Hi Guys
What approvals you need depends a bit on how much money you are willing to spend to have peace of mind and how much you believe that it will make a difference. To sell through stores usually requires CE approval etc. If you sell direct then any approval is fine.
Ethics of how this works and transpires depends a lot on who's radar you fall under. Mesa is run by an egotistical hypocrite who will block potential threats to his profits however he can. If he suspects you are using something he would like to think he invented, say electricity, he will threaten you in ever so kind a manner. Most are intimidated and go out of business or find some quieter way to sell their wares.
If you choose agency approval, it is best if you can get a "family approval" for the product line. This just means that all the products are built the same way and possibly use the same power supply. UL should offer the same packages as CSA inasmuch as you can get just Canada or US coverage, North American coverage, NA plus Europe, etc. Obviously Istek or ETL offer better pricing.
Your fear about which label will be accepted where is mostly the result of what those agencies wish for you to believe. There is a bit of fear mongering indulged in by the agencies and the insurance companies.
Have fun
Kevin O'Connor
What approvals you need depends a bit on how much money you are willing to spend to have peace of mind and how much you believe that it will make a difference. To sell through stores usually requires CE approval etc. If you sell direct then any approval is fine.
Ethics of how this works and transpires depends a lot on who's radar you fall under. Mesa is run by an egotistical hypocrite who will block potential threats to his profits however he can. If he suspects you are using something he would like to think he invented, say electricity, he will threaten you in ever so kind a manner. Most are intimidated and go out of business or find some quieter way to sell their wares.
If you choose agency approval, it is best if you can get a "family approval" for the product line. This just means that all the products are built the same way and possibly use the same power supply. UL should offer the same packages as CSA inasmuch as you can get just Canada or US coverage, North American coverage, NA plus Europe, etc. Obviously Istek or ETL offer better pricing.
Your fear about which label will be accepted where is mostly the result of what those agencies wish for you to believe. There is a bit of fear mongering indulged in by the agencies and the insurance companies.
Have fun
Kevin O'Connor
I just picked up a Peavey Classic 50. And like many amps, it has a heavy steel chassis but no bottom; it's open to the wood on the bottom. I also wanted to be able to run it outside the case, and it needs a bottom for the fan air flow to work correctly. So I had the local metal shop shear a sheet of 1/8" aluminum and tapped the chassis, so that the wiring is completely enclosed in metal. It's better-shielded now. Any insulation failure can short to the chassis and blow a fuse or breaker. Any overheated power resistor that unsolders itself and drips solder won't be smoldering on wood for hours.
I'm really not that keen on fan cooling INSIDE the chassis, though it can be a good idea over the tubes and transformers ABOVE the chassis. Perhaps the air intakes should be filtered. I just don't like the greasy dust that accumulates.
Guitar amps are built to a market price point, and they take advantage of low expectations borne of questionable traditions. IMHO there's plenty of room for improvement.
IMHO try to make an amp fully enclosed in metal, if possible including ventilated metal around the tubes. Then put it into a large well-ventialted wooden case for protection and for traditional appearance if you wish.
I'm really not that keen on fan cooling INSIDE the chassis, though it can be a good idea over the tubes and transformers ABOVE the chassis. Perhaps the air intakes should be filtered. I just don't like the greasy dust that accumulates.
Guitar amps are built to a market price point, and they take advantage of low expectations borne of questionable traditions. IMHO there's plenty of room for improvement.
IMHO try to make an amp fully enclosed in metal, if possible including ventilated metal around the tubes. Then put it into a large well-ventialted wooden case for protection and for traditional appearance if you wish.
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CTR televisions were a major source of domestic fires until recent flat-screens. Anyone who's opened an old TV knows about the thick layers of greasy dust that covers the CRT, flyback, and high-voltage leads, and all those glowing heaters. All in a ventilated somewhat combustible wood or plastic case. Of course, a CRT TV is an extreme example because the static attracts dust, and sometimes they are left on continuously.
What can I say, I originally come from Chicago where every bit of house wiring must be enclosed in metal conduit or metal boxes. I expect better for high-voltage equipment we expect to get hot in normal use.
I've seen these same Peavey amps with burned traces when a tube fails. Enough dust and that fan might really get a fire going! I've seen enough badly-burned circuit boards to know unexpected things happen. I don't know if a metal cabinet would help when a transformer shorts...just hope the fuse blows.
