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Post by mr_sooty on Apr 27, 2009 23:40:56 GMT -5
I have had a new Fender 65 Deluxe Reverb Reissue for about 5 months. In that time it has blown 3 fuses. It's not like it happens all the time, just every now and then.
It always seems to happen at power up (never while playing or anything), and it seems to be when I forget to check where the power switch is set to before I plug it in (the switches are on the back). If I follow the correct procedure of plug in -> power switch on -> wait -> standby off, it seems to be OK.
I'm in New Zealand on 240v mains. The fuses recommended (and included stock) are F1A, 1 Amp fast blow fuses.
I've had a Peavey Classic 50 for ten years, and it's never blown a fuse, despite my sometimes slack start up routine.
Two questions:
1: Should I be concerned with this semi regular fuse blowing?
2: Would it be a really bad idea to try a slow blow fuse in there?
By the way, I've already replaced the recitfier tube, I hear a bad rectifier can cause fuse blowing. This happened with both rectifiers.
Thanks.
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Post by sumgai on Apr 28, 2009 2:23:28 GMT -5
sooty, That fuse should be a slow blow, not fast blow. If the back panel label says fast blow, it's wrong, pure and simple. The reasoning is, fast blow fuses can't handle the sudden inrush of current when the amp is first turned on. That large load is caused by the tube's heaters (the filaments) - they draw a helluva lot of current during the first few seconds, and a normal fuse (fast blow) decides that something is wrong, and protects the amp/user/house/whatever. Small consolation for the person who was about to play.....  Enter the slow blow fuse. It is specifically designed to handle an overload for a short time, without blowing, and without shortening its life - it'll last years, if it doesn't blow for other reasons. And yet, it's rating (1 amp in your case) will protect the circuit, and the surrounding environment, should a true fault occur. Just what the doctor ordered.  Yes, you could just use a 2.5 amp (or greater) fast blow fuse, but then the amp would not be protected to the design specification, and that's what's known in the business as bad ju-ju. Just use a 1 amp slow blow fuse, and be done with it. HTH sumgai |
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Post by mr_sooty on Apr 28, 2009 3:26:06 GMT -5
Cool, thanks for that. It's wierd that the manual suggests fast blow though. I trust that you know what you're talking about, I have had plenty of good advice from you in the past, but I might just wait for confirmation from more experts. If I get 2 or three of you guys saying this, I'll make the switch.
Cheers.
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Post by mr_sooty on Apr 28, 2009 3:38:20 GMT -5
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Post by ChrisK on Apr 28, 2009 18:37:40 GMT -5
I'm an expert 2; I recognize mistakes when I make them again. sumgai is correct in that the heater ( heat infers power, doesn't it?) does draw significantly more power during warm-up (after all, uh, heat is what warms up the heater). Ah yes, the proper switch sequencing..... sumgai didn't mention that the DC (plate) power supply is a capacitor input topology. This likely occurred since such topics oft cause aneurysms in those that slept thru math (or engineering) classes. These have a huge inrush current as the capacitor is essentially a direct short (well a few Ohms) when not fully charged. These also have large current rectification spikes over narrow phase conduction angles, which requires a larger fuse than an inductor (choke) input topology. This is limited by TH1 which is an NTC thermistor (Negative Temperature Coefficient). It it undergoes a phase change when heated and limits the inrush current until it warms up. Unfortunately, when the amp is turned off, it often cools down at a slower rate than the plate current input caps discharge. As a result, if the amp is turned on shortly after it is turned off (a few seconds to a minute perhaps), there is much less inrush surge limiting and fuses often "go to be with Jesus". The degradation of the theta-J temperature coefficient of an NTC to ambient can be caused thru use (all mechanical things fail). It can also be caused by the accumulation of "fur" shed from "dust bunnies" afoot. If the inside of the amp power supply section looks "fuzzy", it likely ain't mo(u)ld. ;D ;D Also, if its warm there (you know, like in the summer), they don't cool down as fast. Now, if BOTH the heaters AND the capacitor input power supply are switched on at the same time (you know, that which happens when one (in)advertently uses the power cord as the on/off switch  ), the lord of the fuses is prone to visit more often. Don't do this. It apparently is leaving a mark.......