Help: Tube Amps Pops Speaker Cone

I'd send those babies back for a check up.

Actually, this didn´t work for long. The sputtering is back, sporadically. The distributor has told me that it will not damage my speakers and that I can use the amp as it is. But I now need to turn the amp on, wait for a hum, turn the amp off, and then turn it back on, before it functions.

I think I solved the popping problem inadvertently without changing a capacitor. I simply took out the VV52B output tube and firmly reinserted it. Popping was gone upon next start-up. What is this a sign of? A defect with the tube contacts? I think another audiogon member said that he fixed a sputtering problem on a Jadis push-pull amp by pushing down on the output tube while it was in operation. Why does this work?

Thanks Liguy. Looks like I have to ship this amp back to the workshop. The popping problem is in only one of the monoblocks. The humming problem is in both. Also, I forgot to mention: there is a buzzing coming from the transformers of both that cannot be eliminated with line filters or better AC cables or cheater plugs or ground switching (I did not go into the chassis to see if the screws are loose). And, finally, a little detail, these particular amps had to be precisely adjusted by a technician to my house voltage (because it was a little lower than standard) before I could use them. This adjustment was necessary because the heating of the tubes and their grid voltage is unregulated. Is there a SET web site or SET FAQ somewhere that deals with malfunctions?

Without seeing a schematic of your amp all I can do is venture a guess. Some SET amps have outputs that are capacitively coupled to your speaker. The capacitor is there to keep DC of of your speakers. It could be that this capacitor is breaking down. If you are witnessing this in both channels the problem is probably a bad or breaking down power supply filter capacitor. This problem is consistant with the Hum you are hearing also. In either case you are risking damage to your speakers and or amp by using it in this condition. The repair is pretty straight forward but I recommend a pro doing the job if you do not feel comfortable as a faulty repair can do much more damage than you care to deal with. Best of luck and I hope you enjoy your amp for many years to come after it's repair.