Bugera 1960 Bad Distortion

[JustMike]

 I took a chance and plopped down  a hundred bucks on this amp. It had very low output, but it worked. It's a Behringer clone of a 100w 4 input Marshall. I opened it up and saw a broken Molex type connector and a broken 22k resistor. I fixed both and touched up a lot of the solder connections on the back of the PC board. We've heard all the horror stories about Behringer and Bugera amps, but the PC boards and interconnects don't look any worse than those in the Asian built Marshalls I've seen. The thing that is real crap is the chassis. It's very thin steel and flexes under it's own weight when it's out of the head shell. Also, the bias adjust is strange. It has a very accessible knob on top of the chassis and a RCA jack. Their instructions say set the meter to 100VDC scale and adjust for 38.7v to 44.7v depending on the Bugera tube rating...
The tubes that it came with were redplating so I replaced them with a single pair of el34's I had, set the amp on 4 ohms and plugged it into an 8 ohm cabinet. It is LOUD and CLEAN except there is bad distortion when I play hard,almost like a crackling. Happens on high notes as well as low notes. I'm guessing this is the 4 100u Filter caps?