(or at least an impression). Fortunately, your amp IS working properly. Leo didn't provide two power supply switches because he was kind and had extra switches to get rid of; he was cheap and had to use two. Don't change the fuse size. Don't abuse the amp, pay attention.  Luke, trust the fuse, Luke. Oh, and I almost hate to mention this, but the Twin Reverb schematic that you posted .......... www.fender.com/support/amp_schematics/pdfs/65_Deluxe_Reverb_Schematic.pdfWell, now you have too experts that have chimed in (it is a Deluxe Reverb after all). |
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Post by mr_sooty on Apr 29, 2009 0:12:11 GMT -5
Oops. Except that these two experts appear to disagree. Who to trust? Now I don't understand most of your post, but I appreciate you backing your opinions up with techno jargon, makes me feel you know what you're talking about. So you're saying that it's reasonable to expect these fuses to go when not following the right sequence, and that my best solution is to keep a few spare handy, and be more diligent when I switch it on? I'm happy with that, if it means I don't need a trip to the amp tech. And you're saying stick with the fast blow? Do you think there's anything wrong with using a slow blow? |
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Post by mr_sooty on Apr 29, 2009 0:56:11 GMT -5
Actually, this is interesting, because I probably have done this quite a bit. I'm often tinkering with something, or comparing amps or whatever, so it's possible that when the fuses have blown that I have turned the amp off and on again within a short space of time. Also, all the fuses have blown at home, which is where I tend to do this kind of tinkering. I thought maybe it was something to do with the wall socket, but it's probably more to do with switching it on and off too often and in the wrong sequence. It seems I may just need to be more careful with this one. My PV Classic 50 seems to handle the abuse better.
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Post by sumgai on Apr 29, 2009 1:48:21 GMT -5
sooty, Your PV Classic is designed more like the original circuits found in Fender, what Chris called the inductor-fed power supply circuits. That's why it doesn't react so badly to being powered up/down in sub-optimal switch configurations, unlike your new amp, which is more sensitive to switch order due to the power circuits being capacitor-fed. What Chris said is absolutely spot-on (regardless of how much/little sleep I got that day), however, it's moot - using the slow-blow fuse negates the need for maintaining a proper switching sequence, regardless of the power-supply circuitry and/or the switch arrangement at the time of power up. You'll have to await clarification from Chris as to why he didn't state clearly "Yea" or "Nay" on slow-blow fuses, sorry. You could experiment with a slow-blow, and see how things work out. The same rating, 1 amp, will be just right for your FDRRi. It'd be up to you to determine how you like the results. HTH sumgai |
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Post by mr_sooty on Apr 29, 2009 3:03:36 GMT -5
You could experiment with a slow-blow, and see how things work out. It'd be up to you to determine how you like the results. I'll like the results just fine if it blows less fuses, not so much if I somehow do some sort of damage to the amp by using the wrong fuse. But it seems it couldn't really do any harm. I really appreciate the advice. |
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Post by ChrisK on Apr 29, 2009 12:00:29 GMT -5
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Post by mr_sooty on Apr 29, 2009 16:44:24 GMT -5
OK, cool. So your advice is don't panic, nothing major wrong that I should be concerned about, stick with the fast-blows, be more diligent with my start up.
Confirm?
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Post by ChrisK on Apr 29, 2009 16:57:12 GMT -5
The fast-blow 1 Amp fuse has an I2 A2 Sec. rating of 0.69
The slow-blow 1 Amp fuse has an I2 A2 Sec. rating of 14
At a 2 amp (over)load, the fast-blow fuse will open in 0.4 seconds.
At a 2 amp (over)load, the slow-blow fuse will open in 20 seconds.
