cured the clipping at V2a for channel 1. However, the basicaly don't have any headroom at all! If I turn the master 0.5 - 1.5 out of 10 (at any channel) the amp is LOUD. The marshall amp will have to be at 6 - 7 out of 10 to get that loud. As I wrote, I've desoldered the J175 (2n5460) at V2a grids which function might have something to do with this issue.
So guess I still have some issues to solve..any suggestion are welcome
Bob, As Frank wrote the amp is very very flexible (notice for example the switchable power supply. besides the rectifier selcetion it also had the Spongy/Bold switch at the primary which as I understand will give the amp more or less voltage/gain!)
what changes would you make to the schematic?
Added after 10 minutes:
One little thing! We are recording some new songs right now and offcourse we recorded the amp. This was how we noticed the power drop since the record in level bacame lower. However, my friend deleted (unfortunately) the recordings and we had to switch to the marshall stack. This was here the fun thing took part! We all realy noticed how different the two amps sounds and we decided to put the recordings on hold untill my new build is finished
Offcourse this don't mean that the marshall is bad sounding, it's just an expression of that we're all damn tired of the marshall sound!
Thomas