The reason for the big power from tiny tubes comes from minimizing the voltage drop across the tube at peak current. This is mostly driven by these two things:
Tube selection. The tube in question needs to have a cathode with plenty of reserve emission capability to support high peak currents. You can't get big power if there aren't enough electrons in the cloud.....not the Microsoft kind of cloud. I can squeeze much more power from a 50C5 (7.5 watt heater) than a 6AQ5 (2.835 watt heater). More voltage will be dropped across the tube for the same current flow with the smaller cathode. The 32ET5 is the anomaly since it comes from the late tube radio era and incorporates more efficient cathode coatings......about the same emission from its 3.2 watt heater as the 7.5 watt 50C5.
The 6AQ5 can crank out 30 watts per pair, but it requires 400 volts of B+ and the tubes were dissipating 14.5 watts each at that power output....they won't live long.
The 50C5 will make the same 30 watts on 340 volts, but burns around 9 watts per tube.....they will live much longer.
The 32ET5 will also make 30 watts per pair on 340 volts. Thye are not quite as efficient as the 50C5 burning 9.5 watts per tube, but there is 4.3 watts less heat coming from the cathode, so the overall tube temp should be lower.
Class AB2 operation. In order to get the tube voltage drop down in the few volt range you must drive G1 positive. Sometimes quite a bit positive. This was not easily done in 1935, but some of the 1935 era tubes responded to AB2 quite well. The 45 DHT is commonly used for 1 to 1.2 watt class A SE HiFi amps. Mine runs class A2 and makes about 2 watts, an improvement, but not a big one. Where AB2 really shines is in push pull. There the same pair of 45's will easily make 20 watts.
The lowish idle current is needed to support high plate voltages. In order to avoid melting the tube, you need to keep the idle dissipation down to a reasonable level. Sometimes this means following the manufacturers dissipation rating. Some tubes can often eat more that the rated plate dissipation, but testing is needed. Even in a guitar amp the tube spends most of it's time at or near idle......keep it cool there, then let the peaks warm them up a bit. The peaks are relatively short compared to the thermal lag of the tube.
Lithium Ion cells will degrade, usually permanently, if discharged below a certain voltage. This does not usually cause flaming battery syndrome, but it can.
Lithium Polymer cells can go into a self destructive state if allowed to discharge too deeply, or if they are overcharged. This can happen instantaneously when over or under charged. More usually a localized damaged area will be created which can go critical sometime later, usually when the cell is heated.
I tend to use my portable PC sporadically, and the slow discharge caused by the electronics in standby is what scares me, so I use a mechanical relay to disconnect the battery completely when not in use.
Lithium paranoia (and the fact that I'm using Ebay sourced Chinese cells) convinced me to remove the battery on a recent vacation trip. I also had other items to power, so I brought a UPS to run everything. Run time for this PC and the music synths is beyond 6 hours from the 1500 VA UPS. I knew that the PC would be left in the sun and in a hot car for extended periods of time, so I ditched the battery. This may not have been necessary, and did cause the PC to be blown over twice by the strong winds.
Our extended family rented a large 4 story house on the Ocean in the outer banks of North Carolina for a week. There were 12 people from the ages of 3 to 83 present. I took this "once in a lifetime" opportunity to take over 35000 pictures, most in rapid sequence for the purpose of making some time lapse video for YouTube. I brought along three DIY music synthesizers and the portable PC loaded with Ableton Live. I set it up on the 4th story deck overlooking the ocean each day, and left it running so I could capture some ideas in Live and on camera whenever the mood struck me. I also set it up in my room for playing at night. Unlike the other people in the house I never turned the TV on or played a video game.....you can do that stuff at home.
I'll post some videos on Youtube once I have had the time to organize the pictures and musical ideas into something that resembles a coherent video with a synthesizer sound track.......no guitars though I may add some here at home.