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Post by mr_sooty on Apr 29, 2009 18:54:45 GMT -5
The fast-blow 1 Amp fuse has an I 2 A 2 Sec. rating of 0.69 The slow-blow 1 Amp fuse has an I 2 A 2 Sec. rating of 14 At a 2 amp (over)load, the fast-blow fuse will open in 0.4 seconds. At a 2 amp (over)load, the slow-blow fuse will open in 20 seconds. So I probably don't want to expose the electronics to an overload for 20 seconds then do I. It's hard to get straight forward yes's and no's from you! Lol. I have to interpret. I think that was a confirmation that what i said in my last post was correct. It'd be awesome if you could check what I said in the post I did before this one and just confirm that what I've assertained from what you've said is right. |
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Post by ChrisK on Apr 29, 2009 19:14:41 GMT -5
I wouldn't. You are correct sir. I'm not going to give a simple yes or no here since it isn't simple, and I don't know all of the design basis' that Fender used for specifying a 1 amp fast-blow fuse. If you use a different fuse than specified, you've violated the warranty. Now, one could put the correct fuse back in (if remembered) before obtaining warranty service..... Yeah, we call that thinking/understanding. ;D Hmmm...... ;D ;D I did. What you've ascertained from my post before this one, and the one two posts before this one, as well as the post three posts before this one is what I said. I investigated the public share listings of a few major fuse manufacturers and have not found any evidence that Fender et. al. owns any major stock in them. As a result, I tend to believe that Fender have specified the 1 amp fuse for proper engineering design reasons. One might check Harmony Central for fusing reviews. But then, few folk plug these in upside down. |
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Post by mr_sooty on Apr 29, 2009 19:52:51 GMT -5
Cool, thanks Chris. I actually appreciate that your posts give me some kind of understanding about what's going on. I don't mind having to think a bit. I've learned a lot from you over the last few years! I still have no idea what you're talking about half the time though. One day I'll get around to reading the Electronics reference book my wife gave me for Christmas!
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Post by ChrisK on Apr 29, 2009 20:11:21 GMT -5
Nah, then she'll expect you to fix that broken toaster, oh wait, hmm, a power attenuator! After all, a toaster is just a power resistor. I don't know how hard and fast you'll have to play to get it to pop up though. 220, 221, whatever.  |
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Post by sumgai on Apr 30, 2009 2:02:31 GMT -5
Chris, I'm surprised.  I checked those spec sheets, and found that the curves tell the true story, not just a number in a column. (For those tired of my tirades, you can jump to the summary below - it's in red.) mr_sooty, Essentially, if you use a fast-blow fuse, and the current draw raises to 2 amps, the fuse will blow in about 0.3 seconds. But a slow-blow fuse, passing the same current, will blow in something like 11 seconds. Yes, that sounds bad, but as Chris has hammered several times, tube circuits, when operating at high-power levels, can easily draw up to twice their expected ratings. That doesn't usually occur for more than a second or two, but most tube circuit components can handle this kind of abuse..... although I must note, this is the primary cause of parts wearing out, they are aged much more quickly by this exceeding of their ratings. Now, realistically speaking, how often does a tube amp draw twice its rated power? Not very. Another way to look at it is, how often do you play it on the dime (maxed out)? Probably not very, eh? Unless you constantly crank it to Spinal Tap levels ("But these go to eleven!") then your amp really is no danger of suffering this kind of power draw. So, just when can it draw enough juice to cause problems, like blowing the fuse? Fair question. For the most part, a component can break down slowly, but when it reaches what we'd call the danger point, it will fail catastrophically. In the worst case scenario, that'd be a direct short of the B+ (the high voltage to the tubes) straight to ground. In such a case, the current draw