Amp has no sound when switch channels of different wattage

[shredding]

So I checked the speaker cable and it's ok. When I switch between channel 3(10 watt) to channel 2 (90watt ) all of a sudden my amp has no sound on all 3 channels. The only fix is to unplug the speaker cable and plug it back in, then it has sound again. This happened 3 times. I tried different jacks for the speaker cable on the back of the amp.... Is there something wrong with the output transformer or the power tubes ?

 

[bandit2013]

How old is your Rectifier tube? I had a similar issue as you described but was going from a 90W (CH3) to 45W CH1. Lights on the amp and all functions appeared to be working but no sound. Turned off the amp and back on, amp appeared dead. Channels would switch, lights were working but no sound. Issue was caused by a momentary short on the rectifier tube. The fuse was still good but the glass was hazed over. Replaced the Rectifier tube with a new one I had on hand and all was good. Also note: the amp failed to operate even with all channels set to 90W and diodes selected for each channel. If there is a fault in the Rectifier tube (always active and parallels the silicon diodes) it will pull the high voltage power supply down with it but there may still be sufficient voltage on the other circuits such as the heaters and control features (they are not powered by the same transformer windings as the main high voltage section of the amp). The amp did work with the rectifier tube removed with all channels set to 90W mode, do not attempt in 10W or 45W ! My thoughts are suspect of Rectifier tube.

Another thought, if you are using the FX loop set to active, did the mute light come on? I doubt this may be the issue unless there is a circuit issue with the footswitch or 8pin din cable. (Yes, this is a weak excuse for not knowing the actual cause of your issue. I would suspect the Rectifier tube to be the culprit.)