The UPS idea worked out so well that I may attempt to build something like it without the weight penalty of lead acid gel cells.......that thing was heavy. I carried it down to the beach so I could shoot some pictures for a video called "Small Synths in the Sand" but the wind, and the windblown sand convinced me not to bring my expensive camera to the sandblaster. It was so bad that just wandering the beach was not worth it, except for late evenings.
Attachments
Last edited:
That is a very good question, and one that literally haunted my dreams last night (ever dream about P-channel MOSFETs? I did!)
The pack I'm using has built-in balance protection. Used with the factory charger and the tool it was designed for, it also has overcharge and overdischarge protection. But the tool manufacturer doesn't give you too many hints as to which parts of the protection are built into the battery pack, and which parts might be in the charger, or the tool itself.
Back in the early 2000's when I and other RC pilots began to use lipo packs in our electric model aircraft, there weren't any off-the-shelf safety circuits for use with lithium packs, so we mostly rolled our own.
A safety cut-off is a fairly simple circuit: a precision voltage reference, a comparator / opamp, and a P-channel MOSFET. The precision reference provides a fixed reference voltage to one of the comparator inputs. You divide down the battery voltage with a couple of resistors, and feed that to the other comparator input. As the battery voltage drops, so does the voltage it's providing to one comparator input; but the reference voltage doesn't change, so the signal to the other comparator input stays constant. Eventually the battery voltage drops far enough to cause the comparator to change state, and the comparator output then turns off the MOSFET, preventing any further current drain.
This won't protect against a dead short across the battery terminals (overcurrent is also dangerous for lithium batteries). But it will prevent over-discharge.
(Incidentally, for model aircraft use, you do NOT want a power cut-off, which would cause the pilot to no longer have any control over the model, leading to a crash. Instead of turning off all power, I built circuits that either turned on a loud beeper, alerting you to land immediately, or blocked the control signal to the motor speed control, causing the motor to stop, but allowing the servos that control rudder, elevator, and ailerons to remain operational. You could then glide your model to a deadstick landing. Just like captain "Sully" Sullenberger, except without the deadly threat to hundreds of lives!)
To my knowledge, overdischarging a lipo cell didn't cause a fire - but it caused internal damage, which made that cell likely to puff up and burst into flames the next time you tried to charge it.
The relatively simple fix is never to attempt to charge a cell that has already been overdischarged. Most (all?) lithium chargers have this feature built in now - they will refuse to charge a pack in which any cell is at a damagingly low voltage.
My experience was with lipo and LiFePO4 packs - so I don't know exactly what translates to li-ion cells and packs. However we know that today's li-ion cells are chemically identical to today's lipo packs, the only difference being the guts are rolled up and stuffed into a metal can instead of being left flat and put into a thin plastic pouch.
Lithium paranoia, as George put it, is why I was considering using a NiMH pack. I went to a Home Depot and hefted 16 NiMH AA cells (19.2 V nominal), and was put off by the rather considerable weight, as well as the relatively small capacity.
The only thing worse is lead-acid. In my twenties I had an old car with a weak alternator I couldn't afford to replace, so I used to pull out the (lead acid, of course) battery and carry it up the stairs to my third-floor college dorm to recharge it every few days. Just the thought of carrying that much weight up three storeys makes me tired now.
-Gnobuddy
According to Wikipedia, complete power failure on jetliners, requiring gliding, has occurred quite a few times over the years: List of airline flights that required gliding - Wikipedia
Not all those incidents had happy endings.
My experience at the RC flying field paralleled what happened in full-scale aviation: those RC pilots who had spent some time flying RC gliders made successful dead-stick landings, while the ones who had never practiced gliding their powered models, or flown gliders, invariably panicked and crashed as soon as they encountered power failure.
Back on topic, I still have to make up a little wire pigtail with Anderson Powerpoles on one end to mate with the battery pack, and bare wires at the other to mate up with the screw-down connectors on my class D amp board. As soon as that's done, I can test battery-only operation.
