I had a Phase 400 many years ago. I used to blow the 5 amp agx rail fuses so I stocked up on both the 5 and the 8 amp versions. I may still have a few. I got rid of the amp in '99 when I "re-designed" by main audio system for more efficient speakers and "distributed" amps. The Phase 400 is basically an under-engineered amp. It requires and external fan and has a very "sharp" sound. I had mine from ''73 to '99 before I "saw the light" and switched to more efficient speakers and MOS-FET amps (with speaker protection). A buddy of mine STILL uses a Phase 400 for his twin subs.
Excellent lesson Tony. Glad you're OK. If there's one thing I've learned from all my years engineering, it's that attention to detail may not matter much at micro power levels, but it all goes horribly wrong once large power is applied (and that usually happens exponentially). Respect for the "potential" at hand is a lifesaver. Keep up the great work, repairing and teaching.
I’ve never before heard anyone explain the mechanism by which (or the physics of how) a mis-rated fuse blows. I’ll never forget how our fork-lift mechanic found out that his fuses needed to be rated for 32V, not 125V or 250V, it seems the current rating was much lower in the fuses intended for AC circuits. The 125/250V fuses would blow instantly when power was supplied; only the 32V rated fuses would hold up in the circuit.
Actually just happened to me last night. I bought a Sansui TA300, did the usual cleaning, deox and scope readings to check power, adjusted the bias. Was cranking along pushing the volume a bit, then poof. Nothing. Yep 32 volt car fuse across the main power. Took out an output transistor. Now in elbow deep swapping all outputs and recapping as one of the main caps was down to 60-70% of rating. It was sounding really nice, so I’m going to go through all the boards to recap.
Glad you covered this as I was in a heated argument years ago with someone who said I was wrong and he insisted to tell everyone "a fuse is a fuse, does not matter voltage rating" and I just walked away :)
A friend once asked me, what is Impedance? I replied, You got 6 months? He said What?.. I said, after you learn DC resistance, then trigonometry, then AC circuits, Capacitance, Inductance, then vector mathematics and then you can understand Impedance.
Enjoy all your videos .In the words of my General Foreman Electrician on a commercial building site back in the 80's."Find the short first then replace the fuse"
I loved hearing about the X-Ray equipment. If my head wasn't already full of magic from computer hardware repair, general electronic repair and network consulting I'd take some time to study it. But I'm 57 and I doubt I have enough years left before I retire to learn it to a really useful level. I'll stick to valve (tube) radio repair as a hobby for additional head scratching. 😄
Hi Tony I like your lanyard 😃 and the mic works great with it. WOW that’s a crazy story! Can’t wait for your next series of vids….thanks for the fun 👍👍
Very good explanation on fuse characteristics, Tony! In such high-voltage and -power circuits as in your X-ray situation right fuse type is very important. Many other instances fuses are -well in my opinion- mostly used to not start a fire.. Many fuses used in "consumer equipment" are not very precise... If they were, the cost would be too high (like your example from the X-ray episode) Very good!
LOL, Tony, I saw that blue flash come out of one of my old GE DXD 350s when the potentiometer shorted between stations while my tech took an exoposure years ago. Just did a tube recal on a CPI generator this morning when the generator lost its cal data. I have learned a lot from my service engineers over the years and you too. Thanks for the great lesson.
I haven't seen a DXD350 in over 20 years! We are a CPI dealer. If it is a CPI Indico, they have a known issue where they will start losing config data. Re-programming them only fixes it temporarily. CPI has an upgraded CPU board (under the flip-up lid) that will correct the problem. I have not seen it happen too much on the CMP series. They seem to have a better memory ;)
@@xraytonyb Tony, I have 2 DXD 350s in my storage barn that I bought new in 1986. We replaced them with 2 CPI Indicos and one loses config data about every 3 months so I have my restore and recal technique down to 22 minutes using my cheat sheet so I remember each step. I think James from CPI told my service engineer about the motherboard. He is just too busy (Merry X-Ray) to schedule time for us due to staff shortage as you are well aware of.
Intentionally or not, you used the term impedance very well. I guess for this though experiment an intact fuse should be modelled as a resistor and an (tiny) inductor connected in series. In this state it has both low resistance and low reactance, hence low *impedance*. The open fuse on the other hand would be a very high value resistor in parallel with a really tiny capacitor. A crucial part from a theoretical stand point is the high DC resistance, no doubt: A high reactance alone in parallel with a low value resistance would not suffice in case there is DC applied to the fuse. For low frequency AC the reactance of the tiny capacitor is huge, so the alternating current through this "parasitic" capacitor is about zero. If it was a better capacitor, we would have a problem though. So both the resistance and the reactance are kind of important... => Calling it high *impedance* seems to make sense to me, even if it doesn't specifically mention both aspects. (The real power dissipation across the mainly resistive filament causes the fuse to blow, so an intact filament-type fuse can't have zero resistance, not even in theory, but the reactance could be 0.)
