fuse value for small transformer

[Chai]

I'm putting together a transformer in a box just for hobby stuff and I want to put a fuse on the primary.

Did I understand the values correctly? Sorry for such a basic question!

7.56 VA
Primary: 115V
Secondary: 6.3VCT @ 1.2 Amps

Primary fuse value: 7.56 / 115 = 0.066 -> ~80mA slow blow
Full secondary max: 12.6V @ 0.6A
Center tap max: 6.3V @ 1.2A

[james_s]

That sounds reasonable. If you wanted to verify, you could measure the primary current while briefly shorting across the secondary and see how much it draws, then select a fuse value that is below that by a good margin.

[Benta]

You should rate the fuse higher, otherwise you'll probably be replacing it all the time. The primary fuse is not for overcurrent protection, but rather for fire protection should something go wrong. I'd suggest 250 mA slow.

[Zero999]

I'm putting together a transformer in a box just for hobby stuff and I want to put a fuse on the primary.

Did I understand the values correctly? Sorry for such a basic question!

7.56 VA
Primary: 115V
Secondary: 6.3VCT @ 1.2 Amps

Primary fuse value: 7.56 / 115 = 0.066 -> ~80mA slow blow
Full secondary max: 12.6V @ 0.6A
Center tap max: 6.3V @ 1.2A

How about the losses in the transformer?

The primary current will be much higher than your calculations suggest.

Small transformers are notoriously inefficient. Unfortunately I couldn't find the efficiency of the transformer you're using but it will be similar to any other transformer of a similar power rating. The data sheet linked below says 69% efficiency for a 6V transformer, so assume about 70% for your transformer., so the primary power will be around 14VA, giving a primary current of just over 120mA.
http://www.farnell.com/datasheets/2603262.pdf?_ga=2.104444297.887224271.1527338544-47418993.1417808164

As Benta said, the fuse isn't to stop the transformer from being damaged, but to protect against fire and making the fuse double the nominal current is a sensible suggestion, hence 250mA. I wouldn't recommend anything less than a 200mA fuse.

Note that this transformer has a 6.3V secondary, not 12.6V!

What load is the transformer powering?  If it's a rectifier and smoothing capacitor, I hope you're aware that the maximum DC current will be around 70% of the secondary's rating.