becomes nearly infinite, which blows the fuse, no matter what its rating, and its blow speed, fast or slow. Yes, there will be lots of middle-ground cases, but for the most part, if they are gonna draw enough current to damage themselves, it's probably enough current to blow the fuse. As if that weren't enough, real world experience bears this out. In point of fact, Fender (which Chris rightly points out is just as susceptible to liability for their engineering practices) has as been using a slow-blow fuse in all of their tube amps, at least those for North American consumption, since Day One (in 1946 or thereaboots). To assume that they've now changed their minds would properly lead one to also assume that they made a mistake in the past, and are now doing things correctly. To that I say, well - there goes 60 or more years of experience, down the tubers. Gee Wally, we must've been real lucky, huh. Nope, didn't happen that way. As another example of what's acceptable engineering practice in the real world, bear in mind that literally every copy-cat amplifier in the world that was built after the first Champion 600, they all used the same fuses as Fender's circuits.... yep, you got it - slow blow jobbies. And remember, this was in other countries, where they may think a little differently (and make a lot of funny laws according to that thinking), but they still followed pretty much accepted practices - a slow blow fuse of low rating in a tube amplifier is a good thing. Using a higher rated fast-blow fuse would invite trouble, if for no other reason than a failing (but not yet fully failed) component might not trip that higher rated fuse, but a properly rated fuse (proper in this case, meaning for the mean current draw, not the maximum) would most certainly turn the consuming public against tube equipment, because they couldn't be turned on but the fuse would blow nearly every time.  One more thing to consider - Fender no longer does its engineering in-house, it's nearly all hired out. This means that many designs are brought about by so-called engineers who weren't around in the old days, and are relying on second-hand knowledge (providing they didn't sleep through class that day when the prof covered tubes). Even a re-issue design is copied, then "vetted" to make sure that the requisite components are still available, and that the design will pass muster with all of the various nation's "consumer safety and protection agencies" (think UL and their brethren here). That means, if no one understands, intimately, why a slow blow fuse is required on a piece of tube gear, and if all they do is consult a table that tells them only half the story, then they're gonna play it safe, and go with the component rated to guarantee acceptance by said rating agencies. If you haven't already done so, read Chris's link to Harmony-Central, and juxtapose what I've said against the comments on blown fuses. Whew, I've been on a right tear, haven't I? Well, here's where the rubber hits the road.... I'll go so far as to stick my neck out on the chopping block. If your amp is damaged by the fact that a slow-blow fuse refused to act in time to prevent damage to the innards, then I'll personally fix it for free, and pay for the shipping. (Errr, one way, back to you. After all, NZ is not just down the street from me. ) Summary:Most amplifiers, particularly venerable ones like the FDR, aren't gonna draw just twice the power when a component goes bad. The components used therein, and their placement within the circuitry, pretty much says, 'if it's bad, then a major current draw will come into existance, and that's gonna blow the fuse, fast or slow, period. </summary> HTH sumgai |
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Post by mr_sooty on Apr 30, 2009 5:50:11 GMT -5
The problem is that you guys both clearly know what you're talking about, yeat offer conflicting advice. Both your arguments make sense.
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Post by newey on Apr 30, 2009 6:01:19 GMT -5
Mr S-
Yes, they both make sense, but there was a key word in ChrisK's post- "warranty"- that SG doesn't mention.
I would do this---buy several fast-blow types, and practice religiously following the start-up sequence. If you still find yourself blowing fuses, try thr slow-blow ones.
