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Author Topic: Safety/how do i stay alive during amp tube r/r  (Read 8603 times)
WA9SVD
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Posts: 2201




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« Reply #15 on: October 28, 2007, 03:48:19 PM »

You definitely need a shorting stick, but it should have a (relatively) high resistance included, otherwise, shorting the HV before the bleeder has started to work can cause a large surge current and possible destroy some components.  Apply the shorting stick, then leave it in place and brew a cup of coffee, or read the front section of the newspaper.  Come back several minutes later. and with the shorting stick still in place, apply a jumper wire (with alligator clips on each end) between the HV and ground.
    Only then can you remove the shorting stick.
    Next, use a volt meter on the highest voltage scale to probe and make sure you didn't forget any areas than need to be discharged.  Use additional jumpers to insure all voltages are reduced to zero. THEN do your repairs.
    While you have the amp shut down, subdued, and powerless (pun unintended?) to hurt you, take time to inspect (and even check) all the parts to look for unsuspected damage or deterioration.  Leaking capacitors, charred resistors will need to be replaced, even if they haven't completely failed.

    THEN (and this is VERY IMPORTANT) remove ALL of the shorting jumpers.  (The power supply will appreciate it when you turn things back on.

    The best thing is to get an experienced Amateur to guide you through the process, at least the first time.
    While "sending the amp back to the manufacturer" is a possibility, it's (IMHO) poor advice.  We ALL had to learn, including learning about working with HV in a safe and sane manner.  Follow safety suggestions and procedures, and YOU will become one of the experienced Amateurs in the future.  You won't learn anything by shipping the amp off somewhere to get it repaired or retubed.

    Be careful, and good luck.
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W6IEZKEN
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Posts: 29




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« Reply #16 on: November 13, 2007, 05:56:33 PM »

     Certainly HV is the main concern but don't forget sbout other things that can hurt you like 110VAC relays and try not to break anything while working on the amp.Using screwdrivers to arc to ground can damage components like transformers,use a shorting stick to bleed the charge of slowly instead  of becoming an arc welder.Touching hot tubes or components can cause you to touch HV.Do not work when tired,someone else should know how to turn off all power.Arcing,parasitics or burning components can cause cuts, burns.Do not work with your bare hands;always wear rubber gloves underneath work gloves.The work gloves protect you from heat and sharp edges that would cut you or the rubber gloves; the rubber work gloves(Not latex) protect you from HV.Work with a rubber mat under you and a dry surface.Goggles will protect you from exploding components (capacitors,transformers) when you have to test an amp under operating conditions that may have defects.OSHA even has more requirements like rubber aprons and this may sound like overkill but all of these practices are followed when working on high power broadcast transmitters.The only difference is a 1KW will electrocute you, a 50KW will vaporize you! This is not meant to scare you but to keep you from becoming an SK.     Think safe.
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KA5ROW
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Posts: 500


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« Reply #17 on: December 16, 2007, 05:37:19 PM »

We all make mistakes.  Don't let your name and Call in up in QST " Silent Key"
people who know every thing there is to know about amplifiers. Make  mistakes too.
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