Peavey 5150 no bias on one valve.

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So I did the bias mod on my 5150, plugged in my bias probes and then my new tubes. One of the inner tubes does not have any bias voltage. I checked the tube and the probe and they are both good. Could this be a screen grid? Where are the screen grids located? thanks

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Nevermind... I'm stupid. It was a screen grid. Now somebody help me get my Splawn sounding good!