GA-90 fuse size

[malti]

I would like to know how to calculate the correct fuse value for a 1953 Gibson GA 90 amp. The schematic that I found does not depict the fuse.

[sluckey]

Set your meter to measure several amps of AC current. Connect the leads across the fuse holder. Remove any fuse. Turn the amp on and let it warm up a few minutes. Note the meter reading. Now double that reading and use the closest available slo-blo fuse.

Or...

This is a quote from the Gibson Amplifier Master Service Book, page 273...

"The fuse in the GA-90 Amplifier is a type AG of three ampere rating. DO NOT USE FUSES OF HIGHER RATING."