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Re: Regen built using Voltage Fluorescent Devices (VFD's) Update.

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  • Des
    Hi again Hue and happy new year, Hue wrote: Who will be the first with a VFD hi-fi music amp? ***** Not sure about the hi-fi aspect but this chap (link below)
    Message 1 of 9 , Jan 1 8:17 AM
      Hi again Hue and happy new year,

      Hue wrote:
      Who will be the first with a VFD hi-fi music amp?
      *****

      Not sure about the hi-fi aspect but this chap (link below) made a
      headphone amplifier using a VFD...

      http://www.5volt.eu/archives/62

      Looking at the biasing I dont think it will be very hi-fi though :-)
      Its interesting because he uses the VFD in pretty much the same way it
      would be used as a display except he AC couples his AF signals to the
      positively biased grid. The positively biased grid also means grid
      current, this might be OK for TX applications but for small signal
      applications I found the negatively biased or zero biased grid works
      better. It gives higher impedance and less loading on tuned circuits.

      Hue wrote:
      should i still connect all the anodes together (for one number display
      ***

      Yes, that way you can tell at-a-glance if all the segments are working
      though I have not seen any VFD's (yet) with faulty segments. I have
      seen quite a few VFD's with some segments much less bright than others
      and have concluded this may be due to long service.

      I have seen quite a few ex-VCR clock displays which are very "dim" and
      suspect this is due to the long hours of service. So far I have
      avoided using displays which are dim but with hindsight this may be a
      mistake. With a dim display I assumed the emission might be low and
      this may indeed be the case but thinking about it some more I realised
      it might just be burnt or worn out phosphors. If this is the case then
      a dim display might still be perfectly serviceable for a regen
      receiver or other non VFD application.

      Hue wrote:
      Also, how do single elements of a number fail? Is it the actual
      display decaying or of some driver transistor?
      *****

      So far all the faulty segments I have encountered have been due to the
      driver electronics failing but connecting all the anodes/plates
      together will confirm if all the segments are good. I like to join all
      the anodes/plates together because I feel it spreads the load and
      plates evenly.

      Just out of interest I have been experimenting with split
      segment/anode/plate configurations with interesting results.

      BTW are your VFD's single tubes or is it a multi-digit display? Good
      luck with the VFD project Hue and please keep us informed of your results.

      Best wishes,

      Des.

      --- In regenrx@yahoogroups.com, Hue Miller <kargo_cult@...> wrote:
      >
      >
      > Des, i think i have found a candidate here. It's a portable telephone
      > cable tester by H-P. When i opened it, i saw inside a warning about HV
      > up to 200 volts; i also saw a transformer and power transistors that
      > are possibly an inverter from the 12v battery supply; so this may be
      > a VFD display. One thing though, when i powered this thing up, not
      > all segments on the numbers displayed. If i try to use this anyway,
      > should i still connect all the anodes together (for one number display,
      > that is? ) Also, how do single elements of a number fail? Is it the
      > actual display decaying or of some driver transistor? Do the number
      > segments tend to fail after some time, in these VFDs?
      > Tnx- Hue K7HUE
      >
      >
      >
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >
    • John Rehwinkel
      ... VFDs are not normally run on such voltages. Their usual operating voltage is 20-30 volts, with positive grid drive. They light up nicely that way
      Message 2 of 9 , Jan 8 3:06 PM
        > Des, i think i have found a candidate here. It's a portable telephone
        > cable tester by H-P. When i opened it, i saw inside a warning about HV
        > up to 200 volts; i also saw a transformer and power transistors that
        > are possibly an inverter from the 12v battery supply; so this may be
        > a VFD display.

        VFDs are not normally run on such voltages. Their usual operating
        voltage is 20-30 volts, with positive grid drive. They light up
        nicely that way (saturated), but they're not very linear amplifiers.
        The 200 volt supply and slight negative grid bias makes 'em more
        useful as amplifiers, but most devices using them only want easy low
        voltages and a bright display.

        I suspect you have a plasma or panaplex style display there. One
        giveaway is the color. If it's a red/orange color, it's likely
        plasma. VFDs tend more to the green/blue spectrum, although some have
        different color phosphors.

        > One thing though, when i powered this thing up, not
        > all segments on the numbers displayed. If i try to use this anyway,
        > should i still connect all the anodes together (for one number
        > display,
        > that is? ) Also, how do single elements of a number fail?

        With VFDs, this rarely happens inside the display, but as you
        surmised, the driver electronics or a loose connection could easily
        cause this. VFDs wear out by getting dimmer, as the phosphor wears
        out and the filaments lose emission. But even very weary ones will
        still glow some. I suppose eventually the filaments could burn out,
        but in my experience that only happens when I hook the filament to the
        plate supply and burn it out white hot (actually I've never even
        managed this, every time I've made that mistake, I yank the wire when
        I see the brilliant filament and the VFD still works afterward).

        – John R.
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