I don't know the amp you're working on, but based on general principals:
The 1 Ohm resistor connects the tube Cathode to ground, giving a 1 Volt/Amp voltage drop across it. This makes for convenient reading of the Cathode current. It also means that if it got fried, there must have been a huge amount of Cathode current flowing through.
So I suspect at least 2 problems:
- the bias circuit has a fault that causes it to deliver the wrong voltage to the grid.
- the associated tube may be shorted, or damaged by passing too much current.
Pull the tubes, and measure the voltages on the Plate, Cathode, and Control Grid.
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