Check my heater fuse math, please?

[G._Hoffman]

2 6L6GC's (2*.9A), 3 12AX7 (3*.3A), and relay switching stuff (.15A total, though that is on the regulated side of the 7805, but that shouldn't make a huge difference, right?). 
So:

(2*.9)+(3*.3)+.15=3.75A 

So, do I go with a 4A or 5A fuse on the center tap?  The heater winding on the PT is rated at 5A, and a quarter amp seems a pretty small margin, so I'm leaning towards 5A.

Thanks in advance!

[SEL49]

So, do I go with a 4A or 5A fuse on the center tap?

Putting a fuse on the center tap will do nothing because the tube heater current does not flow through the center tap. The center tap only provides a ground reference to reduce heater hum.

[G._Hoffman]

So, do I go with a 4A or 5A fuse on the center tap?

Putting a fuse on the center tap will do nothing because the tube heater current does not flow through the center tap. The center tap only provides a ground reference to reduce heater hum.

Doh!
I knew that, and just forgot somehow.
So, 2.5A on each line?

[SEL49]

So, 2.5A on each line?

No. the entire 3.75A will be flowing in each line. I would use at least a 6A fuse. But really, why do you even want to fuse the filaments?

[tubeswell]

See linked article for suggestion from RG Keen on heater fusing and follow that


https://www.premierguitar.com/the-immortal-amp-mods-pt-2