6 - Testing the power supply
barry (Administrator) 12-30-2013 at 03:13 PM.
Post: #1
With the entire power supply now built, we can test it before continuing. The idea is that testing this part of the circuit now means that we'll have less head-scratching if we need to fix a problem later. First, print this voltage chart so that you can record all of the important figures for later reference (or troubleshooting).

[Image: n5xps15.jpg]


Then properly clear your workbench of any compontent lead offcuts, loose wires, wire 'whiskers', etc. Double check - even the smallest could create a short circuit. Then tuck the output transformer's loose wires well out of the way, so they cannot flop around anywhere near the power supply. Get your DMM ready and set to read high AC voltages.

Connect an IEC mains lead to the amplifier and the wall socket. If the wall socket has a switch, switch it on. Use the DMM to carefully confirm that you have your mains voltage at the Live and Neutral lugs of the IEC socket. Record this figure in the first column in the voltage chart.

Now turn the amplifier on. The neon should glow.
- - Quote -
barry (Administrator) 12-30-2013 at 03:18 PM.
Post: #2
[Image: n5xps16.jpg]

Initial AC and DC voltage tests
Use your DMM to measure the AC voltage between points A and B in the above diagram. You should get approximately 430V. Record this figure and the rest in the rest of the figures in the voltage chart.

Now check the AC voltage between points C and D. You should get a reading of about 6.5-7V.

Select the high DC voltage range on your DMM and check the voltage between points E and F. The expected reading is 290V or so.

Turn the Power level control all the way up. Check the DC voltage between E and G for a reading of about 285-290V.

Now dial the Power control down to about midway. The E-G reading should be about 180V. It may take a few seconds to get there.

Dial the Power control to minimum and the E-G reading should fall to around 25V

Stop the project and contact Amp Maker if you get any odd readings.

TIP: Almost all DMMs have switchable ranges to help you get accurate measurements. When measuring smaller voltages, switch to one of the lower voltage ranges. For example, if you measure the heater supply using a 500V range, you will most likely see a figure of '7', but if you switch to the 20V range you would see '6.85', for instance.
- - Quote -
barry (Administrator) 12-30-2013 at 03:24 PM.
Post: #3
Switch off checks
Keep your DMM to hand and switch the amplifier off and disconnect the mains lead from your mains supply. This is a VERY important step - it's easy to forget that when the amplifier is switched off, there's still a potentially lethal voltage at the IEC socket and On/Off switch. As a quick visual check, I pull the amplifier cable from the mains socket to be sure that this voltage is disconnected.

[Image: n5xps17.jpg]

Now recheck all of the DC voltages that you just measured. They should all fall towards zero. Keep checking until they read less than 10V. If it takes longer than 60 seconds, there's a problem - contact Amp Maker.

NOTE: This step is important because it reminds you that the large blue-black capacitors, known as filter caps or sometimes reservoir caps, store a large amount of electrical energy, even after an amp is switched off. The N5X has two bleed resistors - R22 and R26 - that allow this charge to drain away safely and quickly.
- - Quote -
barry (Administrator) 12-30-2013 at 09:18 PM.
Post: #4
Add the heater supply
With the amp switched off, disconnected from the mains and the capacitors safely discharged to under 10V, you can add the heater supply. This runs from the tagstrip to the V3 valve socket, then to V2 and then to V1 - in three long square-ish loops.

For the first section, use two pairs of green wires, with one soldered to each of the outer tags of the tagstrip. Twist the wires together, and run them to the back edge of the chassis, then along the chassis edge and then inwards to the V3 valve socket position. The basic principle here is that we want to keep this wire - which carries AC with a 50 or 60Hz hum - well away from the amplifier's signal path to reduce the noise levels in the amplifier.

Solder the green wires, one to pin 2 and one to pin 7. Now take two more green wires and make a similar loop to connect these two pins to pins 4 and 5 of V2. Here's an annotated diagram to show how the valve pins are numbered.

[Image: n5xps18.jpg]

Finally, make a similar loop to the V1 valve socket and this time connect one green wire to pin 9 and the other green wire to pins pin 4 and 5. When completed, the heater supply will look like this.

[Image: n5xps19.jpg]
- - Quote -
barry (Administrator) 12-30-2013 at 09:24 PM.
Post: #5
Testing the heater supply
Clear your workbench again and get your DMM ready. Plug an ECC83 valve into the V1 valve socket. Then, depending on the power valve you want to use, either:
1) plug an EL84 into V2, or
2) plug a 6V6/6L6/EL34 into V3

[Note: you cannot use the amplifier with all three valves installed at the same time]

Now attach the mains IEC cable and switch the amplifier on. Within a few seconds you should see your valves each glow as they warm up. In a bright room it can be hard to see - there's just a dull orange glow within the electrodes of the valve.

With the amp still powered up, carefully check the AC voltage between pins 4 and 9 of V1. Depending on the valves you are using, you should have a figure of about 6.1-6.5V.

Now unplug the amplifier from the mains. Remove the valves from the sockets and put them safely on one side while you complete the rest of the amp build.

[Image: n5xps17.jpg]
- - Quote -
barry (Administrator) 01-20-2014 at 04:57 AM.
Post: #6
Direct links to reference diagrams
This guide is written in several sections, ranging from a basic description of the N5X to very detailed instructions on how to build each and every part of the amplifier. I recommend following it step-by-step and paying attention to the tips and suggestions.

However, if you're an experienced amp builder, you may just want to dive into the build and do it your own way. To make that easier - and for easy reference for all builders - this, the last entry on each page, lists the important reference diagrams:

* Schematic
* Power supply board
* Main board
* Finished layout
- - Quote -
barry (Administrator) 01-20-2014 at 06:11 AM.
Post: #7
.
- - Quote -
Post Reply