Question issue with fatman iTunes mk2

[tubebuddy]

hi
i have a fatman iTunes mk2 valve amp with fresh tubes, very quiet & sounds great but after 20-25mins, the sound degrades!!! sounded fuzzy. had to switch off but when you return a bit later & start again, its sounded good but again after some time, the harmonics just become 'fuzzy'
any idea what the issue might be??

 

[Mark.Yudkin]

Sounds like you need to get it repaired (likely defective "fresh" valve, but might be something else) [and I also guess you mean Fatman iTube MK2]. The manufacturer will be able to sort it out.