Marshalls and Fenders aren't bursting into flames on a regular basis. But I would suggest that current practices define a minimum requirement, and better methods are not excessive.
What can I say, I originally come from Chicago where every bit of house wiring must be enclosed in metal conduit or metal boxes. I expect better for high-voltage equipment we expect to get hot in normal use.
I've seen these same Peavey amps with burned traces when a tube fails. Enough dust and that fan might really get a fire going! I've seen enough badly-burned circuit boards to know unexpected things happen. I don't know if a metal cabinet would help when a transformer shorts...just hope the fuse blows.
Marshalls and Fenders aren't bursting into flames on a regular basis. But I would suggest that current practices define a minimum requirement, and better methods are not excessive.
There's VERY little that's true in those sentences
Dust has pretty well zero effect inside a TV, and 'all those glowing heaters' is only one in the CRT (or three in the CRT if you like?).
TV's have also never been a major source of household fires, such fires are exceedingly rare, and most such are caused by bodged repair attempts.
They also aren't very combustible, with most of their construction being 'self extinguishing'.
In 40+ years as a professional service engineer I've NEVER found dust to be any problem at all - nor spoken to an engineer who has.
If you do want to remove the dust, a vacuum cleaner and a soft brush is all that's needed - just hold the vacuum cleaner nozzle above the circuit and brush gently. Be VERY careful, while the dust doesn't cause any problems, inept removal of it often does.
They don't 'burst in to flames' because your entire premise is incorrect, and it's unlikely that metal casings would make them any safer.
Incidentally, there have been occasional metal cased valve amps over the years, but for guitar use you want something rather better capable of taking abuse.
There's VERY little that's true in those sentences
Dust has pretty well zero effect inside a TV, and 'all those glowing heaters' is only one in the CRT (or three in the CRT if you like?).
TV's have also never been a major source of household fires, such fires are exceedingly rare, and most such are caused by bodged repair attempts.
They also aren't very combustible, with most of their construction being 'self extinguishing'.
In 40+ years as a professional service engineer I've NEVER found dust to be any problem at all - nor spoken to an engineer who has.
If you do want to remove the dust, a vacuum cleaner and a soft brush is all that's needed - just hold the vacuum cleaner nozzle above the circuit and brush gently. Be VERY careful, while the dust doesn't cause any problems, inept removal of it often does.
They don't 'burst in to flames' because your entire premise is incorrect, and it's unlikely that metal casings would make them any safer.
Incidentally, there have been occasional metal cased valve amps over the years, but for guitar use you want something rather better capable of taking abuse.
Nigel, thank you for your experience and opinion. I don't really know, I just know what I prefer; an admittedly poor criteria. Is there more truth in your sentences? Two different opinions. Minmum standard or perhaps better...it's not a major issue, obviously not much of a real problem or it would have been addressed, like I said guitar amps are not shooting flames out on a regular basis, or humming bad when you reach for the cabinet, yet it seems clear to me which I prefer. You have more experience than I do, perhaps better judgment or perhaps more indoctrination that the status-quo is sufficient. Hi-fi and PA has had a different standard, maybe it's just the different background we come from.
