Voltmeter Reading - Bias Test

I decided to check the bias on my Mesa Bass 400 since I recently switched 6L6 tubes out for KT-88's and have run into some problems with a tube overheating. However, I am not too knowledgeable on this stuff and maybe you guys can assist.

The bias tester instructions said to set the voltmeter between 300-600 DC Volts. I set my meter (and old school non-digital one) to 500, which was the closest choice.

Tested the bias using the bias tester (after warming up the tubes on standby for a few minutes, then switching to power), recorded reading.

My trouble is, I am not sure which set of numbers to read on the voltmeter. The range for the DC volts are from 0-50 and from 0-250. I am not sure how these relate to the "500" setting I have it on. On a scale of 0-250, my reading would have been about 220. Is that correct?

For the sake of experimentation, I took out two tubes and tested again. The reading came out the same, surprisingly.

 

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