Fuse holder, Fuse Clips and Wiring

[makinrose]

The TUT series recommends a lot more fusing than most builders use for MI tube amps but it make sense to me to provide the maximum protection possible to the transformers and thus also protecting  the owner from expensive replacements. Up until now I've been using two panel mounted fuse holders (one for the mains and on on the HT). 

I've been trying to work out the best method or part to use to mount fuse clips/holder to the eyelet boards so I can add more fusing.  What method do you guys use?  Any recommended fuse holder/clips/fuse blocks that are easy to mount on a eyelet board?   Is it preferable to still have some of the fuses be panel mounted or better to have them all be internal.  Thanks!

[K O'Connor]

Hi Guys

ALL fuses should be internal.

Generally, external fuses make it too easy for the equipment operator to install the wrong size fuse and cause more damage or even a fire, after the fuse has blown for some reason. people will do desperate things in unexpected circumstances, like wrapping the dead fuse in foil and re-inserting it. In older equipment you might find an internal fuse wired in series with the panel fuse as a means to provide protection from the user

TUT3 refers to Keystone 4245 fuse clips, which hold a 1.25" x 0.25" fuse and mounts in four eyelets. Takes up a lot of space, but that is what we started with in the hand-wired amps. This is a unitised piece with a narrow fibre-glass strip with two fuse clips on it - a bit more rigid than using the bulk clips, although you can do that easily since your eyelet boards are likely glass-epoxy; mine were Teflon, so the added rigidity for the fuses was welcome.

To some extent, any PCB-mountable fuse clip can be used in eyelets. Keystone has bulk clips to fit 1/4" fuses and for 5mm:
1/4" dia - 3514, preferred, 3529, 3515, 3516P
5mm dia - 3517, 3518P
The preferred part has 0.25" long tabs to go into the eyelets, where everything else is 0.14".

Depending on how many fuses you intend to install, it might be better to buy unitised fuse holders and solder them to eyelets or to printed traces just for this part of the amp. The latter approach opens up more choices of fuse and fuse holder. There are also fuse blocks, which are rigid material with a number of fuse positions where the clip has a wire solder lug.

I've built amps where there were eleven fuse holders, which makes it very appealing to use 5x20mm fuses and PCBs. The 5x20mm is universal. Even most US builders use this size now instead of the 1.25" x 0.25" types.

[makinrose]

Kevin,

That's very helpful indeed. I appreciate the info. I really think I need to move over to that. I've seen more than few amps where the owner thought "it just needs a bigger fuse" and has caused real damage. Heck I've seen people put a piece of foil in there. I guess lots of people really don't know what a fuse does.

The clips I initially found had very short pins so I was having trouble mounting them. With .25" pins I should be much better off. I also agree that the 5x20mm are way to go. As crazy as it sounds I'm rather excited to improve the fusing!