Dentron Clipperton "L" Linear Amplifier - Replacement bulb

Discussion in 'Amateur Radio Amplifiers' started by W9GB, Feb 20, 2011.

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  1. W9GB

    W9GB Ham Member QRZ Page


    CHICAGO MINIATURE Incandescent Lamps (Mouser catalog, page 111)

    Dentron normally used T-1 3/4 Midget bulbs at 14 Volts, either with a Screw base (Figure G) or Flange base (Figure H)

    1. Since these amplifiers are > 30 years old and used or silent key (estate) units are subject to unknown repairs by previous owners,
    Confirm the voltage used for the bulb.

    2. CM373 (Screw base) and CM330 (Flange base) are only rated for 1,500 hours of usage.
    That means the bulb only lasts about 1 year for 30 hours "on" each week (Green power light).

    3. CM8262 (Screw base) and CM382 (Flange base) are rated for 15,000 hours, but a bit dimmer (MSCP).
    The brightness of miniature lamps is usually measured as luminous flux using the unit lumen (Im).
    In the Anglo-American literature the unit “Mean Spherical Candle Power” (MSCP) is used. Both units can be related as follows: 1 MSCP = 4*pi*Lm = 12.57 Lm.

    If the the brighness of this indicator is not a concern, these 2 bulbs will provide years of operation/service (7 years at 40 hours "on" each week).

    Chicago Miniature - FAQ

    Technical Notes - Incandescent lamps

    Technical Notes - LEDs

    Chicago Miniature Lighting, LLC
    46615 Ryan Court
    Novi, Michigan 48377

    DESIRE an modern LED, instead of an Incandescent Lamp ??

    ChML provides standard and custom LED solutions for various automotive, aviation, military, appliance and electronic applications.

    Contact Ed Quinn (phone # 201-489-8989, e-mail: at ChML for more details.
    Last edited: Feb 20, 2011
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    The manual I found for the Clipperton L shows three pilot lights connected across the output of an unregulated halfwave rectified/filtered source that also powers the T/R relay. The "Operate" lamp is across the T/R relay coil. There's no telling what the voltage is but it'd likely be higher with less load on it... and the lamp life would be less. I suggest measuring the voltage to ensure it's not higher than the lamp voltage. If it is, there are many ways to mitigate it... series diodes/resistor, voltage or current regulator, or replace with LEDs.

    LEDs would last virtually forever but they can create a "spotlight" effect on the meters unless you use several smaller ones or fewer larger/brighter LEDs with a wide dispersion/viewing angle (and mount them not too close to the meter).

    I prefer the current regulator with incandescent lamps. Incandescents have a very low cold resistance and the filaments suffer mechanical shock when the voltage source has a lot of current available. This inrush current (5 to 15 times of a lamp's running current) as well as too much running voltage/current are the biggest causes of premature lamp failure. A current regulator solves the problem.

    The 373 & 382 run at 80mA maximum. The LM317L can be configured as a current regulator (up to 100mA) with one resistor. You just need 1.25V more on the input than the output if you want the lamps to run at rated voltage/current. If the current is set to less than 80mA, the lamps should last a very long time. The LM317T can handle all the lamps (the lamps need to have the same current rating).

    I've never had to replace the lamps in my SB-220 (I've had it since ca 1975). The lamps are 6.3V types (#47) that run on the 5V filament source. They're plenty bright enough.

    Attached Files:

  3. W8JI

    W8JI Ham Member QRZ Page

    The real problems with the lamps come from three things:

    Dentron bought lamps and other parts surplus from Electronics Surplus in Cleveland Ohio.

    They also spec'ed the transformers with 12 VAC windings with a 117 VAC primary in some and a 120 V primary in others, so when the the winding is rectified and filtered the 12 volt dc supply is close to 18 volts or even higher.

    Finally, all incandesent lamps over a few volts have shorter life on dc because of filament errosion. With a lamp the size and voltage of the Dentron, life is seriously shortened.

    I'd use a 24 volt lamp.
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    I suspected the rectified voltage was quite high (I didn't take into account the line voltage consideration).

    Leave it to Tom to find the simplest/bestest answer. :D
  5. W9GB

    W9GB Ham Member QRZ Page

    They are still a good source for some of my restoration parts, like the Cushcraft "R' series matching box :)

    The 24 Volt lamps are also readily found in military / avionics industry in the T1-3/4 Flange base.

    Alpha 76A amplifiers use 24 V Flange lamps for the meters :)

  6. W8JI

    W8JI Ham Member QRZ Page

    I lived through the surplus parts thing when I tried to straighten the mess out Prime Instruments inherited from all the surplus and incorrectly spec'ed parts. :) Been there, done that.
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