I'm having a similar issue on my DT25. I power it on and once everything is warmed up it sounds great. But then after 10 mins or so it will fade in and out. By this I mean the volume will gradually go down on its own and then come back to full strength after a few seconds. This repeats every 3-5 mins.
I replaced all the tubes with the ones recommended on this forum by psarkissian and dialed in the bias correctly. Still no resolution. My question is - is this a known issue and an easy / low cost fix? Great if you can give me some insight on this as I want to determine if the cost to fix is worth it.
