crazy ideas for a tube amp with many watts! - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: January 09, 2020, 08:05:26 pm
content: so I read about the fender 400ps and how it outputs a decent 435w RMS, so I then wanted to know. how much power can I get out of a tube amp before it starts to get really stupid, and yes I know 8 power tubes probably are stupid already,anyway, I heard Carlson talk about power tubes oscillating when there are many of them connected together in his "six-pack repair" video and how some amps put resistors in series with the plates to fix that.would this be a problem with 8 6550A tubes? and how would I fix that? I tried to find something about this on google but didn't find anything.also, are there more powerful audio output pentodes?also, I find many really cheap power and modulator tubes that have a plate dissipation of several hundred or even thousand watts, are there any that type of tube that can be used in an audio circuit or is that a dumb idea?also, I know I will have to get some custom output transformer that can withstand all that current.

author: woodchips
author_rank: Frequent Contributor
timestamp: January 09, 2020, 08:10:53 pm
content: Try valves like the 6080, lots around as used in Tek etc scope PSUs. Run them as cathode followers, at your power levels probably won't need an output transformer? A variac can make a good output transformer, adjustable too.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2020, 03:08:16 am
content: They made tubes up to 1.5 MW, watts are not a problem. Now, if you expect it to be compatible with a 120V 15A circuit, or 240V 7A circuit, don't expect more than about 800W real output (even for a solid state linear amp), more likely 400 or thereabouts (or about double that from a 240V 13 or 15A circuit, etc.). Probably the Fender example is such a case.What tubes to use? Doesn't much matter. 6L6s and the like (more or less including the families up to KT88s and such) are preferred for audio to begin with, and are cheap (relatively speaking) and plentiful in current production. 6080/6AS7 is hard to drive, more expensive(?), has lower plate dissipation, shorter load line (triodes have less power output than tetrodes), and consumes far more heater power. Sweep tubes are generally expensive, and offer high plate efficiency but only modest overall efficiency (again, heater power).Sweeps are generally quite powerful, especially when driven hard, as befits their original application. One could construct a class D tube amp, doing probably over 800W (from a 1800 VA circuit), with just a quad of, say, 6LF6 or 6LV6 or EL519 (or any of their series-heater brethren). The power density easily offsets the cost of obtaining these tubes. One might (rightfully?) question whether such an amp would be worthwhile, i.e. create "That Tube Sound", in the presence of so much distortion (PWM modulation is essentially "100%" distorting a signal plus carrier). Note, you still need an output transformer rated for the full signal bandwidth -- you don't get to save any transformer size with just PWM alone, not without a lot of extra work (see Dave Berning's DC transformer / chop-amp designs for example).Tube cost isn't a huge motivation, anyway; it is a maintenance cost, but the rest of the amp will easily cost upwards of $1000 to build or buy, too. The capital/operating cost tradeoff is a worthwhile concern here. One could go with NOS industrial or PQ types, derated modestly, to obtain a likely 10khr+ lifetime, versus cheap Chinese 6L6s that will wheeze out in a tenth of that time. Derating requires considering this in the design -- you might only need 8 x 6L6s if you're beating the shit out of them, but 10 or 12 might be needed to give adequate derating.Protection circuitry is a good idea regardless, as that beefy output transformer won't be something you want to melt from an errant sparking tube. Adequate fusing and/or supply limiting, and maybe bias servo control, are simple enough precautions.The power transformer doesn't need to be expensive, fortunately. A switching supply is very reasonable at this power level; of course, making one that operates safely and reliably without belching out EMI, may be best left to the professionals...Tim

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 10, 2020, 03:33:28 am
content: Tubes have limits, but one can go full forward with transformers using magnetic amplifiers. They are used in electrical locomotion, transoceanic transmitters, and WW2 cruise missiles. Also used to amplify music in most artful form, where just pure copper and iron do the work.http://www.auditorium-23.de/MagAmp/MagAmp.pdfI'd replace diodes with mechanical synchronous rectifiers and input tubes with smaller magnetic amplifier. Thus making multikilowatt amplifier with only copper and iron and nothing else.Edit: Also for speakers at bass, the highest acoustic power density can be reached by using rotating fans. Imagine steampunk civilization without vacuum or semiconductors or chemistry. Only metallurgy, magnets and silk fabric as dielectric. With only pure Electrical Engineers (zero electronics) the life and entertainment is still possible.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 10, 2020, 04:20:18 am
content: the Gi7bt datasheet says it is only 30W continuous output power. Or 11kW for 10useconds with 9kV at anode. So for musical performance longer than 10useconds at 1000W there should be 33 tubes involved, with forced air and 1.2kV anode at 150mA each. So 6kW of quiescent power.Considering power requirement at DC, the AC side should accommodate ripple current, so transformer is 10kW. I think this is a transformer size which is larger than common distribution transformer immersed in oil and placed on telegraph poles. It possibly will require small concrete foundation when placed stationary and will require building permit and fence and lock.

