Fuse Protection of Vintage Transformers

[David Root]

Recommended in another thread by someone who lost an old Fender OT.

Fuse the PT CT to ground, 0.5A slo-blo for two 6L6GCs.
Fuse the OT CT to B+, 0.1A FB for two 6L6GCs.

Given that quiescent current can be 35mA each tube, and full bore output much higher than that, I upped the OT fuse to 0.2A.

Is that enough? I will also put an inrush limiter in the mains line.

Below is a pic of how I'm doing it. This is a '67 Bassman set of iron, '70s 50W ODS in a BFPR shassis.

[Structo]

I wonder why amp makers have gotten away from doing just that?

I'm not talking about the mass produced disposable pcb amps that aren't made to repair but the quality custom built or higher end ones.

Or even diodes on the power tubes to protect things.

[VacuumVoodoo]

I wonder why amp makers have gotten away from doing just that?

Because of ignorance and/or nonchalance? Had they asked an expert in electrical safety to just "have a look and see" at their product per relevant IEC standard then......
Mind you, this does not apply to only small builders, even some major names are lost in the woods when it comes to proper placement and dimensioning of fuses and following norms.

[tubeswell]

Recommended in another thread by someone who lost an old Fender OT.

Fuse the PT CT to ground, 0.5A slo-blo for two 6L6GCs.
Fuse the OT CT to B+, 0.1A FB for two 6L6GCs.

Given that quiescent current can be 35mA each tube, and full bore output much higher than that, I upped the OT fuse to 0.2A.

Is that enough? .

200mA Slo Blo is the standard Marshall OT protection fuse IIRC