How to not die learning about high voltage tube audio amplifiers?

Discussion in 'Analog & Mixed-Signal Design' started by Dolmetscher007, Apr 14, 2019.

  1. Dolmetscher007

    Thread Starter New Member

    Mar 21, 2019
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    I would very much like to learn to design and build my own audio power-supply/pre-amp/power-amp... a P.A. System. I am a musician, and I have always been very interested in learning how tube amps work (both guitar, and P.A.'s). Now, I find myself in a situation where I really need a new P.A. I have the money to buy a P.A., but I'd really like to build one myself.

    I have found what seems like a really cool 1,000 watt audio amplifier project online. However, as I read about it... and actually as I read about any amplifier project, they all always say the same thing. They say something to the effect of, "Do not attempt to work on this project unless you are highly experienced with high voltage electronics, as this thing can and will kill you." I do not at all doubt it. Unfortunately, however, none of the website/forums/schematics/etc. that warn about killing yourself unless you are experienced with these things, never give any tips or advice on where or how I can learn exactly what not to touch.

    Do any of you guys know of a resource that specifically addresses audio amplifiers and how not to kill yourself?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    This a real hazard to one's health. Please take this advice very seriously.

    I was once working on a tube amp. The power was off and the cord was unplugged. The highest voltage while power was on was 350V.
    I can tell you that I don't know with what I came into contact. All I know is that I was flung across the room still sitting on the chair. I lived to tell this story.

    You have learn to walk before you can run. Begin with learning how low voltage circuits work (under 30V) before moving up the voltage scale.

    And the number one rule when working with high voltages is you keep one hand in your pocket. This is not a joke.
     
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  3. Picbuster

    Well-Known Member

    Dec 2, 2013
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    Depending on the type of amplifier and output power voltages could run above the 1000V.

    A one KW amplifier needs at leased 25% more energy from power source and could create a spark bridge to your body of parts thereof.

    The only way is, as Mrchips stated stay away with your hand in your pockets and start with a low voltage driven amplifier.

    Please stay away from that type of high voltage stuff and let us listen and enjoy your music.

    Picbuster
     
  4. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    I would recommend old textbooks that taught tube theory and or tube RF/radio theory.

    Have you searched for "safety practice for tube amplifiers"?

     
  5. crutschow

    Expert

    Mar 14, 2008
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    If you really want to build archaic tube amps, then start with a preamp that uses voltages less likely to be lethal. :rolleyes:

    I've worked with tube audio amps in my early years, and the best thing that every happened to them was the invention of the transistor, making tubes obsolete. Don't miss the heat, the dangerous voltages, the hum, and the huge audio transformers in the least. :D
     
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  6. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    I learned this as what was called "The Left Hand Rule". You always kept one hand in your pocket. Why? Because high voltage from hand to hand typically only happens once in your lifetime. And not because you learn your lesson but because of the high potential that your friends and family will be mourning the loss of an otherwise bright musician.

    Geez, I forgot about those things.

    One thing about those old analog amps, they DID produce a beautiful sound. I DO miss the analog music, but the digital is so much more convenient and easy.
     
  7. bertus

    Administrator

    Apr 5, 2008
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  8. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    I agree but there is something cool about rebuilding old tube amplifiers. When I worked for Hughes Aircraft we had a contract to rebuild Navy 1MC tube type PA amplifiers. Removing 30 years of dirt and nicotine by pressure washing the point to point wiring chassis, installing NOS tubes and replacing almost all the capacitors and resistors with modern parts resulted in an excellent sounding audio amplifier that was also nuclear EMP proof.. :D
     
  9. jpanhalt

    Expert

    Jan 18, 2008
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    That "theory" is based on poor reading (or not reading) the basis for the original recommendation and not understanding anatomy. The reason is that having both hands in a working area increases the likelihood of getting shocked hand-to-hand, just as using both feet in the working area would increase the likelihood of getting shocked foot-to-foot.

    From an anatomical standpoint, electrical current from hand-to-hand does not actually go over the heart; whereas, hand-to-contralateral-foot (e.g., right hand to left foot) probably does. Unfortunately, data on fatalities is highly skewed for those using both hands, because very few people who are right handed work concurrently with their left foot rather than their left had.

    A recent thread here gives a common reference by Bikson ( https://www.researchgate.net/public...ards_associated_with_exposure_to_low_voltages
    ) (https://forum.allaboutcircuits.com/...hru-bodily-tissues.158018/page-2#post-1372111 ) who reviewed anatomical relationships and shock fatalities.
     
  10. Audioguru

    Expert

    Dec 20, 2007
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    Since you said you will salvage the old parts from Navy PA amplifiers then the frequency response will be too narrow and the distortion will be too high for music.
    I built a kit hifi audio amplifier that used vacuum tubes about 57 years ago and it sounded pretty good for a few months when its output vacuum tubes wore out and needed replacement, over and over and over until I sold it to an old guy. I replaced it with a solid state audio tuner/amplifier that I still use today.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    There is a deep rooted misconception that tube amps sound better than solid-state amps.
    This misconception is straight forward and easy to understand.

    When a solid-state amp is driven to overload, the signal is clipped hard, resulting in square-waves with high harmonic content. The sound is harsh.
    When a tube amp is driven hard it distorts the signal in a non-linear way. This gives it a signal compression effect. The result is a more mellow tone.

    A modern solid-state amp can be modeled to reproduce the same distortion as that provide by tube amps, if that is what the musician desires.
    A modern solid-state amp uses digital signal processing (DSP) to replicate any kind of amp desired.
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    As said, the tubes need high voltage and will wear-out after some time.
    If you would have a look at this site:
    http://sound.whsites.net/projects-0.htm#pwr
    You will find schematics for transistor amplifiers fro 20 to 1500 Watt.

    Bertus
     
  13. Audioguru

    Expert

    Dec 20, 2007
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    If the musician plays a guitar, then I like to hear an unamplified acoustic one or one amplified by a hifi audio system.
    Electric guitars produce the buzzer type of sounds from overdriven and fuzzy tube amplifiers with their poor high frequency response producing muffled distortion.
     
  14. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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  15. Audioguru

    Expert

    Dec 20, 2007
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    Distorted and muffled sounds are noises, not music.
     
  16. Sinus23

    Active Member

    Sep 7, 2013
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    That is like saying words uttered under ones breath ain't words at all.
     
  17. Yaakov

    Well-Known Member

    Jan 27, 2019
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  18. jpanhalt

    Expert

    Jan 18, 2008
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    Good article. I particularly appreciated that it disclosed potential author conflicts:
    "John Atwood is a consultant on tubed audio design and owns One Electron Co., Santa Clara, Calif."
    http://www.one-electron.com/
    http://www.one-electron.com/Products/Trans/UBT1_20.pdf

    That does not negate the findings in any sense. But given that this is 2019, I suspect there are other research-supported viewpoints to consider.
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    I believe that that was not a valid and meaningful comparison of tubes and transistors.

    1) No mention is made on the initial harmonic content of the 1kHz test signal.
    2) Modern amplifier designs incorporate negative feedback which would totally alter the results.
    3) Modern amplifier designs almost always consist of more than a single stage Class-A amplifier.
     
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  20. Yaakov

    Well-Known Member

    Jan 27, 2019
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    It explains the historical affinity for tube amps, and shows there is a least a reason people could have that preference that is not their imagination.

    It’s not a definitive answer to the question today.
     
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