A couple of members of my weekly jam have already started talking about having an outdoor music get-together while the weather's good. I better have this thing ready to go fairly soon.
-Gnobuddy
Not all those incidents had happy endings.
My experience at the RC flying field paralleled what happened in full-scale aviation: those RC pilots who had spent some time flying RC gliders made successful dead-stick landings, while the ones who had never practiced gliding their powered models, or flown gliders, invariably panicked and crashed as soon as they encountered power failure.
Back on topic, I still have to make up a little wire pigtail with Anderson Powerpoles on one end to mate with the battery pack, and bare wires at the other to mate up with the screw-down connectors on my class D amp board. As soon as that's done, I can test battery-only operation.
A couple of members of my weekly jam have already started talking about having an outdoor music get-together while the weather's good. I better have this thing ready to go fairly soon.
-Gnobuddy
I think that one is pretty much limited to using some sort of modeling to achieve the Fender Princeton sound in a battery-powered amplifier; whether it be a pedal (as gnobuddy's "Joyo" or my Boss "Fender '59 Bassman"; or in the preamp of a small amplifier such as the Roland Micro Cube. Perhaps in a DIY approach with FETs. And then adding a Class-D eBay amplifier (cheap, light, small) power. BUt what about the speaker? Should it be Hi-Fi flat so as not to influence the sound already colored by the modeler? Or should it just be the best guitar speaker you can afford/fit? My thoughts wander to the aim of the modeler designer---does he model it to sound Fenderish with a Hi-Fi speaker or a guitar speaker? I am thinking that 95% of the market will NOT be using a flat Hi-Fi speaker, but a guitar speaker instead. They are selling to musicians, not audio aficionados. So I am thinking a guitar speaker will more likely produce the desired result. Some modelers have a selectable "speaker emulator" but most do not.
The original guitar speakers were just hifi speaker, there were no specially tailored speakers. They were designed for larger cabinets or sort of open back, hole perforations in a back panel. So the combination of suspension stiff enough to keep the speaker from farting out without the back enclosed volume to act as part of the suspension and the need for extended high frequency response (extended being relative) dictated a lighter cone. Jensen speakers of the time and what is known as the American sound is a more neutral sound as compared to the British sound.
I think you would be ok with a guitar speaker you like and adjust the tone control as needed. I don't see modern day hifi speaker as having the attack and response of a guitar speaker, they are just too tame.
I think you would be ok with a guitar speaker you like and adjust the tone control as needed. I don't see modern day hifi speaker as having the attack and response of a guitar speaker, they are just too tame.
I take it your Boss pedal doesn't include any speaker emulation? In that case, I tend to agree with Printer2 - my guess is you will prefer a guitar speaker. Otherwise things will probably sound pretty harsh and unpleasant as soon as even a little overdrive enters the picture. Even purely clean tones may have "sizzle" or "ping" on top of them because of the (unwanted) extended treble response of a flat-response speaker.
I have a Digitech Trio+, which, among other things, acts as a semi-intelligent drum machine. You can route the drum sounds either to a guitar amp (along with the guitar signal), or through a separate output jack to a flat-frequency-response mixer / P.A.
When using the Trio+, the drums sound much better, more realistic, with more thump, kick, tightness, and crispness, if you use the second option and feed them to a flat-response amp/speaker. If you feed the drums into your guitar amp, they sound about as bad as those early drum machines from the 1990s, complete with soggy and lifeless-sounding kick drums and mushy cymbals.
It's quite striking to hear the difference - it really drives it home that electric guitar amps are not anywhere close to flat-response. We may like them with guitar, but that's pretty much the only thing they're good for.
-Gnobuddy
OMG, ur right!
Maybe they both traced the same counter-top corner??
Low-NFB exposes the basic nonlinearities which tend to be very predictable, rising as the appropriate power of level. So two to four (depending how many harmonics become significant) line-segments, not a circular arc. You also normally find narrow zones where 4th "cancels" 2nd and computed THD dips. But of course in days before universal air-conditioning and automated test processes, nobody would slave over a hot amp to get a truly accurate plot. Take a few points, trace a soup-can rim through them.
