Changing a 2-wire 'integrated' trigger strobe tube with a 3-wire tube

Discussion in 'General Electronics Chat' started by raphidae, Jul 21, 2010.

  1. raphidae

    Thread Starter New Member

    Jul 21, 2010
    I'm currently restoring a lightbar (Federal Signal StrobeHawk). This lightbar normally has clear strobe tubes in them in combination with colored domes. I would like to use clear domes with colored strobe tubes.
    The problem now is that the only colored strobe tubes with the same ratings I could find have a three-wire connection (anode, cathode & trigger) whereas the old tubes are of 'integrated trigger' type.

    Picture of the old tube in the socket
    Picture of the new tube

    So I'm assuming I'll have to either build a trigger circuit to use the new strobes or rip out what's integrated in the old ones and use that (I prefer the first solution).

    Apparently pinouts for the original tubes are nonexistant (Whelen 'UNI' strobe (picture), it uses an 8-pin vacuum tube connector. I have taken one apart to see what's 'integrated' and how it's connected:

    The power supply is also kind of a black box to me as Federal Signal has no wiring diagrams on it, it provides a black and red wire for the strobe tube and that's it. I have tried measuring voltage between these two wires, and it seems to pulse too fast for my multimeter to measure anything useful other than that the voltage goes up when the tube is supposed to fire.

    The red wire goes to the anode of the strobe tube and the black wire goes to the cathode. Then there's what probably makes up the integrated trigger: a blue unmarked little component with two wires at the bottom, one of which connects to the red wire/anode as well and the other connects to the black wire/cathode with (what I think is) a capacitor (markings: NAP/104K/630V). The resistance between the bottom wires of the blue thing is negligible, so I guess this is a coil. The top wire connects to the trigger wire around the tube.

    Now, please correct me when I'm wrong, I'm guessing that the powersupply puts voltage across the black and red wires and thus the anode and cathode. Then at the same time it starts charging the capacitor through the coil so some current flows through it, creating a potential of the couple of thousand volts needed at the trigger wire to ionize the xenon gas in the tube, making the tube fire.

    In that case the blue component would be just a transformer with one end of the secondary winding connected to the trigger wire and the other end to nothing (or to somewhere else via a >20 megaohm resistor that I can't measure). And the specs of the capacitor would determine fire length and speed (in that case it's logical that the capacitor is not integrated into the tube, but soldered on the socket).

    That would also mean that the tube will just keep firing as long as voltage is supplied (assuming that a fire also discharges the capacitor), making the powersupply decide when the tube fires by simply turning power to it on and off. With the new 3-wire tubes I think the idea is to keep the voltage over the anode and cathode constant and trigger a flash when desired using the trigger wire. Can someone confirm that? If that's true, would the new tubes suffer in any way by not having a constant voltage over the anode and cathode?

    I've thought about just ripping the blue thing out and connecting the new tube using that in the same way, is that a good start? Or could I replace the blue thing with such a component without problems:

    In any case I'd like to know what these components are and how they work exactly and whether there are any pitfalls in changing these tubes. Any insight would be appreciated, thanks.
    Last edited: Jul 21, 2010
  2. raphidae

    Thread Starter New Member

    Jul 21, 2010
    I've made a diagram of how I think it's put together:

    Code ( (Unknown Language)):
    2.                                      __________________________
    3.                                     (             trigger wire
    4.                                     (
    5.                                     (
    6. red wire                            ( trigger coil
    7. __________________________________  ( secondary
    8.               |                   ) (
    9.               |      trigger coil ) (
    10.               |           primary ) (_________________ (to ?)
    11.        anode ---                  |
    12.               V                 -----  trigger capacitor
    13.      cathode ---                _____  0.1uF, 10%, 630V
    14.               |                   |
    15.               |                   |
    16. black wire    |                   |
    17. ______________|___________________|
    19. Or the same with the connector in the diagram:
    21.                                                  ___________________
    22.                                                  |                 |
    23.                                                  |                --- anode
    24.                                                  |    _____________V
    25.                                                  |   (  trigger   --- cathode
    26.                                   connector      |   (             |
    27. ___________________________________8 - 8_________|   (             |
    28. red wire                    |______7 - 7___________  (             |
    29.                                   _6 - 6_    pri   ) (             |
    30.                       _____________5 - 5____ coil  ) (             |
    31.                       |           _4 - 4_  |_______) (             |
    32.       trigger cap   -----         _3 - 3_            (_____(?)     |
    33.    0.1uF, 10%, 630V _____   _______2 - 2___________________________|
    34. ______________________|_____|     _1 - 1_
    35. black wire
    I'm thinking that the other end of the secondary winding (to ?) should be connected somewhere, possibly simply to ground, but this connection must then be internal to the trigger transformer (as it has only three wires) and I'm not measuring any connection from the trigger wire to the other wires, so if it's connected to one of those it must be via a resistance >20 megaohm (the max my multimeter will handle). Trigger coils I can find on the internet also have three pins only, but in this configuration:

    Code ( (Unknown Language)):
    2.                      __________________________
    3.                     (             trigger wire
    4.                     (
    5.                     (
    6.                     ( trigger coil
    7. __________________  ( secondary
    8. +                 ) (
    9.      trigger coil ) (
    10.           primary ) (
    11. __________________|_|
    12. -
    If that was the case here I should be able to measure the connection.
    Last edited: Jul 22, 2010