[Refugee]

If you do not have an isolating transformer take all the valves out and put them in a padded box.
Power the amp up and check all the AC voltages from the transformer.
If the transformer is good add a 1N4008 diode in series with a 200k 2W resistor in place of one section of the rectifier valve and leave it powered for a few hours until the voltage climbs up on the capacitors.
If they turn out to be open circuit you will get hum when you later power it up with the valves in.