What should I check if I wanted to buy a used guitar amplifier? if it of valve or tube, what should I take on count?

         > Iszil

You can check the light of the tubes while working. The heat wires must have a light orange colour. If there is gleaming a blue light this indicates that the tubes are old and have to be changed. Sometimes if this happens they are broken and there is air in the tube.
The knobs dont have to scratch while turning up and down even the plug contacts while plugging the cables in and out. Mostly a contact spray helps out. Take care of rust this means that the amp stood in wet rooms.

The Amp should'nt take longer than half a minute to hear the first tone and is ready to rock. Pay attention of humming and noise when you turn the volume to the highest level without any gear plugged in. Hummning means that there are probs with the power supply. Unnormal white noise may indicate a pre state of blue gleaming in the tubes. No feedback should be heard. You should hear a healthy warm noise coming out of the speaker when you do this. Overdrive should function. So take YOUR guitar to the amp. You are the best judge for a new sound.

If you are in contact with a serious salesman he lets you take a view into the amp.
Probably you can take the amp with you at home so you have the time to check out the amp for one or two days.

Perhaps this is what you knew before on the other side GOOD LUCK

TK