GOOD
STUFF


HOME

DEDICATION

THE OP'S

WHY HAM RADIO - WHY NOT CB?

YOUR FIRST RIG

HF AMPLIFIER BASICS

GROUNDED GRID BASICS

POWER SUPPLY BASICS

WHAT NOT TO DO AROUND HV!

REFERENCE MATERIAL


What NOT To Do Around High Voltage

Whether you design and build a power supply for your RF Amplifier yourself, or simply stumble onto one on the way to the grocery store, there are a few things about these monsters that are worth knowing about.

First, not only do they use a lethal (the word here is lethal, not legal) voltage to produce the mass amount of DC required to power your amp, but to no one's surprise, the voltage most generate is enough to drop a large horse (maybe even several), dead in its tracks. So, its probably a good thing to keep dogs, cats, goats, horses and small children away from any open portion of the supply, or any terminal that may have voltage present. Not so long ago a fellow emailed me about a mouse that crept in to his supply and came across the terminals of his filter caps - I guess aside from the popping, crackling and sparks, the smell of charred rodent clung to the shack like a sick kitty to a hot brick for a month afterward.

Aside from their awesome power, voltages above 1,500 volts, or so, take on some rather weird twerks. For example, it develops the ability to leap from point to point in a single bound - attempting to use poorly insulated connectors (BNCs work great here) may well result in their permanent (welded) attachment to the chassis (been there - done that). Its amazing ability to span distances also has an interesting effect on volt-ohm-meters not equipped to handle high voltage - kind of neat to watch, really - as the test leads first sag and begin to smoke and the meter's needle spins around in circles, sparks inside light it up like a Christmas tree. Sometimes the show last for only a second or two; sometimes it goes on seemingly forever. After the show's over and it cools down, you can use it as a room deodorizer of sorts, particularly if you're still suffering from the stench of charred rodent - or, better yet, make your friends think you're a super ham - tell them you were holding it when it went off.

When high voltage arcs, it has a dramatic effect on capacitors and resistors that may be in the same circuit. While resistors occasionally burst, they're no match for disc ceramics which often give off a report similar to a Black Cat (what's a Black Cat, you ask? Why, its a firecracker that's sold under the table at fireworks stands every 4th of July!) - imagine a Black Cat exploding right next to those precious 3-500Zs!

When attempting to work on either the power supply or the amplifier that's connected to it, it's often wise to make sure the power is disconnected (unplug it!) and that the capacitors have been drained. Draining charged caps, however, doesn't mean sticking a screw driver between their terminals - to the circuit, that looks like a dead short. Not only can it suck the life out of your diode string, but it can also permanently weld your precious screw driver to the terminals of the filter cap. Instead, use a 1 or 2 meg resistor across the terminals. It will take a little longer, but shouldn't result in the necessity to haul out a hack saw just to remove that screw driver. Do not, however, use your tongue to see if there is any voltage remaining in the caps (like you've done with a 9 volt battery)! To do so, could put an end to your ability to enjoy the delicious taste of those wieners barbecued on your George Forman Grill.

And, speaking of wieners, don't ever try to cook a wiener by inserting a high voltage probe in each end of it - not unless you want to be wiping hot dog chunks off the walls of the shack for a week.

Best 73s - Bob


MORE GOOD
STUFF


SELECTING A TUBE

RF INPUT CIRCUIT

RF TANK CIRCUIT

TRANSFORMER POWER CAPABILITIES

PARTS IS PARTS

ROLLING YOUR OWN - TRANSFORMERS AND CHOKES

POWER SUPPLY PROJECTS

LEGAL LIMIT AMP PROJECT