Dodgy Fuses? - Page 1
Forum section: electronics / testgear

author: slubtle
author_rank: Newbie
timestamp: January 09, 2020, 11:05:40 pm
content: Hey everyone,My next project is a DIY valve amplifier kit, so having something which can handle decent voltages and currents without killing me is an absolute imperative. I upgraded my very, very old Fluke 77 for a used Fluke 175 off trademe, and it seems in pretty good condition.The first thing I checked after it turned on was the fuses. They both appear not to have blown, but it looks like the previous owner had a wildly-out-of-spec fuse in the 440mA spot, and I wanted to make sure that:a) I was reading it correctly; andb) there isn't anything fishy about the 11A fuse tooI've already ordered a proper replacement 440mA from element14, but given the intended use of this meter is the high energy inside valve amps, I want to be 100% that I'm as safe as I can be before touching anything. I'm a newbie to electronics, but am slowly learning and taking on projects to learn as the hobby deepens. That being said, I have an immense amount to learn, so coming here with my question was intended to check with infinitely more experienced and knowledgeable folks to make sure my thinking is correct.Cheers!

author: Yansi
author_rank: Super Contributor
timestamp: January 09, 2020, 11:15:05 pm
content: There is none "high energy" anywhere within valve amps, unless you are of course poking one with kilovolts anode voltages and thousands of output watts.I wouldn't be scared to poke in a valve amp using a cheap Uni-T multimeter.When high energy is relevant, is using the meter within power distribution/industrial equipment and industrial size power inverters, where the cap banks easily store kJ of energy. (not your typical pisspoor valve amp).

author: wraper
author_rank: Unknown
timestamp: January 09, 2020, 11:20:26 pm
content: 11A fuse is proper multimeter fuse. Mechanically oversized 12A fuse is not meant to be used in multimeters.

author: Cubdriver
author_rank: Unknown
timestamp: January 09, 2020, 11:22:18 pm
content: The 11A fuse looks legit, but that 12A one certainly has no business being there. It'll be good to replace it with the proper 440mA one. <Edit to add - I hope that the gimongous 12A fuse hasn't distended the fuse clips too much - it's far bigger than the correct one will be.> That said, those fuses are unlikely to be called into action in your tube amp build as they are in play only when you're measuring current, and you're far more likely to be measuring voltage that current with what you're doing.Just be careful making your voltage measurements and you'll be fine.What kit are you building? I wish you success.-Pat

author: slubtle
author_rank: Newbie
timestamp: January 09, 2020, 11:48:29 pm
content: Quote from: Cubdriver on January 09, 2020, 11:22:18 pmThanks for confirming my suspicions!The fuse clips are definitely a wee bit warped, but I'm sure they'll bend back into place without any difficulty. And of course you're entirely right that I'll be much more likely to be testing voltages than getting into the current. I'm really just trying to factor in my own current ignorance/future stupidity. There's every chance I may do something foolish or careless, so putting as much safety in place as possible before I start work seems wise.The kit is a Tweed Deluxe (5e3) from Trinity Amps in Ontario, Canada. I can't wait to get started!Thanks again!

author: Cubdriver
author_rank: Unknown
timestamp: January 10, 2020, 12:17:21 am
content: Nice!! I built a Tweed 5F1 kit from TubeDepot a few years ago. Great fun. Post pics when you get going on it.-Pat

author: Fungus
author_rank: Super Contributor
timestamp: January 10, 2020, 07:46:39 am
content: Fuses are expensive and hard to find.It's not surprising that people shove in any old fuse when they blow one. Count yourself lucky they didn't just wrap the old fuse in a piece of tin foil (or copper wire) and put it back in.