dying amp

[trinic]

Can amyone help me on my amp, I'm new to this but trying to learn, I have an acustic G100t amp and I can't read low voltage on it coming out of the tranny, I can read high voltage, and the neg voltage if is ok and plate voltage is 430 and it was at 490, then it went down to 460 and now it is at 430, the amp plays good for bout an hour then it dies.

[tubeswell]

change the tubes and report back