Fender Vibro Champ XD Trouble

[Spanky]

It had been sitting for about 2 months and when I went to turn it on I could hear a horrible electronic crackling noise. I looked at the back of the amp where the sound came from and I witnessed the 6V6 power tube burn up. I could smell it and upon visual inspection,looks like inside had some connections melted. I ordered a brand new 6V6 and a 12AX7. After installing the new tubes and turned on the power supply the tubes glowed and seemed to warm up as they should. No sound at idle. Turned up the volume and still nothing until you get to 9 or ten then you hear a very choppy distorted sound. I tried a new cable took the chassis out and inspected visually,no burned up components, no smell of burned parts and no loose connections. Are there any known problems I need to look at? Thanks in advance Norm