Fast acting fuses? QRX-7001

N8Nagel

AK Subscriber
Subscriber
Hi all

so I have a QRX-7001 all apart at the moment, unfortunately the fuse lamps I bought don't fit (LEDs, too long) and also while attempting to make everything work I managed to blow F5. At least i got the "digital indicator" lighting up correctly, and I completely desoldered and resoldered each of the fuse lamp clips so hopefully if I can find LEDs that fit this is a permanent fix for flaky dial lamps.

While looking for the board on which F5 resides (it'd be nice if they showed you in the manual, for future reference it is a daughter card to the board with the speaker fuses) I noticed that two of the speaker fuses had apparently been replaced at some point in time. The other fuses all have a red dot on them. I do remember seeing mention that those were "fast acting" fuses, are those just normal non-slow-blow fuses or are they quicker acting than normal? If the latter, what do I ask for to replace them, or tell if the replacements installed fit those qualifications?

thanks!
 
Don't know anything about red dots. On one or both end caps of the fuse usually is the type (often three characters, AGC, MDL, etc.) voltage rating, and current rating.

Very generally speaking, a straight piece of wire is some version of fast blow. Anything other than that is likely some version of slow (er) blow.
 
Well I'm going to have to get some... the two that were replaced are labeled 1.6A whereas the 6 original looking ones with the red dots are all 5A

they are 5x20mm with no type indication but what's her face has Amazon Prime so I'm just going to ask her to order me a pack of Bussmann GMA-5A unless someone has a better idea (light fuse is same size and also 5A)
 
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rating is 5A for speaker fuses and 5A for lighting fuse

I blew the lighting fuse probably because of not being careful placing the dial light holder (uninstalled) for testing

I found the wrong fuses in two of eight positions for the speaker fuses (too low amperage, but if I buy new ones I would like to get the right ones) I *suspect* that these are high speed/very fast acting/semiconductor protection/whatever you want to call them fuses, but I am having a difficult time finding any in a 5x20mm format. Only one I've found - and I've been searching since I posted - is Littelfuse 2301500002 which is a ceramic fuse and apparently only available from Digi-Key, guess that means I might as well see if they carry the protection relay for my Luxman which I also need.

I also cannot install the fuse *lamps* that I bought because they do not fit in the dial light holder. dgwojo threw one of his "cool white" fuse lamps in the package as a sample and that fits fine, the "warm white" fit in the meter positions but not in the PITA dial light positions which is where I really wanted to convert to LED to prevent problems. Unfortunately one of the stock fuse lamps is starting to fall apart so that's a non starter too...

three separate problems...
 
You really should download the manual from Electrotanya if you haven't already done so ...

http://elektrotanya.com/sansui_qrx-7001.pdf/download.html

qrx7001-fuses.jpg


Those are all fast acting ... the back panel fuse is a standard 7a ...

And ya, I've heard some of the LED fuse lights won't fit in tighter lamp boxes. Try again I guess, or go with standard 8v lamps. And no, a standard fuse doesn't have the right filament to replace a lamp.
 
I have that manual and I also found the owner's manual at HFE

the fuses I'm talking about that I think may be special high-speed are on F-2427. I need fuses for F02 and F04 on that board as well as F05 on F-2456, which is the fuse for the lighting. Those fuses don't look the same although they are the same size and rating.

F05 on F-2456 (lighting) is marked TOYO on one end and 5A on the other.

the fuses F01-F08 (other than F02 and F04 which are obviously incorrect) on F-2427 are marked with a red dot on the glass and TOYO SH on one end and 250V5A on the other

this makes me think that there's something special about the fuses on F-2427, along with the blurb from the owner's manual, pg. 16

"This set offers double protection for the important power transistors and your speakers. One, an electronic relay-equipped protection circuit; two, special quick-acting fuses that instantly blow should an abormal condition occur inside the set or at the speaker terminals." yadda yadda and so on and so forth.

I'm wondering if quick-acting is not what we call "fast acting" today but "very fast acting" "semiconductor protection" or "high speed"...