I said an "old" TV, which often has MANY tubes and usually plenty of greasy sooty dust inside. I've seen plenty of problems with carbon traces on flybacks that seemed to start with accumulated dirt that turned corona into a flashover causing carbonized deposits eventually making a permanent trace slowly burning its way into bakelite or potting compound. I don't know the real history, just seen what looks like evidence, maybe there had to be a breach in the insulation first? Dirt will certainly originate such high-voltage problems in an automotive ignition, but that's really high voltage. Unfilterd fans and dirt are really a seperate subject, guitar chassis are not usually open, just open to wood-ish materials. The way the Peavey Classic 50 sucks air thru the lower chassis is not the standard. You're right that TVs are indeed the least frequent 'key cause' appliances that most countries track for starting domestic fires, admittedly low compared to any heating devices, yet that small percentage of a common device makes a reasonably large number of incidents (and recalls). Yes, there's some urban myth invovled, and TVs are often blamed for fires they didn't start because they show so much damage and cause so much toxic smoke. How flammable the cabinets really are depends a lot on the country's voluntary standards, and chemical companies that make retardant coatings have inflamed the issue (bad pun intended). Until recently, England didn't have stringent voluntary standards, and the stats showed some correlation. In the US plastic and wood cabinets have been chemically treated to self-extinguish for many years, guitar amp cabinets are usually not. Untreated, wood and plastic TV cabinets are far from self-extinguishing because they are designed to ventilate well with chimney convection; the components may or may not start the fire, and don't burn much but untreated cabinets sure do in countries that permit them. Accurate tracking of original causes is difficult, and investigators rarely trained in electronic details. Yet TV chassis are more likely to have components and circuit boards enclosed on all sides including the bottom than guitar amps, and the RF sections almost always fully enclosed (admittedly for somewhat different yet somewhat related shielding reasons). This Peavey was full of a lot of sticky, greasy dust stuck to the internal wires when I got it, mostly because of unfiltered fans, and it sure looked like it didn't flow cooling air correctly anymore and the debris would likely burn pretty good, probably in one flash (would it leave carbon traces?). Amazing the fan turned (noisy, had to replace it). Of course after a TV causes a house fire nobody brings the melted TV in to you for repair; if you're not a fire inspector I wouldn't expect a repairman to be ane more knowledgeable about frequency of appliance fires. But tell me you haven't seen burned traces, burned resistors, charred boards, hot resistors unsoldering themselves and dripping hot solder onto wood, smoking transformers, cracked parts that spark, carbon traces that conduct etc. Untreated vinyl-covered wood smolders or burns a lot better than metal. And wood doesn't cause an insulation failure from abrasion and/or heat etc. to short to ground and blow a fuse or breaker, which is why also I favor unpainted metal chassis (other opinions abound). Televisions are still a "key cause" of domestic appliance fires tracked in most developed countries. And common guitar amplifier construction with an open chassis against untreated wood would not be allowed for TVs in many countries, and would not meet the current voluntary standards in the US for TVs. IMHO mediocre guitar amp chassis design is tolerated because of the mediocrity of traditional guitar amps in this regard. And many of the latest low-noise single-ended class A guitar amps designed for recording do have a bottom on the chassis, and some claim it to be a feature.
It's just my opinion that it's best to have high voltage enclosed in metal (or glass I guess) on all sides, not leaving one big side exposed to wood or MDF. I've seen amps that had tin foil on the wood cabinet surface, getting all scraped up, which is probably worse. I'm not in favor of metal cabinets instead of wood, I'm saying in my opinion it's best to have a metal case, then slide it into wood if you need it protected and road-worthy (then it should have an ATA case in addition). There's real reasons to use a metal chassis, not cardboard or wood; that's obvious, and like I said a minimum standard. If the minimum standard is good enough for you, go with the majority of current designers who also consdier it a reasonable hidden cost compromise that's not visible to the consumer and not exposed to abuse or the user and not really dangerous. Many obviously agree with you. But I haven't heard one single supportable really good reason NOT to add a metal panel to close most current guitar amp chassis before installation into the wooden case except cost and weight, or ease of tight fit against the cabinet. Like I said, it won't help much for the dramatic smoky failures like a transformer short. But is there any real solid reason NOT to enclose a chassis on all 6 sides instead of only 3 or 5? I'm really curious what the shielding benefits are or aren't, and what's the best metal to use, whether it matters that the closures conduct etc. Is it best to wrap the whole box in mu-metal before the vinyl is applied (just kidding, imagine the cost) or copper screen? It just seems to me like "best practices" as opposed to mediocre "common practice". I'd like to hear new ideas, and genuine data. I see plenty of DIY amps in all-wood or all-plexigalss cases, and some claim genuine benefits I find difficult to swallow. I'm open to any real reasons favoring the chassis exposed to wood, but haven't heard any good ones yet. Maybe the best arguement is not cost or weight but simple accessibility, fewer screws to remove, less to install? The majority of well-made tube hi-fi amps had an encloded chassis (with exposed or caged tubes), I assume an attempt at better shielding, even models that then went into pretty wooden cases. IMHO hi-fi just a higher performance standard than guitar amps. Or maybe I'm wrong and they just wanted the wooden enclosure to be an optional additional-cost feature, or to be mountable in Barzilay console furniture or built-in. I'd really be interested in any real data comparing the shielding of an open chassis versus closed. I've never understood designers who make a nice shielded chassis then stick half the power transformer thru a hole, instead of mounting it elevated a few more inches even farther away from any high-gain sections. My understanding of shielding is incomplete. Perhaps it's less critical with good layout, shielded internal wiring, etc. Maybe it's inconsequential compared to the noise the guitar picks up. I'm amazed at the ribbon cables in this Peavey, even computer ribbon cables usually run a ground wire between data wires. I'm not claiming to have all the answers, but I'd sure like to hear some. Please excuse the length of this diatribe.
