Lower power on left channel

I’d work back from the speakers. Swap the speaker cables at the back of the amp. If the trouble follows the swap, you’ve ruled out your speakers. Swap the cables back.

Next swap the cables from the preamp. If the trouble moves, it’s the preamp or source. Swap the cables back.

Swap the cables from your source. (CD, DAC, etc). If the trouble moves, it’s your source. If it doesn’t, you’ve ruled out everything else and it’s your amp. Swap the cables back.

Now you can start swapping tubes around with some confidence to help pinpoint things. If tube swapping doesn’t make any difference then you have another issue with your amp and unless you’re well versed, you might need to seek professional assistance.

Almost my entire career was in IT, both hardware and software. The trick to this kind of troubleshooting is no trick at all. It’s being methodical and thinking the problem through. Best of luck!

Happy listening.

Hi Guy's

I have not checked the red light (bad tube indicator) I did not notice that any of them where on when leaning over the amp checking the heat of the tubes before turning the amp off, I will have to power the amp and check at the same time as changing the speaker cables over. Source wise, I have  tried change the input on the pre amp from Dac to phono pre amp, that did not make any difference.    

Addendum to my previous response-I have a non contact infrared laser pistol grip thermometer that has many uses.  Just added checking Amp tube temps to it's portfolio.  Got it at HF (20:1 ratio for less than $40 with coupon) originally to check header pipe temps on engines..  Very accurate on tubes also.

@bigred71 

 before you swap the wires, swap the tubes. Wires rarely go bad, but tubes often do.

All the best.

,