One tube pulsing in a quad

[jerryjg]

I have a amp, a Bogen amp that one tube in the quad of 4 7868's is pulsing al ot brighter than the others. Doesnt matter which tube I put in that position. Also, once it arced- hadn't been fired up in awhile.  The two front tubes make a very high pitched squealing  noise when pressed down sometimes- not all the time. Any ideas whats going on here.
I played the amp for a good long while and it does seem to run cool and no issues besides that one flare up of the tube and the bright pulsing of it. Loose tube pins?

[John]

One of the guys will probably tell you to make sure there's not a "channel" burnt between 2 of the terminals on the pot, and to make sure you don't have any bad solder joints.