I just hooked up the battery pack to the class D board for the first time, and did a quick test with my beater Epiphone. So far, so good - no sparks, no flames, and everything works exactly as it did when powered by the 24 volt SMPS plugged into the wall.
The battery pack - currently half-charged - measures about 17.8 volts, so there will be some drop in maximum power output from the class-D board. But I'm nowhere near max power right now - it's night time, and I live in an apartment with neighbours living on two sides as well as overhead.
One of the reasons for using the Anderson's Powerpole connectors on the battery pack is that it can be unplugged from my amp and removed for charging - which will be done with the stock charger, outdoors on the ceramic tiled patio, inside a stainless-steel trashcan, with a Ziplock bag full of sand placed on top of the pack.
Powerpoles are rated for 10,000 plug/ unplug operations, so I have one less thing to worry about. A worn connector shorting out is the last thing you need on a li-ion or lipo pack. (There are some other commonly used power connectors that short momentarily every time you plug/ unplug them, and others that are extremely prone to short because of closely spaced metal contacts with no insulation in between them.)
Lithium paranoia? Yup, like George, I too have a full-blown case of it!
-Gnobuddy
The battery pack - currently half-charged - measures about 17.8 volts, so there will be some drop in maximum power output from the class-D board. But I'm nowhere near max power right now - it's night time, and I live in an apartment with neighbours living on two sides as well as overhead.
One of the reasons for using the Anderson's Powerpole connectors on the battery pack is that it can be unplugged from my amp and removed for charging - which will be done with the stock charger, outdoors on the ceramic tiled patio, inside a stainless-steel trashcan, with a Ziplock bag full of sand placed on top of the pack.
Powerpoles are rated for 10,000 plug/ unplug operations, so I have one less thing to worry about. A worn connector shorting out is the last thing you need on a li-ion or lipo pack. (There are some other commonly used power connectors that short momentarily every time you plug/ unplug them, and others that are extremely prone to short because of closely spaced metal contacts with no insulation in between them.)
Lithium paranoia? Yup, like George, I too have a full-blown case of it!
-Gnobuddy
I watched the house I live in being built. Other than the cinder block walls for the underground part of the basement the entire house is made of wood, styrofoam, plastic and sheet rock. One little oops can really ruin your day.
Lipo's live in ammo cans stored on concrete, and the LiFePo4's (considered safe) are stored in ammo cans.
We have all heard the stories of lithium based batteries burning up cars and even a house or two. Most of these come from the model helicopter / aircraft hobby where the rules weren't always followed.
I was present during some unsanctioned testing where bullets penetrated cell phones to see what happened. At least a dozen phones were shot and only one burned. It would have destroyed a purse or burned your butt if it was in a pocket.
A bullet through a 22 volt 5500 mAH Lipo pack of questionable quality (only made about half rated capacity) provided enough flames, smoke and stink to have torched a car. It was Ty Wrapped to a pine 2 X 4 which burned.
I was at a hamfest yesterday. A vendor was selling ammo boxes with batteries and charging circuits inside. Some even had ham radios installed. All of these used lead acid gel cells and thus were quite heavy. Judging from their other items for sale, these were intended for the prepper market where weight is not a prime factor.
Quicksilver Radio | Ham Radio Store
Quicksilver Radio | Ham Radio Store
The idea might be valid though. It could be possible to build such a box with LiFePO4 or even Lipo cells such that it was light enough to be portable. Substitute an inverter and a 120 volt outlet for the radio equipment for a UPS in a can.
Based on the single flaming helicopter battery that I watched, I would guess that a heavy steel ammo box would have contained the fire it made. Would that always be true?