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Post by sumgai on Apr 30, 2009 10:40:18 GMT -5
newey, I did mention the "w" word, warranty. However, I don't have the corporate moxie to stand behind any and all products with my name in them, all over the entire planet. Even so, I do have the personal moxie to stand behind my claims on a personal level. Yeah, I get to pick and choose, but then again, I'm not in the public eye for off-shoring all my resources, so I'm not exactly a bad guy, eh? And this isn't the first time for me either, you'll recall at least one instance on this board that I've made that offer, in the past. More often, if you include the casual statement that I'd buy something for our non-North American members and ship it to them, to help them out on shipping costs. So far, only one person has taken me up on that one, and I think he's happy. But in the end, it's mr_sooty's comfort level that needs to be stroked, not Chris's or my ego. I heartily agree that your trial method has merit. Figure it this way - if one can sit down and learn to play a song by rote, then one should be able to do the same thing with a simple thing like a power-up/power-down switching sequence, right? ;D mr_sooty, I'd do it this way - prepare to buy a large stock of fuses, but only buy one pack at a time (usually 5 to a container (at least here in the USA)). Write a note and tape it to the top of your amp, with low-tack tape. Now, if you still haven't gotten the hang of it after a month, consider moving to slow-blow fuses, and settling back with a can of Fosters, and heave a sigh of relief. Unlike most engineers, I'm prone to say "done never is".  (Hmmmm, that's like sumgai's corollary to "If it ain't broke, fix it 'til it is".) HTH sumgai |
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Post by ChrisK on Apr 30, 2009 12:13:41 GMT -5
Actually, this is backwards. There's a saying in the product development world; There comes a time in the life of every new design when you need to shoot the engineer and put it into production....Perfect never is. True product development engineering is the art of good enough. Switch sequence training isn't likely going to help; I might presume that the power cord isn't actually being used as the switch, a power strip is. You likely might be just fine with a slow-blow fuse. After all, The DR's over the years may have had them. However, this isn't a DR, it's a '65 DR reissue (FWIW). While CBS may have killed the classic Fender tube amp line after they took over (the amps became boringly consistent rather than both exceptional and crappy), they did bring the practice of design engineering to a product line that was taken, for the most part, out of tube application manuals. We always remember the exceptions, both the really good and the really bad. I remember some great gear from the '60s and, well, the '60s. I remember a lot of crappy instances too. |
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Post by cynical1 on Apr 30, 2009 13:53:12 GMT -5
True product development engineering is the art of good enough. Amen. |
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Post by mr_sooty on Apr 30, 2009 17:51:15 GMT -5
I have a stock of fast blow fuses already, so I'll use them all up for now. Hopefully if I'm more diligent (which I am being) it'll take me a while to use them all up. If it doesn't. I'll try a slow blow. The warrantees already well and truly voided anyway.
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Post by sumgai on May 1, 2009 1:21:32 GMT -5
sooty, Good plan! BTW..... Holy Smokes, is that a LEGO guitar man?  sumgai |
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Post by mr_sooty on May 1, 2009 17:23:34 GMT -5
No, that is Soundwave, a Transformer. This version is from the current 'Transformers Animated' series. Traditionally soundwave turned into a walkman, and he had tapes that turned into animals. One such tape was Laserbeak. In Transformers Animated, Soundwave is a van, and Laserbeak turns into a guitar that kind of sits on his roof rack. In the TV series, he also has 'Ratbat', who turns into a key-tar! All class!
I used to be a mad nut Transformers collector, but I sold most of my collection to upgrade my guitar rig. That particular Soundwave belongs to my son, who is the new mad nut Transformers collector in our family.
Incidentally Sumgai, I noticed where you said you offered to help out people outside of North America by being a shipping drop off point. I will definitely keep that in mind!
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Post by ChrisK on May 2, 2009 21:14:48 GMT -5
I was looking thru my copy of "The Tube Amp Book" by Aspen Pittman and noticed that on most of the Fender tube amp schematics therein, there was a 2 amp fuse. Most amps with a standby switch had the B+ filter caps on the transformer/rectfier side rather than the plate side. A couple had them on the plate side. This means that the capacitor inrush current still occurred when the filaments were warming up.
All but one or two of these amps did not have an NTC thermistor in the AC power input circuit. Most fuses were not specified as slow-blow.
It seems that the reissue amps use the NTC's. There must be reasons for this. After all, only the transformers are different (newer magnetics and wire insulation ratings), the capacitors are different (better, lower ESR), and the tubes are different from those made in the '60s and '70s.
