Jolida Tube amp lost output one channel

So I seem to have lost output on the left channel of my Jolida 102B amp. Is it safe to assume it's the tubes and I should just replace them? All of them? I just picked this up a couple weeks ago so would hate to throw money at a lemon. I did have the speakers hooked up ass backwards, meaning they are 4-8ohm speakers and I unwittingly had one on 4 and one on 8 so maybe I damaged something more than the tubes? But, it has been working fine until I powered it up today and after the lack of sound I noted the mis wiring (it's only been that way about a week as I was trying out different speakers). Yeah, I've got a ways to go, please help?
Most of the time replacing bad tubes will solve problem but to play it safe, ID the bad tube even without swapping them from channel to channel connected to dummy load 10Ohm/10...50W resistor since the bad one will either glow with crazy colors or would not glow at all. A dummy load resistor (you can purchase at partsExpress) may save your speakers if anything goes wrong(such as anode voltage applied to terminals and fuse didn't blow on time). If you can't ID the tubes, swap them between channels one by one and test sound. I have always handy single cheap speaker driver that you can purchase in WalMart car audio section the cheapest specked to 8 Ohms.
Your miswireing might cause tube go bad in most of cases when the tube is already going bad or you rocked your music to high with misconnected channel.
Swap the tubes from one channel to the next. If the problem follows the tubes, you have your culprit. If not, it's not the tubes...

Thanks, both pre amp tubes tested bad today. Replaced with some old stock Telefunkens and good to go (probably should have gone with something a little less than Telefunken but....)

what was weird about swapping the two 12AT7's that tested bad is one channel would work just fine and one dead, when I'd swap they'd both play sound just one was much quieter. Thinking I need to get the rest of my tubes checked.