Speaker diagnostic question

OK, so I reached out to the person who rebuilt my amp. He has been very responsive in helping me try to figure this out. Anyhow, he suggested I reseat all the tubes on the circuit board and then take the end of a screwdriver to gently tap those tubes while a record was being played. After reseating the tubes, I turned it on and everything worked for about 30 seconds. When the music cut off I tried taping and was able to get the music to cut back on for a few seconds. So, it appears to be an issue with one or more of those tubes.

As I look back upon this, I realize the error in my ways. For those not familiar with the layout of the 2150 and the 532 amp, the amp is mounted along the side. The tubes, therefore stick out from the side. The plug for the speaker is located at the farthest point at the bottom. So you have to snake your arm through the wires for the changer and relay box, and across the amp to get to the plug. As careful as I was being, I'm confident that I would never have known if my arm was brushing up against the tubes. In fact, it would be extremely difficult not to lightly touch one or more of the tubes. So while I was wiggling the plug, I was likely occasionally 'tapping' one of the tubes causing the sound to come in and out and making me 100% certain it was the plug.

I'll update more once Bill gives me next steps; however, I wanted to provide an update.
Thanks
Brooks