Same type monitors, different resistors

[7rst1]

I am the biggest noob when it comes to this stuff. Please ask if I left out crucial info.

 

I own two Empire M-20MK II tube speakers. One of the monitors recently squealed because of a bad tube, so I cross-tested, and it checked out. I bought a new tube of the exact same type and put it in. They worked great, until yesterday.

 

The left monitor's audio with the new tube started fading out and in. I also noticed that the new tube pulsated with the music. The new tube is also much less bright than the same type of tube in my other monitor. I started cross-testing the new tube with the other speaker, and it started making that hideous squealing noise. I couldn't understand how the tube would work halfway on the left monitor and not at all on the right one, so I figured there must have been something different with these monitors on the inside. I opened them up, and now I have the two pictures attached. There seem to be different resistors in them. Is this what is causing the issue?

 

So in conclusion;

The left monitor takes both tubes just fine. I think both tubes glow less in the left monitor. Both tubes start fading in and out after a while. Sometimes I have to power off and power on the monitor in order for the audio to come back and the tube to glow.

The right monitor works with the old tube and start squealing with the new one. I think both tubes glow brighter in the right monitor.

The two other tubes on each of the monitors presumably works fine and glows identically.

 

The tubes in question are of type 6F2 and are attached below. The new one is to the right. They look identical inside. And outside

 

See the letter in the bottom left corner of the pictures:

V = Left

H = Right