Some day when you've nothing to do, load up a glass fuse & watch how the fusing wire dances around inside the glass. Especially when you get near the amperage limit. I often wondered what the non-linear I squared R loss (thru fuse) affect is to the amp. And then we put 10ga speaker wires after a fuse that is ~30ga "equivalent". Great vid. Thank you.
I have worked on that exact model amp and I owned that same one too and I still have in my fuse stock that 8 amp fuse and also that replacement fuse holder !
I was talking to my apprentice about this very subject (AGX vs. AGC) yesterday. You have a parts-eating floor too? How is that these floors find their way into so many shops???🤣
Huh! I never knew that, thanks for the detailed explanation. Can you do a video in even more detail about fuses? Like why is the element shaped differently ins some fuses or what makes a fuse fast-fast and what are those resistors for in fuses.
And don't forget, fuses get old. Just like people they degrade as they age. On normal glass fuses every time you energize and de-energize a circuit the fuse element heats up and cools down / expands and contracts. This causes fatigue in the metal zinc fuse element. Over time this "fuse fatigue" causes the current carrying capacity of the fuse to decrease and eventually blow. Point being fuses do blow for no apparent reason. I took notice of how many fuses I stock in different types and current ratings when I did inventory last year. 393 different type and current rating. What's scary is I still get caught not having the correct fuse in stock from time to time. Everything from tiny Pico fuses to BAN/FNQ size fuses, leaded and non leaded, numerous different time rating fast and slow blow, different voltage ratings, vibration resistant, high heat rated. It's crazy how many specialty fuses there are.
Replace the fuses with circuit breakers. Aircraft use CB's because fuses are notorious for half-blowing. The filament can sometimes melt a little bit, so it is weakened.
I'm actually looking for a fuse that doesn't cost an arm and a leg. It has to withstand 125A and 60V and break quickly. I've seen that most people and even factory equipment use 32V/125A standard fuses and somehow that doesn't sit right with me. Those batteries have a LOT of power in them. Then there are the "switchable" fuses that are used in marine environments, but those are also rated for 32V. I was considering putting that for convenience but that also sounds wrong even though that's what other people use.
:) possibly even more. Just looking for the right affordable fuse for the application. My idea now is to use a general-purpose (gG) fuse that's rated for the voltage but has lower amps (eg 60 instead of 125A). Since the system will rarely run at 100%, I'm fine if it blows after 15 min at full load.
Tony talking about fuses, do you know the difference between a fuse and a fuze? A fuse is used for electrical protection. A fuze is used for lighting an explosive like a cannon or Dynamite. A lot of people get confused between the two.
Yes, there is. The sound stage of that generator exploding was incredible! Now that the cables have been properly burned in, it should sound even better ;)
A topic that's been on my mind, one of my VTL mb-300 tube amps popped a B+ fuse while I was trying to bias up new tubes, and while I was digging for replacement, I wondered... these are 250v fuses, these amps run like 550v of B+, shouldn't they have higher voltage fuses?
N’at = and that (From the language of those living in or near Pittsburgh, Pennsylvania) An oft-used extender to just about any sentence. “We were watching the Pirates and drinking beer, n’at.” Of course, like yinz, "and that" isn't even a particularly common phrase in standard English, but generally n'at is a more or less meaningless casual phrase to tag on to the end of a sentence, like "and whatnot." You also might see it as a bumper sticker, spelled "n@."
Fuses, boy that can be a long conversation. Try ordering some from mouser. Grab your ankles. Get the right fuse. Remember they not only protect the circuit, they also help prevent fires. Watch out for Amazon fuses. You don’t want a 2A fuse that takes 8 or more amps to blow. Can’t be skimpy.
If you buy Amazon fuses, I highly recommend testing ALL of them. Once they have (hopefully) all blown, then go ahead and order more from somewhere else. Always invite the neighborhood kids over to watch you blow stuff up. Kids love explosions! Discharging a really big capacitor with a screwdriver always makes for a great start.
I worked on 4 of these amps for a local bar in Corpus Christi called barton st pub the amps had output transistors that I crossed to mj15024 don’t quote me but peavey proprietary number was 70473180 or 70483180 nte 388 nte 68 not sure as for fuses I don’t remember I may have swapped the fuse holders to agc very robust transformers.