When I lived in Florida and often rode my bicycle to the nearby park where all manner of flying craft were flown, the "best practice" for Lipo batteries was to store them in ammo boxes, and charge them in individual ammo boxes. The only stories I heard involving flaming batteries involved crash damaged batteries or the crash itself.
People seemed more concerned with the nitro based fuels used in "gas" powered craft. That stuff is Nitromethane, alcohol and castor oil.
Quicksilver Radio | Ham Radio Store
Quicksilver Radio | Ham Radio Store
The idea might be valid though. It could be possible to build such a box with LiFePO4 or even Lipo cells such that it was light enough to be portable. Substitute an inverter and a 120 volt outlet for the radio equipment for a UPS in a can.
Based on the single flaming helicopter battery that I watched, I would guess that a heavy steel ammo box would have contained the fire it made. Would that always be true?
When I lived in Florida and often rode my bicycle to the nearby park where all manner of flying craft were flown, the "best practice" for Lipo batteries was to store them in ammo boxes, and charge them in individual ammo boxes. The only stories I heard involving flaming batteries involved crash damaged batteries or the crash itself.
People seemed more concerned with the nitro based fuels used in "gas" powered craft. That stuff is Nitromethane, alcohol and castor oil.
I remember someone conducting a series of tests on lipo packs, and posting video and text results. He deliberately overcharged each pack to start a fire under controlled conditions.
He found the violent gas expansion that goes with a lipo bursting into flame was hard to contain - if put in a fully sealed container, anything bigger than a small lipo pack would blow the lid open when it caught fire. It's been some years, but my memory is that he tried both ammo cans, and small portable safes, and the lids were blown open in both cases.
That led to the "Ziplock bag full of sand on top" idea. Even if the lid blows open, the hope is that the sand will arrest the spray of white-hot debris, which is what starts ancillary fires. Additionally, the sand will help to smother the flaming debris it contains. Hot gases will still vent right through the sand.
At one point I obtained a damaged lipo pack from a crash-prone RC pilot friend, hooked it up to a long cable, placed a Ziplock bag on top, and set the pack on fire by deliberately applying overvoltage from an adjustable power supply. This was done outdoors, with nothing flammable for at least 10 metres / 35 feet in every direction. The Ziplock bag of sand did indeed work as expected - there was the usual cloud of stinky black smoke, but no spray of hot particles.
I couldn't get ammo cans, so I used a small fireproof safe to transport my Lipo packs. It is likely the lid would have blown open if a fire started, but it is relatively unlikely a pack will burst into flames while being transported inside a safe - flames usually happen during charging, or, as George says, immediately after a large physical impact (crashed model plane.)
I did my charging in the centre of a concrete brick (breeze block), with a concrete paver underneath, and another one on top. And, of course, a Ziplock bag of sand on top of the battery. The brick is cheap, fireproof, and not sealed, so no dangerous gas pressure build up in case of a Lipo fire.
My fellow RC pilots weren't so lucky. Three of them experienced in-vehicle Lipo fires, resulting in two totaled vehicles, both burned to a charred shell. The third car (a Toyota pickup, actually) should have been totaled, but wasn't, because the owner had no comprehensive insurance and did not report the incident to the insurance company. Virtually the entire interior on the passenger side was burned away, the dash was melted, the interior stank badly, but amazingly, the vehicle remained drivable.
One of the things I always found odd was how hard the glow-powered pilots had to work to start their engines. When you hear about the ingredients in the fuel, one expects it to be so volatile it catches fire at the slightest excuse - but I have frequently seen glow pilots spend up to an hour just trying to start their little engines, while those of us who flew electric put in four or five flights and stopped for a coffee break.
There were a few people flying actual gas(oline) powered aircraft. These were invariably giant-scale aircraft - quarter scale or bigger - and the engines usually stated out as weed-whacker or lawnmower engines, which had been modified a little to accept a propeller and mount into a model aircraft.
