Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: G._Hoffman on March 17, 2025, 09:38:05 pm
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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!
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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.
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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?
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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?
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See linked article for suggestion from RG Keen on heater fusing and follow that
https://www.premierguitar.com/the-immortal-amp-mods-pt-2 (https://www.premierguitar.com/the-immortal-amp-mods-pt-2)