One of my Tubes on the Jolida 301A flickers

I was playing an LP today and noticed that each time a low frequency measure was being played, the sound was distorted. I played the same measure over again several times and confirmed the existence of distortion not previously heard. I watched the tubes while tracking through this measure and noticed that one of them was getting brighter. Thinking that maybe a tube is ready to go, I swapped it out for the adjacent one to determine if this is a tube issue. The same thing happened with the swapped tube. I tried another tube and again the same thing happened.
Has anyone had the same happen to their amp? Can you share what the root cause was?
Thanks in advance.
You question is not clear to me? When you change the tube does the problem move with the tube? Example V1 flickers and is distorted and you move that tube to say the V5 position. Does the problem move to the V5 position or does the V1 position still have the problem?

Which tube is it? KT88, 12at7 or 12ax7? If it is only one position that causes the problem you have a few things you can do. Make sure the pins are all bent so they make connection and the tube is seated well. If that doesn't fix it you will need a tech.

It will be a simple problem. Not much to those amps. A couple resistors or a cap. Could even be a pinched wire touching the chassis. The power supply is shared by both channels so I don't think that is your problem. Anyway good luck.
The problem persists on the same socket when I swap tubes. I am using EL34's and they all seem to be doing the same thing when moved to V5 position.

Thank you for the response. Sorry it took so long to update.
Check your bias! I bet the bias is off. What you mention about the tube flickering and distortion is what happens when you install new different final output tubes. get a digital multimeter, a small flat head insulated screwdriver and adust the bias to -.0040v per tube. From my experience if you want a little more base you can run the tubes a little cooler, like -.0035v If you run too cold you will loose the crisp midrange and highs. too low and you get the results you described, too high and your tubes will glow brightly and live a short life. You need to check your bias every 2 years and whenever you replace the final output tubes.
I'll check the bias tonight. Hopefully this will fix the issue.
Also, thanks for the information regarding a lower bias setting translates to more bass.

did a bias adjustment correct the problem ?
Thanks for the advise, the bias adjustment seemed to have corrected the issue.

Thanks again

I don't know if you tried different preamp tubes in your amp but upgrading the preamp tubes was the first thing I did. I upgraded the 12AX7A tubes to JJ ECC8003 gold
and the 12AT7 to Jan Phillips 12AT7WC.

The results are incredible! The upgraded tubes cost me $81.00
Jerrynsr, thanks for the info on the tubes. I'm currently running my source to a CJ pre-amp and I believe (need to check) that I may be bypassing the amp's preamp section. I'm wondering if I should use the tubes you recommended on the CJ unit?
Where does the CJ pre-amp connect to ?
I'm real happy with the sound I got out of the preamp tube upgrade. There is a major improvement over the stock Chinese preamp tubes. I didn't even need to burn in the preamp tubes to hear the improvement. The upgrade was definitely worth it for me.
The cj is now connected to a bryston 4b st. My system has never sounded better.
It's true what some say that a high powered byston & maggies are a match made in heaven. These speakers can produce deep and controlled bass.