Perhaps you need to define 'old'? - but I doubt hardly any TV's of that age are still in use, or have been for many decades.
Going back to the 50's and 60's (as you appear to be doing?) the safety standards were FAR, FAR lower than they have been in recent decades.
Back then often EHT stages were open, with paxolin shrouds around some EHT transformers - but anything remotely 'modern' will have pretty well sealed and potted EHT stages.
While valve guitar amps might be ancient technology this doesn't mean they aren't built to modern safety standards and anything you build at home should comply with such standards (as far as possible - but mostly it's just common sense).
sometimes tube amps (MusicMan in this case) really DO catch fire from within: Johnny Winter Vienna 14 nov 2009 burning amp - YouTube
Hi Guys
It does not require tubes for an amp to be a fire hazard. Marshall's 3210 heads burned up frequently due to a poorly designed reverb driver circuit that could oscillate with little provocation. I saw a few PCBs with holes burned right through them. All for the sake of savng one resistor...
Have fun
Kevin O'Connor
londonpower.com
It does not require tubes for an amp to be a fire hazard. Marshall's 3210 heads burned up frequently due to a poorly designed reverb driver circuit that could oscillate with little provocation. I saw a few PCBs with holes burned right through them. All for the sake of savng one resistor...
Have fun
Kevin O'Connor
londonpower.com
I was a TV repair tech in Miami from 1968 to 1971. Many houses did not have air conditioning and the humidity ranges from 50 to 100%. The 25 KV second anode HT in a color set does attract dust which collects moisture and turns to a brownish slime in the presence of ozone. At 25 KV it is conductive! GE was the first manufacturer to make the high voltage cage from a plastic material. HV + brown slime + plastic + heat and humidity = FIRE! I saw several cases. I never saw a cabinet combust though. Usually there was a burnt and melted high voltage box and severe soot damage inside the cabinet. Some of these TV's were completely replaced by GE.
From 1971 to 1973 I was the service tech at an Olson Electronics store next to the University of Miami. I was at an outdoor rock concert and witnessed one of the many Ampeg SVT flame fests that occurred in the early version amps. The band was running the amp full blast into a pair Traynor of 8 X 10" cabinets that were likely not rated for 300 watts. I heard the sound of voice coils melting and becoming unwound (rattling distortion) followed by loss of speakers. It took less than a minute before all the remaining speakers were blown followed by flames and intense smoke shooting from the amp. In a rare twist the amp wound up in my service department for repair because the local big name music shop (ACE Music) would not fix it. OPT, Power transformer, 1 or 2 6550's and several resistors were fried. The wood cabinet was not involved and just needed a little cleaning.
The flames seem to be centered around one of the speakers. I have seen (and caused) speakers to catch fire. It usually involved plugging them into a wall outlet though! There are plenty of examples on Youtube.
I to have done that
Not for a number of decades though - it's the sort of thing you do when you're young and foolish.
Better here of course, with 240V mains
IN4148 diodes go BANG really nicely directly across the mains as well.
Young, yeah I was about 19. Olson HQ had a bad habit of finding nothing wrong with some of the speakers we returned under warantee. I made sure everything we sent back was indeed quite defective.
Most Olson branded raw drivers were made by Utah or Eminence. We had a 12 inch coaxial that sold for about $15 in 1972. It was a decent sounding speaker but wasn't up to UM frat party power handling. Upon "testing" prior to return the woofer would emit one loud pop, but the tweeter would faithfully reproduce all the HF noise on the power lines until the crossover cap exploded, often several minutes.
I have been building tube amps with wood cases for over 40 years, no problems. The only material that I have had problems with is Plexiglass. It melts when near hot tubes. Lexan and most Polycarbonate materials are OK.
