Maddog's Lamington Jr Amplifier build diary

[JohnH]

Looks great Scott! Im always impressed that people build amps; they kind of terrify me

[moody]

Looks great Scott! Im always impressed that people build amps; they kind of terrify me

There is a reason for that, they are dangerous. The best person to build one is somebody with a healthy respect for that danger.

[JohnH]

There is a reason for that, they are dangerous. The best person to build one is somebody with a healthy respect for that danger.

One hundred percent

[churchie]

Looks great Scott! Im always impressed that people build amps; they kind of terrify me

I'm too scared to change my tubes

[Marcel]

It is always healthy to maintain a solid respect for electrickery and all those lazy electrons that will always take the easiest way to get out of doing real work.

Fear helps in that maintenance of respect. Electrons can act way faster than we can think so you need to be at the top of your game plan if we are to constantly out smart them fast lazy buggers and get them to do the work we want.

By work I mean make our air-conditioner and fridge do its thing, make a light bulb glow so we can see, do whatever it does that makes our smart phones be smart, and gather in numbers to make our wonderful axe builds pump that 4x12 cab.... And that's the problem, when they gather in numbers that is often expressed in Volts, and they gather in huge numbers inside a tube amp, and every single electron is constantly looking for an easy way to get out of doing the work we want....and we can't let them take the easy way out by jumping through us to ground....

The simplest way for us to ensure they all do the work we want is not to touch where they are... Don't touch the wires !!... Only touch the insulating parts, the plastic or the glass or the wood... Never touch the wires or any metal bits attached to the wires be they Copper or anything else!!...

Of course there are metal parts we do need to touch but they should all be earthed. It's the reason for the earth wire to the bridge, and why a power cable has an Earth pin that is connected to the metal chassis of our amps, and why there are Earth pins on power outlets and why Electricians put that Green/Yellow wire on every bit of copper pipe in a house to make them electrically safe. (Note - Green/Yellow stripe wire is an international standard for all and only Earth/ground connections, and the reason those colours are used is because fewest people in the world are colour blind to that combination)

Keep that respect for an (every) electrons laziness and there should be no reason for them to take a possibly lethal short cut through you...

[DrNomis_44]

Well said Marcel, one thing I always made sure I did when doing any 240V AC wiring in some of the things I built that were powered from 240V AC, was that I always made sure that the fuse was placed in the Active part of the 240V AC mains wiring to the power transformer after the power switch, the reason for that is if the 240V AC primary winding of the power transformer develops an internal short-circuit, then the fuse will blow and instantly (well almost instantly) cut off the power, that's assuming that the fuse is appropriately rated of course, doing this also ensures that the metal chassis will not become live at 240V AC, a very dangerous situation.


I'm definitely going to have to invest in a device called a Megger soon, so I can do insulation testing.

[chrissyinbkk]

Oh thats just taken me back to the 70's... a megger.... and that was the last time i used one...

[Simon Barden]

They are still widely used for electrical insulation testing. Megger is a brand name, they now do a lot of test products. https://uk.megger.com/products/insulation-testing
The only problem with them is the relatively high voltages they use (500-1000V) can destroy products which use ELV circuits that aren't meant to be insulation tested.

[Marcel]

Back in high school we had a few wind up Megger's of different sizes....a very basic instrument that had a crank handle to make it work which often got used by the nasty kids to zap unsuspecting victims...

I have two insulation testers both made by Kyoritsu. Both need to be loaded with 8 AA cells to work (and so have nil crank handle like the old Megger units) and thankfully the batteries last a reasonable time.The newer one is digital and does timing tests on RCD circuit breakers as well as insulation tests at 250V, 500V and 1kV. The older analogue meter one I've had for near 30 years does the same HV tests as well as a highly accurate ohm measurement...

On the HV test settings they both do produce the identified voltage but due to internal high resistance of the meter itself there is very little current. Even when the test probes are shorted together there is only a few micro Amps flowing through the wires, which is enough to give you a small shock and destroy most transistors but is typically not enough to kill a person.

At a price point, for the cost of the digital meter I could have bought two fully upgraded top line PBG kits, and 30 years ago the analogue meter cost half that or what amounted to a weeks wages back then.

[wikid of Oz]

Back in high school we had a few wind up Megger's of different sizes....a very basic instrument that had a crank handle to make it work which often got used by the nasty kids to zap unsuspecting victims....

In the first two years of my apprenticeship everyone used to use a megger to charge capacitors and throw at each other to catch. The the great fun nazis from safety and HR put a very quick stop to it. Used to hurt like buggery but was funny as