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Filament voltage standards for tubes (valves)

Discussion in 'Electrical Engineering' started by Roby, May 3, 2005.

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  1. Roby

    Roby Guest

    Anybody know why there were different filament voltages for rectifiers
    (5 volts) and various small-signal tubes (6.3 or 12.6 volts).

    Why didn't one size fit all?

    Roby
     
  2. John Gilmer

    John Gilmer Guest

    That was back in the West Street era. That must have been a fun place to
    work back then. Just a few minutes by subway to the Theatre District.
     
  3. Popular in Europe (don't know about US, 120V would be a problem)
    were the 300mA heater tubes/valves, which were all designed to
    run in series (part numbers all starting 'P'). TV sets with perhaps
    15 tubes had them all in series across the mains, with a power
    resistor to make up any difference between the mains voltage and
    the total heater voltage and a thermister to limit the inrush
    current. Different sized tubes/valves used different voltages,
    so that the power required was delivered from the 300mA current.
    There was also another standardised current which I don't recall
    clearly -- might have been 150mA, but the the 300mA ones were far
    more common in commercial products.
     
  4. For the European numbering, it's the first letter...
    'D' is 0.5-1.5V, 'E' is 6.3V, 'G' is 5V.
    For series operation, 'H' is 150mA, P is 300mA, U is 100mA.
    Or the older glass ones with just a G designation, which
    I once heard someone describe as "female form shape" ;-)
     
  5. Roby

    Roby Guest

    Gosh, it's great to learn there are other survivors who remember tubes!

    I saw a sample of undersea cable and a repeater at Murray Hill in 1965.
    I think the loss between repeaters was 60 dB. Is that correct?

    Roby
     
  6. Ben Miller

    Ben Miller Guest

    Before that, however, AC/DC sets used a string of 6 volt tubes with either a
    ballast tube or a resistive power cord to drop the remaining voltage.
    Ballast tubes ran VERY HOT! I have several sets with a 3-wire power cord.
    One hot wire has the resistance necessary to drop the filament voltage. The
    other hot wire is a normal copper conductor, used for the B+.

    Ben Miller
     
  7. I personally used a drug store tube tester as late as 1973. And I
    worked at a steel mill where the instrument shop kept a tube tester
    around till well into the 1990's, because there was at least one
    tube-based amplifier in the plant.

    Bill
     
  8. Don Kelly

    Don Kelly Guest

    And by that time you probably had to order your tubes from Russia! :)
     
  9. John Gilmer

    John Gilmer Guest

    The ones I remember did a lot more than that. They had a meter and at the
    minimum determined whether the tube could function at least as a diode.
    Some of the drug store types were equivalent to the testers used by
    servicemen.
    That seemed to be the folklore.
    Well, that partly explains how the Japs god ahead of us in consumer
    electronics. With reasonable quality control one should be able to mix and
    match.
    Aside from everything else, it's a lot quicker to just exchange tubes than
    plug in a tester and test the tube.

    If quality control was really that bad switching tubes could lead to nothing
    at all working.
     
  10. John Gilmer

    John Gilmer Guest

    73 was definitely toward the end of the tube era tube sets were still being
    made. The tube era was extended by a few years with the "compactron" tubes
    which had 3 or more sections and something like 12 to 18 pins or so. The
    tubes were a lot more reliable by then too. The life limiting factor
    started to be components (like caps or transformers) that were damaged by
    the heat from the tubes rather than the tubes themselves.

    As examples: I had a set last last from 1980 to about 2003. It had one
    repair when it was about a year old. It was mostly solid state but the
    picture sure wasn't.

    Likewise, I have a working microwage thats over 25 years old.
     
  11. Guest

  12. Jimmie

    Jimmie Guest

    Because tubes have a different sound than solidstate amps. I will not
    qualify as one better than the other but for the most part people just
    prefer the tube sound. In other words, there is a difference and a choice is
    made. This is more imporant in a guitar amp than in a hifi amp. In music the
    distotion is part of the sound that is desired, In Hifi there should be as
    little distortion as possible. The ctriterion for hifi can be meet with
    either tube or solidstate amp. For music where the distotion is much more
    pronounced the type of distotion is much more critical.
     
  13. keith

    keith Guest

    Teh technical term is "audiophools".
    They fail every double-blind experiment. ...worse than Randi doing Uri.
    Audiophools like the "warmth" of toobz. On a cold winter night I prefer a
    fire in the fireplace, but...
    One of the suggestions on sci.electronics.design was a "double-blind"
    experiment where a toob amplifier was recorded and played back through a
    decent SS amp (perhaps even with glowing filiments showing), and challenge
    the audiophools to tell the difference. Repeat experiment with black
    vinyl and CD. The fact is the ear isn't as good as either.
     
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