I have seen some wood cabinet based guitar amps that were just plain dangerous. Granted they were old, but I have seen designs where it was posible to reach in the back and touch live parts.....no power transformer either.
I have a Park (Marshall) 100 watt amp with only one small vent across the top to let the heat out. No place for cool air to enter to displace the hot air. The wood cabinet gets hot on top, but the amp still works after nearly 40 years and still has all the original parts, except tubes.
Build it right and there will be no problem. It should be impossible to touch hot (electrical or temperature) parts. All exposed metal must be grounded. There should be ample ventillation and the IR energy radiated by the output tubes should be allowed to escape the box wherever possible.
I have seen some wood cabinet based guitar amps that were just plain dangerous. Granted they were old, but I have seen designs where it was posible to reach in the back and touch live parts.....no power transformer either.
I have a Park (Marshall) 100 watt amp with only one small vent across the top to let the heat out. No place for cool air to enter to displace the hot air. The wood cabinet gets hot on top, but the amp still works after nearly 40 years and still has all the original parts, except tubes.
Build it right and there will be no problem. It should be impossible to touch hot (electrical or temperature) parts. All exposed metal must be grounded. There should be ample ventillation and the IR energy radiated by the output tubes should be allowed to escape the box wherever possible.
Really? It didn't shorten the life of any caps in that valuable vintage Park?
I just picked up a nice old running Super Twin chassis: 180 watts with 6 6L6s etc. and healthy-sized transformers that run pretty warm. The way Fender hangs the chassis upside-down it can get REALLY hot. This is the biggest upside-down amp I know of except perhaps the reverb version. This has no reverb or tremolo or effects loop or balanced direct out, one channel, really nice tone controls, then a 5-band rotary graphic EQ (with 5 inductors) but little usable guitar distortion. People are discovering they are better bass guitar heads than combo amps! But in the original big deep open-back combo case they got lots of ventilation. When people cram them into a standard Fender head case I can't imagine they get enough cooling air. I really don't want a fan. So I'm planning a taller cabinet, I imagine about like a Fender Super Showman with Reverb (which I don't have the exact dimensions for). And it will be a little deeper, like the combo, so the air flow out the upper vent in the cabinet's back plate will get around the chassis a bit better, and I'll make that upper cutout in the back plate slighty oversize for better airflow and for easier access to the speaker jacks etc. which the deeper cabinet will cause to be deeper recessed, and I'll relocate the lower two oval air intakes in the back plate a bit lower and enlarge them slightly, and I'll add some intake vents to the bottom of the cabinet, slightly taller feet to permit airflow from beneath, and the front of the cabinet will have two rectangular cutouts behind the grille cloth so that some air might actually come thru the grille. I'd replace that grille cloth with an open-mesh metal grate if it didn't look so industrial. I might even add some vents and grates to the sides of the cabinet. I think just making the cabinet a little taller will improve the chimney effect and improve air circulation in & out. Any other good ideas, short of a 'vertical' cabinet? Can I ventilate the INSIDE of the chassis via some vox or marshall style vents in the top of the cabinet, or will it accumulate too much dust or smoke & grease inside, or make the pots get dirt sooner?
I just picked up a nice old running Super Twin chassis: 180 watts with 6 6L6s etc. and healthy-sized transformers that run pretty warm. The way Fender hangs the chassis upside-down it can get REALLY hot. This is the biggest upside-down amp I know of except perhaps the reverb version. This has no reverb or tremolo or effects loop or balanced direct out, one channel, really nice tone controls, then a 5-band rotary graphic EQ (with 5 inductors) but little usable guitar distortion. People are discovering they are better bass guitar heads than combo amps! But in the original big deep open-back combo case they got lots of ventilation. When people cram them into a standard Fender head case I can't imagine they get enough cooling air. I really don't want a fan. So I'm planning a taller cabinet, I imagine about like a Fender Super Showman with Reverb (which I don't have the exact dimensions for). And it will be a little deeper, like the combo, so the air flow out the upper vent in the cabinet's back plate will get around the chassis a bit better, and I'll make that upper cutout in the back plate slighty oversize for better airflow and for easier access to the speaker jacks etc. which the deeper cabinet will cause to be deeper recessed, and I'll relocate the lower two oval air intakes in the back plate a bit lower and enlarge them slightly, and I'll add some intake vents to the bottom of the cabinet, slightly taller feet to permit airflow from beneath, and the front of the cabinet will have two rectangular cutouts behind the grille cloth so that some air might actually come thru the grille. I'd replace that grille cloth with an open-mesh metal grate if it didn't look so industrial. I might even add some vents and grates to the sides of the cabinet. I think just making the cabinet a little taller will improve the chimney effect and improve air circulation in & out. Any other good ideas, short of a 'vertical' cabinet? Can I ventilate the INSIDE of the chassis via some vox or marshall style vents in the top of the cabinet, or will it accumulate too much dust or smoke & grease inside, or make the pots get dirt sooner?
