Have your say & ask the experts

I love this thread. I'd love to have a go at something like this.

lordmortlock:

I love this thread. I'd love to have a go at something like this.

 

Totally agree, I'd love to try my hand at this sort of thing - although I'd need a fire extinguisher handy for the big switch on! 

Those cases are absolutely stunning too! If I could get something like those, in plain 'ol aluminum, I could see a very sexy future built...

Martyp:

lordmortlock:

I love this thread. I'd love to have a go at something like this.

 

Totally agree, I'd love to try my hand at this sort of thing - although I'd need a fire extinguisher handy for the big switch on! 

Those cases are absolutely stunning too! If I could get something like those, in plain 'ol aluminum, I could see a very sexy future built...

Well, you're in for a treat. Today I have been buying metal....we are moving into light engineering!

The PCBs and transformer all need to be bolted down and what I want to avoid is drilling loads of holes in the bottom panel of the case. All I want is four holes to mount the feet and maybe one in the middle for the star ground mounting. So, what I'm going to do is insert a plate into the bottom of the case, raised up on metal bar feet.

This'll mean that I'll be able to drill as many holes as I like in the plate and they won't be visible from underneath the case. It'll also allow me to reuse the case and make construction easier, cos I can get anything fixed down and tested outside of the case (reduces the risk of scratches if nothing else).

So, I found this place online....Ringwood Precision Engineering....which is just up the road from me. It a proper engineering workshop. Loads of machinery and stock packed into a fairly small area. It was great visit actually, looking through the stock; great big lumps of aluminium, stainless steel and copper plate.

I know. I'm sad.

Anyway, I finally went for two sheets of 2mm aluminium sheet measuring 290mm by 210mm. I also got a 820mm length of 10mm square bar. All in, £17. Now I need to buy some additional tools i.e some thread taps to allow me to fabricate my tray. Can't wait.

Crikey, you're turning into Ken Ishiwata.

Who? [googly]. Hmmm. Thanks for the compliment but I suspect you're gonna be disappointed when you see the smallish square of aluminium sheet with little blocks of bar screwed onto the bottom.

I've noticed that a number of experienced DIYers recommend building a tool for testing power supplies. This, apparently, gives you an early indication if you've done something silly. The tool is a box with a light bulb on top and a couple of switches. I'm not altogether sure I understand how it works, but it is simple enough to build.

The PSU test tool I'm going to build is this one.


Nuukspot's Bulb Tester

That is just an excuse to keep building stuff. Next it will be a test tool to test the test tool! The site you linked to is scary, way too much red writing warning of deaths and explosions if you get it wrong.

idc:

That is just an excuse to keep building stuff. Next it will be a test tool to test the test tool!

Yes, I know. And I keep finding reasons to buy stuff too.

idc:

The site you linked to is scary, way too much red writing warning of deaths and explosions if you get it wrong.

The only bit that dodgy is the wire going from the IEC socket to the transformer. This is 240v. However, I've got a strategy to sort this.

If you're really nervous, you could skip the PSU and use a wallwart. I've had a look at these but they get a bit pricy when you need 18-30v at 6A or above. But you could use a much smaller case (big saving). Not quite sure how you'd go about grounding though.....

@pjpro, lovely detailed commentary as ever, all being filled away in my head for sometime next year after we move house

The amp looks great so far thanks 

Thanks zzgavin.

OK. So I've got my bits for the bulb tester (see below).


Bulb Tester bits

I'm going to use a plastic box, so I can forget the issues of grounding. What I hadn't considered was that I need components which did not have any metal parts which pierce the case. So, the IEC sockets and the lamp holder need to be changed. I'll go for clip-in versions of the IEC sockets and the sort of lamp holder than usually hangs by a wire from the ceiling.

The illumunated switches looked they were going to be a problem too (no markings) but I've had a clarification from someone about wiring these in.

As usual, I'll provide a narrative and pictures to cover construction as I go.

Back to the main build.....

I needed to fit the feet and create the inner tray. After some careful marking out, I drilled four 5.5mm holes through the bottom of one of the cases. These were deburred using a 12mm drill bit.


Drilling holes...


Four new de-burred holes.

I then bolted the two bottom trays together, using holes which were already present in trays, to allow the first tray to be used as a template for the second. I used a similar technique for the inner trays except that clamps were used.


Using the first tray as a template for the second.

Now I need to prepare my little blocks of aluminium. The idea was that the feet would bolt into the bottom of the block, leaving enough space for the inner tray to be bolted on from the top....like a long nut. So, the first step was to drill the bar.

The thread projecting from the feet is 5mm wide. So, allowing for the thread itself, I needed to drill a 4.2mm hole.


More drilling...

With the holes drilled, it was now necessary to create the thread. I used a tapered tap to start the thread off and finished the job with a plug or bottom tap.


Creating the thread.

All that remained to do for the blocks was to cut them from the bar and remove any burrs.


Spacer blocks coming off the bar.

