Your unit's manual (doesn't say operating watts in from wall)
The small Variac has a 5 amp fuse, the larger a 20 amp fuse.
https://conradjohnson.com/owners-manuals/prem11man.pdf
You might want to have spare fuses available:
"Internal Fuses The Premier Eleven power transformer is protected by a fuse on the ac power line (F1, located on a chassis mount fuseholder), and by seperate fuses (located on the small pc board near the back of the amplifier) on secondary windings for the filament supply (F2, - the fuse nearest the front of the chassis), the bias supply (F3) and low voltage supplies for the bias indicators (F4 and F5). A failure of any of these fuses is a symptom of a more serious problem, and a competent service technician should be consulted. In no event should fuses be replaced with a value or type different than that originally supplied.
The correct fuse values and types are: F1: 5 amp, slow blow If configured for 100 or 120V: 3 amp, slow blow if configured for 220 or 240V. F2: 4 amp, slow blow F3, F4, and F5: 1/4 amp, fast blow"
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here's a medium size/price 15 amp version:
https://www.amazon.com/dp/B0CZ3TV6ZR/ref=sspa_dk_detail_4?sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw

