Crate 33
This amplifier came in with a report of intermittent low volume after an hour or so.
Output stage is a 4 X EL84, parallel push-pull. The strange thing is with this chassis, the power supply is a switched mode module, rather than a standard mains transformer analogue arrangement. Personally, something that I dislike in an amplifier like this. Okay, it provided DC to the heater of the valves and is it cheaper than a power transformer and associated parts? In my opinion, a power transformer would be a safer bet as lots of Gigging amplifiers are quite often connected to the stage power via 30 extension leads powering everything from stage lights to beer chillers. SMPSs are not the most robust when it comes to this supply and when fail, it can be catastrophic. However… rant over.
Usual things seemed to be here, dry joints, poor contacts on valve bases, intermittent FX send and return, scratchy potentiometers. So, with all this attended to, a test for a couple of hours didn’t produce faults. However, the runs very hot given it’s all upside down with the heat from the 4 X EL84s and various 12AX7s cooking the chassis including the poor little SMPS. I always suggest fitting a fan to remove the collected heat from the enclosure. A 12V brushless fan connected to the CD 6.3V heater supply works okay, with silent operation.