Here's one of the trays with the feet fitted and the inner shelf in place. The inner shelf still has its protecive film attached. This will allow me to attach the PCBs, transformer, heatsink, etc, to the inner tray without having to put loads of holes in the bottom tray.


Bottom tray with feet and inner tray.

I mentioned the Bulb Tester Tool earlier in this thread. Well, I've consulted the experts to understand how it works and build my own, based on the Decimal Dungeon version.

What does it do and how does it work?

Provided by pacificblue

Light bulbs are temperature-dependant resistors. The higher the temperature, the higher the resistance (PTC - positive temperature coefficient). That is, why they usually blow the moment, they are switched on. Their resistance is low then.

Now connect an amplifier in series and switch it on. The inrush current is high and will probably make the bulb light up for a short moment. If the amplifier is okay, there will not be much current draw after that -> low current through the lamp -> no heat, no light -> low resistance -> no voltage drop across the lamp -> full voltage at the amplifier. If the amplifier has a fault, it will draw a big current -> filament heats up, lights up -> resistance goes high -> high voltage drop across the lamp -> reduced voltage at the amplifier. There is your cheap and easy current limiter.

Provided by Redshift187

If the bulb is wired in series with the Live as it should be, all current must pass through the bulb. At low current, the filament will not heat much, and resistance will be low. As current rises, the filament heats, and resistance rises. It acts as both a current limiter and a warning device (if the bulb is full on, there may be a short). This protects your equipment (and you!) while allowing you to check voltages.

Hopefully, given the above statements, you'll understand what the thing does.

My summary would be that the tool is a current limiter which provides an indication of sustained high current demand over and above that expected for the device under test. This sustained demand indicates a problem with the device.

I'll provide details on the variants, from the most basic to the delux version I've made, in subsequent posts.

In its most basic form the bulb tester is no more than a lamp holder which is placed in series on the live wire.

A more fancy version places a switch before the bulb to allow the current to be switched off rather than having to reach down to the wall socket to switch off the power. Handy if you need to act quickly!

The next variant places a switch across the bulb allowing the bulb to be shorted out. This allows the bulb to be taken out of the equation once the test has shown the device to be OK, without having to disconnect everything to plug the device directly into the mains. The illustration for this approach, as recommend by Decibel Dungeon, is posted above.

Finally, a further enchancement is to replace the push to make switches recommended by Decibel Dungeon with illuminated switches which provide an instance visual indication on the configuration of the tool.

I went for the latter version with illuminated switches. I had to didn't I.

The BoM for the delux lamp holder is.....

ABS Box BZ75S
16A Rocker Switch Red GU55K
16A Rocker Switch Green GU56L
Euro Chassis Plug HL15R
Euro Chassis Socket FT63T
Insulated Crimps Blue JH82D
5A Terminal Blocks LR97R
Lampholder FQ02C

You'll also need some 5A twin and earth (to use for your hookup wire), earthing sleeve, a kettle lead and a lead with a Euro Line Plug at one end and a Euro Line Socket at the other.

My old PC had a lead which allowed the monitor to be powered from the PC. This is what you need for the last lead specified above. If you haven't got one, use a kettle lead and just change the wall socket plug for one of these.

Please note that the case I'm using is plastic...therefore I don't have to worried about earthing the case. One important consideration is that no metal parts must pierce the case. The plug and sockets which I use are designed to be screw/bolt attached. To get around this I have glued the plug and socket onto the case. Alternatively, one could use plastic bolts.

Just so we are clear, here's a picture of what we are trying to build. The brown wire is live, blue is neutral and green is earth.


Bulb Tester connections.

OK, the first step is to drill a hole in the bottom of the case. I'm using a pillar drill and forstner bit here....but you could use a hand drill. This hole allows the lamp holder to be attached to the case.


Drilling a hole for the lamp holder.


Attaching the lamp holder.

Next to go in are the switches. These clip in place, so you need to ensure that the holes that you make are the right size.


Measuring the width of the hole required for the switches.

Mark out the holds on the case and then drill round the edge of hole, push/cut out the waste bit and file the hole square. Do the same for the other hole and then fit the switches.


Drill around the hole.


One hole complete.


Switches fitted.

Do the same for the IEC sockets and glue in place. I used clamps hold everything together for an hour or so, to ensure a good bond.

The next thing to do is to start hooking up the components. I've used crimps here and a terminal block to make things easier. Also note the slack in the earth (yellow and green). You want this wire to be the last to become disconnected if there's any tugging on the wires. The power will be coming in from the left in the first picture.


Live connections.


Earth and neutral connections.

The only thing that remains is to put on the lid (on the bottom) and the tool is complete. Please note which side the IEC plug and socket are on. It's important to get these round the right way.


The power goes in this side from the wall socket.




And comes out of this side and attaches to the device under test.

I haven't tested my bulb tester yet as I can't find my PC to monitor power cable....so I'm probably going to have to make my own.

I'll demonstrate how the use the tool when testing my power amps.