author: David Hess
author_rank: Super Contributor
timestamp: January 10, 2020, 05:46:45 am
content: Quote from: ELS122 on January 09, 2020, 08:05:26 pmPower costs money, how much do you want? It also costs a lot of weight and volume.QuoteThe same thing can happen with transistors. Each tube plate sees the other plates as loads and the plate loads include reactive components. The parasitic elements from the physical construction do not help.Dampening the reactive components can be done by adding series or parallel resistance. Notice that a tube amplifier can sometimes oscillate, perhaps destructively, if no loudspeaker load is connected. Adding series resistances to the grids could also suppress oscillation and is commonly done with tetrodes to suppress snivets where their operating point creates a negative resistance, aka tetrode kink, which is prone to oscillation.

author: Moshly
author_rank: Regular Contributor
timestamp: January 10, 2020, 07:44:42 am
content: You should sub to 'ElPaso TubeAmps'

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 10, 2020, 04:37:06 pm
content: I think the densiest power wise tube is 6C33C with very low anode voltage and 60W continuous power.Some amplifiers run it without output transformer. It can be more expensive, but less dangerous voltage wise.6C33C is may be even worthy to use in AC motor drives

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2020, 06:13:27 pm
content: There are forced air ceramic tubes doing 5kW in the same size as a 6S33S* and water cooled tubes doing >10x more than that...*Give or take how you like to transliterate; it's a Cyrillic 'C' which looks like a Latin 'C' but is actually 'S'. I see people writing things either way, so, just to make light of that.Tim

author: floobydust
author_rank: Super Contributor
timestamp: January 10, 2020, 10:38:11 pm
content: One big problem when you increase power by increasing voltage, is the output transformer's windings need very high voltage insulation. With 6550's it's maybe 1,200V but once you need say 5kV then the windings get too fat. Costs for everything go up.So the usual approach is to instead increase current by paralleling tubes, instead of using a big high voltage, high impedance tube.Hammond 1650Wgoes up to 280W ($330 28lbs) by going low impedance 1,900 ohms as if for 6-8 parallel tubes, like the Ampeg SVT approach.Another advantage staying with paralleling smaller tubes is the grid drive voltage does not need to be so large. Generating a clean 50Vpp signal for grid drive and 6550's is not that difficult butEimac 4-400Ais around 200V drive.The last thing to look at is speakers - if you have say a 1kW amplifier, then it gets complicated because loudspeakers don't really operate at this power level. Your typical 15" speaker maybe 500W tops. You remember what happens to Marty in Back to the Future at volume past 11...

author: Yansi
author_rank: Super Contributor
timestamp: January 10, 2020, 10:42:30 pm
content: Whats the point of having a guitar amplifier larger than 50W? Whats the purpose? Making the FOH/sound engineers pissed & angry?I have never understood this. It is the job of the sound crew to make things loud.

author: langwadt
author_rank: Super Contributor
timestamp: January 11, 2020, 12:28:00 am
content: Quote from: ELS122 on January 11, 2020, 12:08:29 amit's not the 1950's, being loud on stage just makes it harder to get good sound

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 11, 2020, 03:12:02 am
content: Quote from: langwadt on January 11, 2020, 12:28:00 amYou need to get louder, or else the audience will not hear you. Everyone in audience has a hearing damage loss from music being too loud, so you need to go louder.

author: langwadt
author_rank: Super Contributor
timestamp: January 11, 2020, 03:31:34 am
content: Quote from: unitedatoms on January 11, 2020, 03:12:02 amthat's what FOH is for, and around here all the live venues have voluntarily agreed to a max 103dBa 15 minutes at the mixer

author: woodchips
author_rank: Frequent Contributor
timestamp: January 11, 2020, 02:49:26 pm
content: The point about using cathode followers is that the signal is ground referenced. With a normal type amplifier the output is at the anode, and as has been mentioned is hundreds of volts up. So an isolating transformer is needed.The Variac is ground referenced, just adjust the tapping point to get the speaker impedance you want. I have seen 25V 6A Variacs, and at very high outputs a 110V one might do.Another possibility is the E12. All these valves designed as series voltage regulators have low anode cathode voltage, but lots of current.Experiment!