I don't know how much use the amp really saw. The story that I got is that it was found in a storage area inside an Atlantic City casino that was being renovated. It was found sitting on top of a pair of Altec A7's and a pair of the matching bass bins (B?).
The entire contents of the casino wound up at a scrap/surplus dealer in rural Georgia. The stuff was sitting in a large warehouse with broken windows, resulting in a thick coating of pidgeon crap all over everything. That is where I first saw it. I bought some tubes from the guy who ran the surplus yard. He didn't want to sell the amp because he was going to fix it someday.
Ten years later a surplus dealer friend bought the entire estate after the owner passed on. He plugged in the amp and it blew a fuse, so ge gave it to me. It had an extremely gassy (bright purple) 6CA7. I plugged in 4 EH EL34's and let it rip. I have put about 2 hours on it, with at least 1 hour at full volume. No signs of leaky or bad caps, so I boxed it up. I will eventually sell it and it is probably worth more as an unmolested original.
I could get my user name revoked if I told you what I am using for a guitar amp right now.
It depends on where you want to use the amp. Ventillation will improve the life of the components, but may not be the best idea if the amp will be used for gigging, especially in smoke filled bars. A brown sticky slime results.
My big amps use a PC fan that was intended for 12 volts, but run on rectified heater which is about 8 volts with a Hammond power transformer. The fan intake is filtered with the foam filter that is found in the plastic drive bay covers on cheap PC cases. Air goes in under the deck, up through the chassis around the tubes, and out through the top (no filter).
The way it has been done for 50 years is this:
1) the electronics is build inside a metal chassis. The chassis is grounded. Then the amplifier as a unit is mounted into a wood cabinet.
2) The back of the cabinet is left open (or mostly open) so the tubes can cool.Remember that tubes cool by radiation. For that to work the tube needs to "see" a clear path into the rest of the room.
Some boxes have small vents, but remember again tubes cool by radiation. There is no other way to transport heat across a vacuum. The glass is almost transparent to the radiation to it just shines onto the inside of the wood box. The box has a large surface area and re-radiates the heat.
Don't think for a minute that a tube amp is cool led like a cheap tower PC where heat sinks heat the air and then a fan blows out the hot air. It is not like that. The tubes are MUCH hotter than a CPU heat sink so it is radiation, not convection that cools a tube amp. (I said "cheap pc" because the better ones will us air ducting or conduction.)
About wood and heat: Some early Chinese spacecraft where designed to drop parts back to Earth. They actually used solid oak heat shields. The wood would turn to charcoal and slowly burn but it only had to last a few minutes. millions of years of forest fire and Darwinism combines to make oak reasonably heat resistant.
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Tubes do indeed radiate most of their excess heat in the form of IR radiation. The glass is not perfectly transparent to IR so it will absorb some IR and get hot. Much of the IR will impinge on metal components inside the amp causing them to get hot. Some of the heat will be conducted out of the tube via the base.
The OPT in a tube amp dissipates a few watts at most due to resistive and magnetic losses, yet it gets hot. Black ones get hotter that silver ones. This is absorbed IR radiation and it will raise the internal box temperature considerably, especially in a poorly ventillated box.
All of the conducted and reasborbed heat in a tube amp can be cooled by air flow. Heat generated by transformers and resistors can too. It is not necessary to establish a full cooling system in a tube amp like found in a good PC, but a little air flow will make a big difference in chassis temp.
I have built a few tube amps in Lexan cabinets. A small fan can be the difference between a melted amp and a cool runner.
Note: Don't use Plexiglass! It melts even with a fan.
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