Mesa's are generally one of two types: unadjustable fixed bias and cathode bias
The fix bias amps require that you buy tubes in the correct bias range. Because the fixed bias point isn't adjustable (no bias adjustment pot), the tubes have to be selected to work with the bias voltage preset in the amp. IME, tube suppliers like the Tube Store know which range of tubes common Mesa's require, if you tell them which specific amp you are buying tubes for.
Cathode bias is basically self biasing (no adjustment required).
I believe the Studio 22 is an EL-84 amp? That won't really help because I have two Mesa EL84 amps - one is fixed bias and one is cathode bias. If the manual doesn't specify what type of bias that amp uses, either 'The Boogie Board" or Mesa themselves can help you. Shoot Mesa an email - they are one of the best out there with customer service.
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