Littlefuse 357 Fuse Block - Polk 7B

Gardenstater

Before I take the plunge and tear into this by removing all the hotmelt glue and drilling out the rivet etc., I'm wondering if anyone can tell me what I will find as far as how Polk attached the wires to the fuse block. You can see from the picture that Littlefuse didn't provide a means for soldering. I'm a bit apprehensive about what I will find and whether or not I will be able to desolder and solder in my Cardas Litz 11.5awg wire. Looks like just a rounded copper rivet head on the inside without any faston tab or anything! I'm hoping that the ones that Polk got from Littlefuse have something different on the inside, for soldering.

https://www.ebay.com/itm/Littelfuse-357-Fuse-Block-1-Pole/331919720511?_trkparms=aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=225074&meid=af5b9c07f2d24073a0076a10bdd5ccb0&pid=100005&rk=2&rkt=12&mehot=pf&sd=331615731551&itm=331919720511&pmt=1&noa=0&pg=2047675&algv=SimplAMLv5PairwiseWebWithBBEV2bDemotion&_trksid=p2047675.c100005.m1851

pitdogg2

Solder tabs or maybe fast connect on the tabs. See the holes look covered in solder.
My take ditch the fuse wire direct

Gardenstater

Littlefuse doesn't make the 357 anymore so I found this picture on eBay *but* I'm thinking to myself that Polk may have ordered ones that have fastons on the inside, underneath that copper rivet head. Let's put it this way......really hoping! Those outside tabs were never used by Polk for making the connections. Woulda looked super crappy to have wires showing on the outside.

Gardenstater

Also, my plan is to try replacing the fuses with some 1/4" dia., 0.035" wall thickness 4N copper tubes and if I hear an improvement over the fuse, I may eventually do away with the fuse blocks but *only* when I have a spare pair of Danish Peerless. I heard a distinct improvement for the Danish vs the USA ones in my testing. The Danish ones aren't rare but they are not exactly readily available.

stevep

I don't know if they were all like this but you can see how the wire is soldered to or into the backside of the rivets holding the fuse clips.



To me this seems like a case for not replacing like with like. It may be easy to see the condition of the fuse but I'd be happy, if I was keeping the fuses, using a panel mount fuse holder and pulling the fuse to check it if the tweeters stopped.

Gardenstater

@stevep Yeah thanks I saw your picture before and I wasn't able to determine how the wires are connected to the rivets. Isn't it all gooped up with some adhesive? Not really clear or sure about what I'm seeing there.

It has crossed my mind that Polk may have simply drilled a shallow hole into the rivet heads and used that as a soldering point. I wonder how much heat the thermoplastic material of which the fuse block is made can take. I don't think I see a solder tab or faston there so do you think that is what they did?

Thanks.

PS: That type of panel mount fuse holder has crossed my mind but I'm uncertain if there is as much quality to the contact. Springs making contact has never floated my boat. Maybe it's a lifetime of having to smack flashlights to get them to light etc.

stevep

I had to dig to find that picture, don't know who to attribute it to but I found it in one F1Nut's posts.

They make fuse holders in various levels of quality, I saw some silver plated "audiophile" ones but tarnishing over time doesn't sound like a good idea to me.

mhardy6647

dude! It's a fuse holder.
I can mail you one if you really, really want one. I can send some wire too.
Not sendin' a soldering iron, though.

Gardenstater

I found a couple of vintage Littlefuse 357 fuse blocks on eBay and bought 'em. Thanks though for your kind offer. This way I can drill them out and solder the Cardas Litz into the copper rivets and not have to risk my other ones on an uncertain process of desoldering and then re-soldering a copper rivet head that is right smack against a thermoplastic resin of unknown melting point. Thanks for tolerating all my silliness

audioluvr

I'd just eliminate it and keep your foot off the skinny pedal

Gardenstater

And where's the fun in that......j/k thanks!

Gardenstater

Surprise. Turns out the "copper" rivets that hold the fuse clips to the fuse block, which is what Polk apparently soldered the tweeter supply wires to, are ACTUALLY copper plated steel. I'm sure it's still solderable, I'm just not thrilled to discover this. When I was punching the head (that does not sound good) I could tell that it was a hard metal and not brass or copper. Then I checked it with a neodynium magnet and sure enough. Steel.

Gardenstater

Turns out it is doable but after doing only one I need a drink. Without a machinist's spot drill, drilling these rounded steel heads at all on center is nigh onto impossible. Whatever you do don't try a standard 1/16" drill bit because it will skate all over the place. Final size needed to be 0.080" for the 11.5 Cardas Litz.

mhardy6647

I'm not quite sure what you're trying to accomplish -- bur it has anything to do with the "quality" of the fuse's physical connection in the circuit, wouldn't it be better to solder the fuse in-line? One would otherwise always be at the mercy of the cheezy little plated metal spring clips that hold the fuse.

audioluvr

Or have the copper wire run wild through the fuse holder hole, solder the hole shut then your fuse is connected directly to the wire with the holder clips keeping tension. Then you can put in one of these

https://images.app.goo.gl/eYp3z7iYpAHgKo179

mhardy6647

audioluvr wrote: »

Or have the copper wire run wild through the fuse holder hole, solder the hole shut then your fuse is connected directly to the wire with the holder clips keeping tension. Then you can put in one of these

https://images.app.goo.gl/eYp3z7iYpAHgKo179

But, but... the connectors on that thing ain't even copper!
Think of the galvanic current that's gonna flow!

