I wish I knew…

Wish you knew how to do something?

Wish you know how something worked?

Post it in the comments below, maybe someone who has the knowledge will be able to help, or even do a workshop.

10 thoughts on “I wish I knew…”

    1. Hey Thomi, I use this page from Paul Ruby Amplifiers as the gospel when finishing off valve amps: http://paulrubyamps.com/info.html#FirstPowerUp
      A bleeder resistor for the HV caps is a must, I cut an alligator clip cable in half and soldered the resistor in between the two ends, wrapped up in heatshrink.
      In the absence of a convenient mains switch I keep the power cable plugged into an extension as far away as possible so I’m nowhere near the amp when plugging it in/out.
      If you’re poking around with a multimeter lead, or anything along those lines, always keep one hand well out of the way. Many people suggest behind the back. If one hand is grounded at the chassis when the other gets a zap the charge can pass through the heart which is your best chance of death by electrocution.

    2. I used batteries for the initial testing for mine (an AX-84 SEL). 4x AA batteries in series for the heater supply, and 2x 9-volt batteries in series for an 18 V B+ supply. I had to turn the volume controls up to full, but it produced enough sound for a basic sanity check of the audio circuits.

      For mains-powered testing, a light bulb (say 100 W) in series with the mains supply is often recommended to limit the current (and light up as an indicator) if there is a fault.

      Having someone who knows CPR on hand when working on them is also good!

      1. Never tried it myself, but I believe an isolation transformer is a good idea.

        I theory goes like:

        In a normal 240v supply, neutral is tied to ground, so if you touch the active, you get a 240v jolt (bad!)

        With an isolating transformer, both active and neutral are free to float, so if you touch the active, it tends to float to the same potential as your body (~0v), and neutral instead goes to -240v.

  1. I wish I knew more about antenna design: basic types, pros and cons of different designs, , tips for building, transmitting vs. receiving, optimising for particular frequencies or applications.

  2. Hi. I have a problem with the Lifepo4 battery and charger for my electric bike. I think the charger is under charging, but I’m not sure how to confirm this and fix the charger if required. I have built the battery pack myself, but have reached the limits of my knowledge. Please help!

  3. Hello to Everyone at DSpace,

    Instructables.com is sponsoring monthly build nights at makerspaces and hackerspaces around the world. We are partnering with Sugru for our July build night and would love your space to participate!

    The way it works: we send you several packages of Sugru for a build night and your space posts Instructables from the event.

    You can see details about the build night here.


    If you are interested in participating you can find the signup form at the end of the forum.

    Please let me know if you have any questions.


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