Protect that rig!

I would suggest that the first thing one does after mounting potentiometers, variable, socket etc on the case to house that new rig, is to add some reverse polarity protection. Yes, I know, it will not happen to you; you will never get the connections to the PSU or battery round the wrong way, will you? YOU WILL - I speak from experience!

I remember, some years ago when I had been using my HW7 for a while, when I had a brain storm and tidied the shack up (Oh, the shame of it ...). Guess what I did? I took everything out, had a clean up and put it all back. Fine. But I put the battery for the rig back where it lived THE WRONG WAY ROUND. So, when I next came into the shack, I plugged the rig back in as usual and ... silence. Funny, I thought, it usually fires up straight away. It did fire up - with smoke! A little pall of smoke was drifting from my HW7. This isn't what it does, thought I (quick as a flash), and turned it off. Yes, you guessed it, I had the power connection round the wrong way. If only I (or Heathkit) had thought to fit some protection, my rig would be emitting RF, rather than heat.

So, the moral of that story is FIT SOME PROTECTION! Below are some circuits commonly used to prevent damage caused by reverse polarity.

The first circuit, A, will cause a slight voltage drop especially if used to protect a circuit with higher current consumption. I use B in most of my rigs and C is more refined in that the relay will only work when the polarity is right. Because a relay is empolyed in C, there is however a little more current used.

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