Gardenstater

Well that's a point I hadn't thought of, the galvanic corrosion. Did anybody bring this up with Matthew Polk because this is the exact same way they did it? I may do another pair of fuse blocks where I bring the wires up through the XO cup at the ends of the fuse blocks so that they are not all that visible and solder them directly to the brass solder fittings. I figured I went so far as to purchase a pair of fuse blocks, and also none of ya geniuses told me that I was wrong about the rivets being copper . Nobody told me hey knucklehead they are not solid copper they are copper plated steel! No worries I will probably end up pulling my existing ones out and doing as above because I really don't like the steel although lets face it the rivet is a pretty large gauge of steel and the current is going through about 0.100" long section of steel after also passing through brass fuse clips and a fuse. The DC resistance of that steel is pretty miniscule if you want to calculate it and get back with the results.

vmaxer

Just use a small copper rod.

Gardenstater

mhardy6647 wrote: »

I'm not quite sure what you're trying to accomplish -- bur it has anything to do with the "quality" of the fuse's physical connection in the circuit, wouldn't it be better to solder the fuse in-line? One would otherwise always be at the mercy of the cheezy little plated metal spring clips that hold the fuse.

The "cheezy" spring clips actually wrap around the fuse end caps and have a pretty large amount of spring tension and contact area. I use silver platelet grease also. Just a trace amount is all you want. Mapleshade Silclear.

pitdogg2

galvanic current that's gonna flow!

Oh man I think I just melted....

Gardenstater

vmaxer wrote: »

Just use a small copper rod.

Exactly. I want to experiment with seeing how the sound improves if at all, if I substitute a 1/4" piece of 4N copper tubing for each of the fuses. I may even do a double blind test with a couple of my audio buddies.

F1nut

Do you get headaches from over thinking everything?

Gardenstater

Ha! Like I said I'll quit thinking when I'm dead. A lot of those amplifiers and speaker systems you guys love so much had a lot of "over thinking" involved in their development I'll wager.

audioluvr

OR like someone said earlier here, just eliminate the fuse block doodad(technical term)

Gardenstater

Ah yeah man and I said it was a good suggestion. However, before its time because I do not have a spare pair of Danish Peerless on hand should my 40 year old amplifier which has never been serviced decide to crap out square waves or whatever might go wrong, and fry the tweeters. If the 4N copper tubes sound better that's a pretty good indication that direct wiring with no fuse block will sound better still. One step at a time. It's gettin' better and better.

I will say that when I was young and only had a Technics SA500 55W receiver powering these I did on a few occasions blow the 1amp fast blow fuses. Who knows, maybe it saved the tweeters. I know of at least one member here who bypassed his fuses since I joined in Nov and totally regretted it.

audioluvr

Oh sorry I didn't catch you running them with unmodded vintage power. Best to stick with a fuse

mhardy6647

Gardenstater wrote: »

mhardy6647 wrote: »

I'm not quite sure what you're trying to accomplish -- bur it has anything to do with the "quality" of the fuse's physical connection in the circuit, wouldn't it be better to solder the fuse in-line? One would otherwise always be at the mercy of the cheezy little plated metal spring clips that hold the fuse.

The "cheezy" spring clips actually wrap around the fuse end caps and have a pretty large amount of spring tension and contact area. I use silver platelet grease also. Just a trace amount is all you want. Mapleshade Silclear.

So -- out of academic curiosity (or maybe just masochism) -- what are the materials of construction of the spring clips?

Gardenstater

What's your point Doc? They make them out of an alloy of brass that has a spring temper, so that it is functional for a spring contact. It falls under the category of a necessary evil. I don't know of any mfg. who uses copper for spring contacts, either fuse holders or fastons or banana plugs. Do you?

I am not at this time ready to solder wires directly to a fuse but it might be an interestingly zany experiment to try some time in the future. Big PIA if the fuse has to be replaced though

Gardenstater

Doc ideally every conductor in any audio signal path should be UPOCC copper or even silver but you have to draw the line somewhere with practicality in mind. I'll be happy enough to see how the Cardas Tellurium Copper Binding Posts and the 11.5 Cardas do as far as improvements. Each change is a stepping stone. Baby steps are the way I'm going and I enjoy seeing the incremental improvement that each gives and weighing which one had the most effect. Isn't that what the hobby is about for most of us?

mhardy6647

Gardenstater wrote: »

...
I am not at this time ready to solder wires directly to a fuse but it might be an interestingly zany experiment to try some time in the future. Big PIA if the fuse has to be replaced though

Why not?

BlueFox

Has anyone ever soldered wire to a fuse? It seems the soldering iron heat would easily melt/blow the fuse.