Fuse Holders

mlucitt

Veteran and General Yakker
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Jun 24, 2011
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Jacksonville, FL
#1
To All,
I was disassembling a PL700 recently ("tear down" and "gutting" are such strong words). I noticed a broken fuse holder and examined the item very carefully for the first time. These are the well-known Buss devices. Cooper Industries was an American worldwide electrical products manufacturer headquartered in Houston, Texas. Founded in 1833, the company had seven operating divisions including Bussmann electrical and electronic fuses. Doing research, it appears Cooper was acquired by Eaton in 2012. So these are now Eaton Bussmann fuse holders.
Mine are marked "HJM" which is an obsolete P/N. Interestingly, all five of these fuse holders are only rated at 5A and 125V and the length supports the fast-acting AGX length fuse at 1/4" x 1". The replacement is P/N HKP, a 15A 250V part designed for the AGC 1/4" x 1 1/4" length fuses. Although you can cram an AGC fuse in an AGX fuse holder, this is a lot of spring pressure because the inner plunger is too long for the AGC fuse.
Of course, the newer fuse holders have plastic securing nuts, so save the metal nuts from your old fuse holders. The metal nuts are an optional part, but I could not find a P/N. HKP is found at Mouser by P/N 504-HKP at $5.74. The black washer is Mouser P/N 504-BK/9732.
The HKP fuse holder also comes with many P/N descriptors (from Mouser):
HKP-H-R
HKP-CC-R
HKP-W-R
HKP-BBHH-R
I know the "R" on the end stands for RoHS compliant, I cannot find what any of the other descriptors stand for.
As for the fuses, Watts Abundant pointed out that 125V AGC fuses are only rated for 10A, then the voltage decreases to 32V. That's OK for the Rails but not the Line. The better solution for a Line fuse is the fast-acting ABC fuse, but they are ceramic, not glass, for the higher voltage/current flashover.
I will use the new HKP fuse holder for the line fuse because it is rated at 15A. I have not measured the individual rail supplies current draw, but it might be close to 5A at full power levels (and DC current is a different flavor than AC current, no?). Possibly, Phase Linear used a 5A Buss fuse holder to save money? Not sure.
Thoughts?
Buss 2.jpg
 

Skywavebe

Chief Journeyman
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Jun 13, 2010
Messages
725
Location
Bensenville, IL
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Work too much
#2
Use what size is logical to use for the application. You can upgrade on the fuse holder but assuming proper wire, soldering and all that including broad enough PCB traces, the fuse holder is not going to limit current too much. The greatest draw of a amp besides full power output is when you turn them on. At T=0 the current inrush to charge the caps is pretty high but that with good caps the duration is short. This is why transmitters use a step start system where the power supply comes on with large resistors in series then once the supply is measured to be OK- as in no shorts a relay closes across the resistors taking them out of the picture. This may not be needed with consumer amps but then the diodes they use are sufficient for the surge they are going to have to handle.
 

Skywavebe

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Messages
725
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Bensenville, IL
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Work too much
#3
Download the data sheet and then all that additional letter are explained. If a plastic nut is placed on a plastic body there really is no need for a metal nut plus you need to order a bag of 100. This is just an amp and the plastic threads are the weak part.
 

mlucitt

Veteran and General Yakker
Joined
Jun 24, 2011
Messages
3,339
Location
Jacksonville, FL
#4
Sam, thanks I found a data sheet for the newer 30 Amp Eaton Bussman fuse holder, it is posted here. My initial concern was not how much current the original HJM fuse holder consumed, it was more about how illogical it is to use a 10 Amp fuse in a fuse holder that is only labeled/rated for 5 Amps.

Also, the fuse holder is a hard plastic almost like Bakelite and has not changed over the years, but the new plastic nut is soft like polyethylene. This is why I re-use the metal nut.
 

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Rickyboy

New Around These Parts
Joined
Nov 7, 2020
Messages
19
#5
Are all PL fuse holders the half twist type? I have them in a customer’s 700B , but i have threaded units in my 700/2 ....
 

Skywavebe

Chief Journeyman
Joined
Jun 13, 2010
Messages
725
Location
Bensenville, IL
Tagline
Work too much
#6
As long as a fuse holder keep a fuse in place it does not matter what kind of retention is used. After all a fuse is just a link like safety device to blow if a 200% current draw is had from the fuse that is in there. I have stock of both types here but then I do not work on PL amps as that is the heavy current stuff.
 
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