author: Yansi
author_rank: Super Contributor
timestamp: January 11, 2020, 11:04:37 pm
content: Nothing personal, but then you are the typical dumb guitarist, that is a pain in the ass to work with on stage.It is the job of the sound engineers / FoH to makes things loud and to set you up your monitor, so you can hear yourself. You use only such volume, so you can hear yourself on the stage. You absolutely do NOT want your amp to interfere with the main PA or pass excessive sound levels in front of the stage.Excessive volume on stage also annoys your band mates, that due to your stupidly loud amp stack can't hear themselves.If one can't hear himself on stage, the correct way to do it is to lower the level of OTHERS, not to add more volume to yourself.It is the classic "trash in - trash out".

author: langwadt
author_rank: Super Contributor
timestamp: January 25, 2020, 08:58:54 pm
content: Quote from: ELS122 on January 25, 2020, 08:43:08 pmbut why?

author: james_s
author_rank: Super Contributor
timestamp: January 25, 2020, 10:45:00 pm
content: Quote from: langwadt on January 11, 2020, 03:31:34 amI stopped going to concerts years ago because they're so obscenely loud. When it's so loud that it sounds like raspy distortion in my ears it's not enjoyable and I'd like to be able to enjoy music still when I'm 50. It really hit home when I was around my friend's dad, he was a home builder for years and was often using loud power saws and such, the guy can barely hear and without his hearing aids you have to yell for him to understand you. I've found concerts to be way, WAY louder than necessary to be plenty loud in all areas of the venue.

author: Trailboss
author_rank: Contributor
timestamp: April 20, 2020, 01:06:23 pm
content: Here is few things that make the Fender 400 PS unique and very powerful.Firstly it's rated power is at 50 Hertz, compare that to any other amp.To my knowledge it is the only amp that operates in AB2. I have worked on quite a few amps with six or eight 6550A's and they never made the power of a 400 PS.Transformer phase inverter allow grid current to allow AB2 operation. Tube phase inverters operate only up to the point where they cutoff into blocking distortion. The venerable SVT doesn't come close to the 400. I have three SVT's and a few 400's that I play, I like the SVT for some stuff I play but the pure tone of the 400 is unique. The 400 was also much more reliable than the SVT due to the fact that when pushed hard the plate voltage would drop below screen resulting in a unique light bulb effect in the output tubes! LOLThe 400 PS was designed around the GE 6550A.It's filament voltage runs at about 6.8 Volts.It is designed for 8 Power Tubes. The chassis has room for an additional pair of output tubes.The output transformer has Four separate secondary windings. The output pairs are cathode switched at the speaker jacks.It can be tough on modern tubes, I only run my 400's with GE tubes.Each output must load into four ohms or you may risk getting flyback which results in creating "Magic Smoke".Pick one up and modify it by adding the additional pair of outputs, get yourself four "W Bins", the original speaker. Lay the four W Bins down on their sides in a straight line stand about 40 feet away and play a low B and prepare to have your bowels loosened, I am not kidding.!Good Luck!

author: langwadt
author_rank: Super Contributor
timestamp: April 20, 2020, 01:27:39 pm
content: Quote from: ELS122 on April 18, 2020, 10:50:27 amhorse-drawn and powered by a coal fired steam engine to make a it a bit more modern ...

author: GreyWoolfe
author_rank: Unknown
timestamp: April 20, 2020, 03:39:25 pm
content: I know my ears are not the best anymore but that sounded absolutely horrible on the low notes. Muddy doesn't even begin to describe what I was hearing. Or, is it just me?

author: Yansi
author_rank: Super Contributor
timestamp: April 20, 2020, 04:06:29 pm
content: If you would mind reading the description of the video, you would know, that the sound played does not come from this amplifier anyway

author: jmelson
author_rank: Super Contributor
timestamp: April 20, 2020, 07:01:14 pm
content: Quote from: ELS122 on January 11, 2020, 12:08:29 amYup, I went to a Grateful Dead concert in 1969/70, and they were using the modulator out of an AM broadcast transmitter as an amp.They rolled out this thing with two huge glass bottles on it, and when they hooked it up they lit up and I immediately started stuffing paper in my ears. I'd guess at least 1KW for a minimal broadcast transmitter. They typically used the same tubes for the modulator as the RF final of the transmitter.Jon

author: Yansi
author_rank: Super Contributor
timestamp: April 22, 2020, 10:30:54 am
content: Quote from: ELS122 on April 22, 2020, 09:23:31 amWhy do you think so?And btw, I think that guitarists with >50W amps are all but annoying.

