[Mondial]

Address the bias issue before anything else. The coupling caps certainly can wait, as the originals are the equivalent of  Sprague orange drops and are most likely fine as is.

Bias supply at -15 V is a problem as it will make the output tubes draw excessive current. The selenium rectifier is the cause and you can replace it with four silicon rectifier diodes on a terminal strip, or a packaged bridge rectifier like this:

http://www.ebay.com/itm/BR-62-Full-Wave-...xy2O1SZ~8v

In the meantime until you can replace it,  connect a 1K resistor across R126 (5.6K) to increase the bias at the output tube grids to the proper value.

You want at least -14.5 V at each of the output tube grids to protect them.