• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Breadboard help

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I have built a few chassis projects but now I want to experiment some before my next project. I have seen numerous pictures on the site of various breadboard setups, and have a few questions.

I will be using a 2 amp fused Variac for the main power to the breadboard. I want this board to be as safe as reasonable given the fact it will have many exposed wires.

Should I still have an inline fuse of some sort coming in to the power supply?
Should I still use earth ground, even though there is no chassis to ground it to? Does an isolation transformer make it safer? Any other suggestions to make the breadboard safer would be appreciated.


Disabled Account
Joined 2010

You have to remember that breadboard projects are no different from a standard build. The fact that it is a bread board project means your safety should be as good or better.
Don't forget discharge resistors across HT caps in power supply.
Test before you touch!
You "must" use an isolation Tx. If you don't your fault current will be higher.
All circuits should have their own fuse, If you get a short it will limit damage done "not prevent it".
Gnds should be at Earth potential " connected to earth".
If you get a gnd fault it will rise to fault potential "Above Gnd" if you then touch gnd you will get a shock!

Any tracks on the bread board should be able to with stand currents used if it is large then "Tin " the track with solder!

For testing an in line earth leakage CB is an extra safety measure!

Don't get over confident "just because it's a bread board project" if it has HT it has potential to kill!

Be safe and have fun!

M. Gregg
Disabled Account
Joined 2010
Just for interest.

In the "early days" of tube radios it was common practice to have a 2 wire system with the chassis connected to Neutral "return" and live straight to a rectifier and circuit. The problem with no Tx between you and supply means that if you contact the live supply when touching the Gnd (" at Neutral / return" ) potential you become the circuit between the two! Or the live may be connected to gnd by mistake.

A power Tx creates a break between the mains and your circuit "you can then make a Gnd on the supply side of the circuit.

Hope this is of help.

M. Gregg
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