author: Yansi
author_rank: Super Contributor
timestamp: April 22, 2020, 11:02:50 am
content: You probably have turned smileys turned of, don't you?What in fact (jokes aside now, seriousface) is annoying is your constant switching of plans. It is impossible to give you any factually useful suggestions, as you don't even seem to be sure about what you want to do.So state clearly what you are after. State some specs of an amp you want to build and stick to it. Only then it is possible to start an engineering discussion. Otherwise probably not only me sees this topic as a way you are getting funny ideas that won't ever be recreated.I also get the idea from your constant target switching attitude, that you may have close to zero experience building tube amps. So you likely don't even know what you are getting into and you would likely better start with a small amp, like couple hundred watts and not 10 kW. It is a very difficult job to design a good high powered amp with semiconductors, let alone with this ancient vacuum tech.So, please, put down some design requirements: Output power, distortion / frequency range of interest , class of operation, topology (all tube or a hybrid) etc. Also maybe would be good to start by elaborating on what PA will it be used for, eg: Floor monitors for guitarists, or a front PA for an venue (how large then?) Do you need a full range amp or just for the mid-high?Budget is also a major constraint here, as there are zero to none off-the-shelf components available for such an contraption and the HT power supply and output transformer will cost some serious bucks for the power levels you are constantly joking about.Reliability is a concern too. The amp must be reliable if you would like to use it as an actual PA. Last thing you want is it failing in the middle of a performance.

author: TimFox
author_rank: Super Contributor
timestamp: April 22, 2020, 04:56:46 pm
content: One of the best high-power vacuum-tube amplifiers was the McIntosh MC3500 (industrial version MC350), rated at 350 Wmeanpower (not RMS power, as in the vulgar error). An interesting link ishttps://www.vice.com/en_us/article/ezv3ym/that-time-the-navy-used-the-grateful-deads-amps-to-listen-to-soviet-subswhich discusses the use of multiple amplifiers for the Grateful Dead and possible use in military applications. Besides the use of sweep tubes in parallel-push-pull, the key to such an amplifier is the output transformer.

author: OwO
author_rank: Super Contributor
timestamp: April 22, 2020, 04:59:53 pm
content: I didn't quite understand the discussion about guitar amplifier power on stage; is there like a separate amplifier/speaker on the stage (apart from the main amplifier/speakers for the audience?) Otherwise how do you get a big audience to hear you with only 50W of total power? I've never been to a concert so have no clue. If it's the former, why is a separate stage amplifier needed? can't the guitarist hear the main speakers? if not, why not have the guitarist wear some headphones so he can hear himself? An on-stage speaker just sounds like the recipe for feedback issues...

author: OwO
author_rank: Super Contributor
timestamp: April 22, 2020, 05:04:24 pm
content: Are high power amplifiers (>1kW) actually used at concerts? I've always thought they use "antenna gain" to reduce power distribution requirements. A big array of speakers (spaced apart) driven in phase will get the sound very far while also not sounding very loud for the audience in the front row.

author: langwadt
author_rank: Super Contributor
timestamp: April 22, 2020, 05:24:54 pm
content: Quote from: OwO on April 22, 2020, 04:59:53 pmThe guitar and amplifier is a large part of the instruments sound, and just like drums etc. it is miked up for the PA that the audience hears. There will usually also be monitor speakers or these days more often wireless earbuds with a separate mix for each member of the band

author: langwadt
author_rank: Super Contributor
timestamp: April 22, 2020, 05:31:33 pm
content: Quote from: OwO on April 22, 2020, 05:04:24 pmstacks of them, with electronic cross-overs and special equalizers and often extra speakers just for right in the front of the stage

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 22, 2020, 06:48:54 pm
content: Quote from: ELS122 on April 22, 2020, 09:23:31 amI once built a small class D tube amp. Single ended, 3.5W. Was a bit rough on the screen grid, but well within ratings otherwise. (I limited screen power to, I think, 4 or 5W, out of a 2 or 3W rating.)Single ended, means the equivalent circuit was a buck converter with load resistor. So the amplifier is "class A" overall, but the plate circuit is class D, about 80% efficiency.The modulator was surprisingly linear, for an RC ramp generator (astable multivibrator + comparator); I measured <3% THD up to clipping. Carrier 140kHz I think, output rise/fall time around 100ns. No global feedback. Quite low output impedance, since it's always either the plate resistance in saturation (~100 ohms), or the damper diode (~50 ohms). Quite good bandwidth, down to 10Hz into a 600 ohm transformer.I have plans for a proper (push-pull) one, which will do about 200W from a pair of sweeps. Just a very low priority project.Tim

author: Yansi
author_rank: Super Contributor
timestamp: April 22, 2020, 10:42:02 pm
content: Also interesting idea to consider: Instead of a textbook push-pull AB class, why not shuffle a bit and make it a circlotron? Would likely ease some troubles with the output transformer design. But would require two separate HT supplies, which I still see as less of a problem, than having a pretty damn high voltage swing at a high impedance ratio output transformer.//Output impedance of a circlotron is low, as the output is essentially a cathode follower