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Post by sumgai on May 3, 2009 13:42:17 GMT -5
Chris, As you noted earlier in this thread, it's the inrushing filament current that causes the biggest power surge, not the plate current. No matter which Class of operation the amp actually works at, the plates never draw nearly as much current as the filaments. The proof of that is Q.E.D. - simple voltage drop measurements through a series resistance, and a one-step application of Ohm's Law lays it out in black and white. As a 'double- check', it's no longer as simple to observe, due to supply and demand over the ages, but it used to be that if one wished to have separate transformers for the various voltages (grid bias, plate, and filament), one could do so. At that point, it was extremely obvious that the filament transformer was much larger than the other two. Why? Because it had to deal with a lot of power, comparatively speaking. Speaking of temperature coeffecients..... (A short primer for the non-engineers amongst us.) A tube's filament generally has a higher resistance as it gets warmer, exactly like a standard light bulb. Thus as power is first applied, the current draw is immense, almost to the point of a short circuit. A fast blow fuse just might interpret this as a short, and blow. A slow blow fuse sees this the same way, but has a time lag before blowing. Thankfully, because the filament resistance raises with the heat (sort of self-governing, ain't it wunnerful?), the current draw decreases, and the fuse never reaches the point of blowing. As it happens, I've got nearly all of Pittman's books, as well as a boatload of schematics I've saved over the years from many sources, only a few of them the actual factories. I now note that nearly all of Fender's drawings specify a slow blow fuse, buy many other manufacturers do not. In the majority of cases, they simply use a larger value fuse, ostensibly to compensate for that inrushing current to not cause the user so much headache. FWIW, I'm on the side of safety first, with probability and user convenience running neck-and-neck for second. I'd say "if it was good enough for Leo for umpty-squat years, then it's probably good enough for the rest of us, for as long as we use tubes." Nothing significant has changed over the past 6 decades that necessitates a "re-think" of basic, sound engineering practices when it comes to tube circuitry. Essentially, I'm saying that it's been proven safe over many decades, and that the probability of a slow blow causing more problems than it solves is incredibly small. Again, personal, experience, anecdotal evidence, and generally accepted practices are my guiding lights here. One more item for consideration. I'm reminded of an amp that came into the shop about 5, maybe 5½ years ago, a Rivera that was used as a house amp at a local bistro. The bar manager said that it was making funny noises, so I turned it on for a quick test. Lo and behold, both output tubes were glowing cherry red, and I mean bright! But the fuse wasn't blowing. That's a frightful condition, to say the least. I had to ask myself, how is that these things are lighting up the inside of the cabinet, yet the fuse isn't blowing? I even stuck a new fuse in, just to be sure. Turns out it was borderline, the current draw was nearly twice what I expected, but it was all coming from the grid voltage underbiasing the tubes. A pair of bias resistors had been used that were underated, power-wise. They couldn't take the heat, and blew up, thus letting the tubes get way too hot. Not hot enough to blow the fuse, but the potential for environmental damage was exceedingly high! (A lot of smoke and more than a puff or two of nasty gasses.) Moral of the story: The fuse is not your be-all, end-all protector! Use your eyes (and ears and nose...), always check out your rig before you go live! HTH sumgai |
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Post by ChrisK on May 3, 2009 21:09:23 GMT -5
Well, this IS what separates light bulbs from flash bulbs. I'd try to err on the side of safety and equipment preservation also. I'd rather have a $1 fuse blow rather than a $50 tube blow. If fuse failure is a problem in performance, replace them with slow-blow if not supplied this way from the factory. Just remember to put the correct ones back in so that one may experience their blowing during practice to detect pending failure. In certain ultra-secure areas where the delivery of certain high-yield weapons is directed and expected; all computer and control equipment have their fuses and breakers overridden when they go on-line as the primary unit.  |
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), the lord of the fuses is prone to visit more often.
I checked those spec sheets, and found that the curves tell the true story, not just a number in a column.
