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Disconnecting HV without disconnecting the screen

Discussion in 'General CB Services Discussion' started by 357, Dec 6, 2018.

  1. 357

    357 Walkin' the dog

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    ffc6e4a96d.jpg
     

  2. Shockwave

    Shockwave Sr. Member

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    While I didn't watch the second video, the first one appears that the tube remained in cutoff and he did not apply bias current or RF drive. If a mistake were made here I would expect the Grid and Fault indicators to turn red. It's not uncommon for an amplifier to remove screen voltage as a means of placing the tube into cutoff although I could not see the schematic clear enough to confirm that. It also appears that this amp is well protected against faults such as operation without plate voltage.
     
    #2 Shockwave, Dec 6, 2018
    Last edited: Dec 6, 2018
  3. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    07FF652E-6DD1-48B1-A504-D2B6E427DD07.jpeg
     
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  4. 357

    357 Walkin' the dog

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    both the same video, different times.
    the second time he's tuning the amp for max smoke with awwwwwdio oooooooooooohhh check check.
    ffs it has a tuning indicator on it to tune with a rtty carrier.
    total ridiculous
     
  5. Shockwave

    Shockwave Sr. Member

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    If you tune with a carrier, that carrier should match the PEP level the amp will run at. Otherwise the output impedance of the amp won't match the load when it's driven at full PEP output. That full carrier condition can put the amp under a lot of stress especially if it really needed to be tuned. To avoid this some people will use a CW keyer to send a consistent string of dots or dashes and tune to a PEP meter to reduce the duty cycle when tuning. Another way to do that is to put a constant tone in the mic since every half cycle of RF will return the carrier close to zero. Yes, I agree prolonging one syllable of the word audio does look ridiculous.
     
  6. 543_Dallas

    543_Dallas Sr. Member

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    I learned this lesson several years ago with a 250b amp. I picked up a couple of spare tubes and thought I knew what I was doing. I wanted to getter them before putting HV to them. I left the anode disconnected and turned the thing on for a day. The amp in the video is much better designed than that Johnboy was because I killed a tube.
     
  7. nomadradio

    nomadradio Analog Retentive

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    A well-designed tetrode amplifier has a "HV-fail" detector circuit. It serves to shut down the keying circuits if the HV is not applied to the tube's plate circuit.

    73
     

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