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Lighting up a lot (50!) vacuum tubes

  1. May 2, 2009 #1
    Hi! I'm an artist with a basic knowledge of electronics. "Basic," meaning that I can lay out a sorta-complex schematic on protoboard and solder it up, as well as test it and debug it if it doesn't work (given many hours and some alcohol to stem the frustration). As for actually understanding how the physics work, I'm a bit limited when it comes to that. I can do the math, provided you give me equations, but that's about it.

    So, with that in mind, I have about 50 or so vacuum tubes. I want to use them to get some nice glowy lighting effects in a stop-motion animation piece I am working on. I've managed to get every tube to glow by itself, but each one requires (pretty much) 6-12 volts, and they max out the current on all my power supplies, the highest of which seems to go to 5.5 amps. (This confuses me, because the meter says the max is 5.5, but where I've plugged the probes in, the label leads me to believe that the max is 0.5 amps. http://farm4.static.flickr.com/3572/3442815411_26db4c4e6c_o.jpg" It's the blue heathkit one.)

    On another supply that I do not have an image of, the tube pegged the meter at 1.5 amps. It glowed nicely though, so I calculated that in order to get 50 tubes to glow, I'd need about 75 amps (50 tubes * 1.5 amps = 75 amps total). Provided my math is correct, that's a lot of amps. I've looked into AC to DC converters that give me 12 volts at 100 amps, but those things are like $300 at the cheapest.

    My question to you guys is this: is there a cheap / free way to get 75 amps out of the wall and into 50 vacuum tubes?
    Am I lighting the tubes up correctly, or is there an easier way than just connecting the two filament/heater pins to a power supply? Also, I'm willing to use maybe 20 tubes or so. so that's like 30 amps.

    PS: please don't give me visual alternatives to using a boatload of tubes. If this doesn't work out, I already have a list of alternatives (christmas lights, drilling and shoving LEDs into the tubes, ect)
     
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. May 2, 2009 #2

    vk6kro

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    You might be able to get someone to help you do this safely.

    If you put vacuum tubes with equal current ratings in series you could put about ten 12 V valves across 120 volts AC from the wall socket.
    That would be 1.5 amps
    You could have 5 sets of these strings of 10 valves in parallel. 50 valves.
    That would be 7.5 amps.

    However, this must be done VERY carefully and it doesn't sound like you have enough experience to do it safely. So please get help.
    You should pay an electrician to do it and make it safe.
     
  4. May 2, 2009 #3

    MATLABdude

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    Can you reverse-bias vacuum tubes with 170 Vpk? Or over-volt them? I suppose that could be somewhat fixed by using a bridge rectifier, but I'm not sure about the overvolting part. Maybe a few 10:1 transformers to bring the voltage down to 12 Vac, but getting ones beefy enough to do it would probably cost more (in total) than the power supply the OP was looking at.
     
  5. May 2, 2009 #4

    dlgoff

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    If all you are wanting to do is to light up the filaments (heaters) then use a transformer that provides the proper filament voltage. Typically they need 6vac or 12vac. You can tell by the tubes number. e.g. a 6AW8 has a 6volt heater (http://www.oddmix.com/tubes/6aw8a_2.html" [Broken]). Note that the heater currents for these two are 0.6A and 0.15A respectively.
    For other tubes, see: http://www.oddmix.com/tubes.html"

    So just parallel up all the 6 volt filaments on a 120/6 volt transformer and all the 12 volt filaments on a 120/12 volt transformer.
     
    Last edited by a moderator: May 4, 2017
  6. May 2, 2009 #5
    If the heaters of those tubes are only 600 and 150mA respectively, why do they peg my power supply's current output meter? Is this because the supply gives them 12vdc, instead of 12vac? Or, if I current limit them, will the filaments still light up, so long as I give them time to warm up?

    @vk6kro: yeah, I'm not about to touch wall power without getting one of my electrical engineering friends to do the dangerous stuff for me.
     
    Last edited by a moderator: May 4, 2017
  7. May 2, 2009 #6
    Some tubes like 12AX7, 12AU7 etc can be run on either 6.3 or 12.6 volts because they have two filaments. Tubes running at the same voltage often draw different currents, so if you connect any tubes in series, match the currents.
     
  8. May 2, 2009 #7
    So, if I have 3 tubes, and two of them are rated for 0.6A and the other is 0.3A, I shouldn't put them in the same circuit?
     
  9. May 2, 2009 #8

    dlgoff

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    If they all have the same heater voltages then parallel them all together. Just add up the individual current rateings to see if your transformer can supply that current.

    Your power supply is only good for 0.5 amp on the 0 to 20 volt output.
     
  10. May 2, 2009 #9

    vk6kro

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    The resistance of valve filaments is quite low until they draw enough current to cause them to get hot. So, they tend to draw a large startup current.

    If you are using large transmitting tubes, quite large currents could be needed.

    If you put tubes in series, they will all get the same current, so this needs to be measured or looked up before you do this. (if you get it wrong, you can blow up filaments). You can put them in parallel if they have the same voltage ratings.

    So, you will need a supply that can give you 6 and 12 volts at up to 5 amps. Or, you could try to find data on each valve by searching for its type number from Internet.
    Tubes numbers sometimes give you information about the filament voltage. 6..... means 6 volts. 12... means 12 volts. This does not apply to transmitting valves.

    If you put 12 V on a 6 volt filament, it may blow it up, so it is better to start low and observe the brightness of the filament as you increase the voltage.
     
  11. May 3, 2009 #10
    Wow, thanks for all the help!! I wasn't expecting such fast and knowledgeable replies! I just wish I could return the favor with more scientific knowledge :P

    So with my new understanding of my power supply, I've measured the following:
    Code (Text):

     7 24V Tubes: 3.05A total
     9 17V Tubes: 4.20A total
     5 12V Tubes: 2.10A total
     4 10V Tubes: 1.50A total
    10  6V Tubes: 4.00A total
    I have a bunch of computer power supplies, so I'm thinking I can just use LM317 regulators to get the voltages I need.

    Thanks again for the help!! I'll be sure to post a link to the video of the final result!
     
  12. May 3, 2009 #11

    vk6kro

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    Computer power supplies produce a range of voltages, but only the 5 volt one is capable of a lot of current. Mine, here, gives 5 Volts at 30 Amps , but only an amp or so at 12 volts

    If you have access to a battery charger as used to charge car batteries, that would have fairly useful transformer in it, but you would have check it out to see if it was suitable.

    You have friends who can advise you so you should ask them to help with anything that takes you near mains voltages.
     
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