#1
How do I tell if I need new tubes in my 75 Pro Reverb and yes they have been changed before but just for general maintaince .So what are the signs of them going bad? the 6L6s look to be glowing fine.
#2
If you play at lot at high volumes its a good idea to change your power tubes about once every 6 months. If you just use it for a practice amp then you should be fine changing your power tubes once a year. Pre-amp tubes can last for a long time. But I recommend changing them once a year as well. Just for good measure.