Oddly, the manual on Elektrotanya calls all the fuses on F-2427 out as 4A, 250V quick-acting, P/N 0433630 however both the silkscreening on my F-2427 and 6 of the 8 fuses are in fact 5A.

I could not find any info on F-2456 other than on the schematic. i had to just poke around the chassis to even find the @#$% thing. If anyone else is fighting one of these, F-2456 is accessed by removing the black metal cover on the right rear of the chassis (as looking at it from the top with the dial towards you.) It is a daughter card to F-2427 and is opposite F-2458 which *is* labeled on the diagram of how to locate stuff.
 
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Wonder if that might be a 220v vs 120v kinda thing?

Hopefully somebody here can pop their top and let you know what they find. In the meantime, I'd go conservative - install 5a quick acting where the schematic shows 7a, and the 1a where you found the 1.6a

And ya, I saw the 4a fuses listed in the manual as an "accessory" ... haven't a clue what that's all about. That's just the inscrutable ones being ... inscrutable. ;-}

Maybe time to take a break till you figure out what's what.
 
I think I have found a semi-authoratative explanation

http://www.woodang.net/qafuses.htm

"Quick Acting Fuses (glass)
For protection of Transistors etc.
These Fuses are extremely quick and about
10 times faster than Standard Fast Blow Fuse.
Do not replace with Standard Fast Fuse.
If so, you loose the protection function"

I might have even landed on that page before looking for something else

so i'll just order some of the red-dot Toyo fuses for now and if they ever become unavailable I would assume that the Littelfuse I mentioned above would be an acceptable replacement.

http://www.littelfuse.com/~/media/f...urces/documents/data sheets/230_lf_012006.pdf

The 1.6A fuses are just weird, they are in holders that have "5A" silkscreened behind them, so that's why I'm itching to replace them. Guess nobody ever cranked this one (at least not since blowing the fuses <G>)

so I'll use a 5A regular fast blow fuse for the lamps, and the 5A red dot fuses for the speakers

maybe the 1.6A would be appropriate for the lamps after I get some LEDs that fit
 
Now that I think about it maybe whoever put those 1.6A fuses in might have known what they were doing... iirc aren't those the fuses you pop to adjust bias which is normally in the mA range? and let's say you had a 15A current flowing over that fuse, that's 3X the rating of the QA fuse but almost 10X the rating of the regular fuses so maybe tine to blow is in the ballpark? I've only checked offset but that was darn good so presumably someone did at least a little adjustment on this and didn't bone it up...
 
Now that I think about it maybe whoever put those 1.6A fuses in might have known what they were doing... iirc aren't those the fuses you pop to adjust bias which is normally in the mA range? and let's say you had a 15A current flowing over that fuse, that's 3X the rating of the QA fuse but almost 10X the rating of the regular fuses so maybe tine to blow is in the ballpark? I've only checked offset but that was darn good so presumably someone did at least a little adjustment on this and didn't bone it up...

Well, I've been up all night due to factors outside my control... guy at the website I posted earlier got back to me, he still has the Toyo 5A "red dot" fuses so I figure I can't go wrong with OEM :)

I'll get some regular 5A fast blows as well and use one of those in the light fuse spot

now all I need is to get my lights squared away and I can hopefully just confirm the adjustments that I can and use this thing!
 
It's rather a faint hope expecting fuses to protect semiconductors, but at least it's nice to make efforts to get the fuses that might at least give some chance. :)

skippy's link (when you select) refers to "250VAC, 5A · Super-Quick-Acting FF" fuse

Mouser P/No 693-0034.0908

Which would (at a price) provide maximum protection. ;)
 
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It's rather a faint hope expecting fuses to protect semiconductors, but at least it's nice to make efforts to get the fuses that might at least give some chance. :)

skippy's link (when you select) refers to "250VAC, 5A · Super-Quick-Acting FF" fuse

Mouser P/No 693-0034.0908

Which would (at a price) provide maximum protection. ;)

Well, that's (slightly) cheaper than the one I found at Digi-Key...
 
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