The big motivation to fly a gas engine is the much lower cost of gasoline (compared to glow fuel), but the engines are too big and heavy for anything but big (and extremely expensive) models. Those models are far too big and dangerous to fly at a public park, and should only be flown at a proper AMA regulated model aircraft flying field, with the pilot carrying appropriate insurance against any damage to property or injury to people caused by the model.
-Gnobuddy
Well, I'd say that between gnobuddy and tubelab, I am now scared shitless of rechargeable batteries.......The Lithium ones burn your house down, and the NiMh ones are never ready when you need them. So it's either just bite the bullet and spend ~0.50/hour for alkaline or go with LiFePo4. Eh?
I did buy a complete set for e-bike, i.e. a 36V/10Ah Li-Ion-accu with BMS including over-/ undervoltage protection, a LED "fuel gauge", a charger and a electrical termination plate / mounting unit. As these things work in e-bikes all over the world I am not too scared.
With 36V and a fully bridged class-d-amp you achieve some 50Watts per 8 Ohms speaker.
That comes pretty close to summing it up for me!
There's this whole thing about managed risk. We drive on public roads with thousands of other cars - the probability of a crash is relatively low (you may go many years without a crash), but the damage in case of a crash is likely to be very high. At the same time there is high incentive to drive (it allows us to do a lot of things.) So we manage the risk - we need official licenses and insurance in place to participate in this risky activity.
At the other extreme we have risks with a high probability (you will probably spill some food every now and then), but the amount of damage is likely to be relatively low (at worst, you stain an expensive rug or carpet.) The overall risk is not big enough to warrant a lot of management, so we eat and drink without needing an official license, or having to buy food-spillage insurance.
The question is where the risks for Lipo / Li-ion packs in the home or car fall. If you follow all the rules, and use the proper equipment, and the manufacturer didn't make any mistakes, the probability of a flaming battery pack is not very high (though the recall of a million+ devices in a single year shows the probability is not extremely low, either.) But if a fire does occur in your car (or worse, your house), the damage could be very bad - anything up to the entire cost of your house, or even worse, loss of life of a family member.
I'm actually surprised that neither the cellphone industry, nor the insurance industry, has stepped forward to offer insurance policies indemnifying against the eventuality of your phone / tablet / laptop computer battery bursting into flames and destroying your device / car / home.
I'm curious whether a typical home fire insurance policy will pay out if your house burns down because of a defective cellphone battery, or whether they will tell you to take it up with the cellphone manufacturer.
Now consider the additional factor of DIY. What are the chances a home fire insurance policy will pay up if your house burns down because you built a DIY electronic device with a lithium battery, and it caught fire?
My guess is, slim to none.
-Gnobuddy
My wife worked with a woman who was half of this company, her husband is the guy holding the large jet. Jets are cool, and loud.....but no batteries.
Mini Hobby ATL, Inc.
They flew these things at a county park which was near to where I lived. It was an uncontrolled field at the time, but has recently been rebuilt and is now an AMA field. The park is on the edge of the everglades swamp surrounded by swampland and an intersection of two interstate roads with a local expressway. The paved runway is visible in the southeast corner of the park. The shooting range takes up the north end. There used to be large outdoor rock festivals there many years ago. The house where i lived is in the northeast corner of the picture near the post office.
Airfield
The Markham Park airfield offers more than 50 acres of ground space for takeoff and landing of remote-control model planes and helicopters. With the recently extended and renovated runway, this airfield is one of the finest in the country! Numerous events are hosted throughout the year by the various clubs and organizations affiliated with the park. An Academy of Model Aeronautics (AMA) and a Markham Park flying card are required to fly at the field. Here is information on drones.
Attachments
Combining the two, RC skeet shooting. Foam core wings baby! YouTube
Last edited:
I flew at a field like that in Southern California - RC field on one side of the wall, shooting range on the other. Loud intermittent gunfire the whole time your model is in the air, very stressful for me and the exact opposite of that peaceful "in the moment" feeling I normally had when flying RC.
I only flew at that field one time - never again!
-Gnobuddy
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.