11 - Final testing
barry (Administrator) 12-31-2013 at 06:01 AM.
Post: #1
With the chassis ground continuity and Earth continuity tests passed, you can move on to the final part of testing. These are the most safety critical tests, and you should make sure that you won't be interrupted or distracted by children/pets/TV/etc. Remove jewellery/etc that might dangle into the amplifier chassis.

First, unplug the guitar lead from the amp’s Input socket. Then plug a suitable speaker into one of the speaker outputs. Make sure there are NO VALVES installed for the moment.

Then plug the IEC mains cable into wall socket and switch the amplifier on, keeping your fingers, multimeter probes, etc outside the chassis. The neon light should start to glow and you may hear a low-level acoustic hum from the power transformer mounted on the chassis. This is normal. You may also hear a very low-level hum from your speaker – this is electro-magnetically coupled hum directly between the two transformers and is also normal. If you hear a loud hum or buzz, or if the fuse blows, switch off immediately and contact Amp Maker.

Print off this voltage chart, ready to write down the results of your tests.

[Image: n5xft01.jpg]

In the bottom right corner of each cell in the table, there's a typical figure in italics. Write the actual figures you measure in the table.
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barry (Administrator) 12-31-2013 at 06:02 AM.
Post: #2
Testing without valves
We now move on to check the same voltages we checked after building the power supply. Write your figures down in the first column of the above chart.

First, use your DMM to measure the AC voltage at the IEC socket.

Then do the same between points A and B in the diagram below. You should get approximately 430V.

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.

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

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

If the readings are all correct, switch off the amplifier and unplug the mains cable before moving on to the next step. Contact Amp Maker if you get any odd readings.
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barry (Administrator) 12-31-2013 at 06:09 AM.
Post: #3
Testing with valves
Insert the valves: an ECC83 into V1 and either an EL84 into V2 or a 6V6/ 6L6/EL34 into V3. Set all of the amplifier’s pots to minimum, except the Power level control - set that to maximum. Put the Boost switch in the centre and the Bypass switch up. Make sure there’s no guitar plugged into the Input, but do plug a suitable speaker into into one of the outputs. Now plug the IEC cable into the mains socket and switch on.

Start by repeating the measurements you did with no valves installed, and record the numbers in the correct column of the chart (depends on the valves you are using):

1) Mains AC voltage at the IEC mains socket (may have changed a little since the first test, depending of time of day, etc)

2) AC voltage between test points A to B may read slightly lower now that the transformer has a load.

3) The heater supply at C-D may also be a fraction lower – typically 6-6.5V

4) The DC voltage between test points E-F will also be lower, around 250-260V

5) Measure the E-G voltage, typically around 250V.

6) Turn the Power level to minimum and remeasure E-G, typically ??V.
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barry (Administrator) 12-31-2013 at 06:26 AM.
Post: #4
Final measurements
That last set of measurements lets us know that the power supply board works properly under the load of the circuit. The remaining measurements let us check the DC state of the rest of the N5X amplifier circuit at idle. From this we do a few simple calculations to check everything's within spec and then we're ready to play.

[Image: n5xft02.jpg]

So use the annotations on the above diagram and measure and record the rest of the voltages in the same column of your chart.
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barry (Administrator) 12-31-2013 at 07:02 AM.
Post: #5
Checking dissipation - EL84
If your readings are all close to the 'typical' values in the voltage chart, then we just need to do a few calculations to confirm that the amplifier's biased right and we're not burning up the valves prematurely.

This section covers an EL84-based amplifier. Skip to the next section if you are using a 6V6/6L6/EL34.

1 - EL84 cathode current: Divide the cathode voltage (H-N) by the value of R16 (150Ω). A typical result is around 43mA. Contact Amp Maker if it's more than 50mA.

_________mA

2 - EL84 screen current: Divide the K-L figure by the value of R18 (2.2k). A typical result is 4mA. Get in touch if it's more than 6mA.

_________mA

3 - EL84 plate current: Subtract the screen current (2, above) from the cathode current (1, above) to get the valve's plate current. A typical result is 36-40mA. Contact Amp Maker if your result is more than 45mA.

_________mA

4 - EL84 plate dissipation: Multiply the N-M figure by the EL84 plate current you've just calculated (3, above).

_________W

For example, 225V * 0.039A = 8.78 Watts dissipated by the EL84's plate. This is a typical result. A value under 8W or over 10W needs some consideration; contact Amp Maker.
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barry (Administrator) 12-31-2013 at 07:12 AM.
Post: #6
Checking dissipation - Octal valves
This section covers an amplifier with a 6V6/6L6/EL34 power valve. Use the section above if you are using an EL84.

1 - Octal cathode current: Divide the cathode voltage (H-J) by the value of R17 (470Ω). A typical result is around 30-40mA, depending on the valve you are using. Contact Amp Maker if it's more than 50mA.

_________mA

2 - Octal screen current: Divide the K-L figure by the value of R18 (2.2k). A typical result is 2-4mA. Get in touch if it's more than 6mA.

_________mA

3 - Octal plate current: Subtract the screen current (2, above) from the cathode current (1, above) to get the valve's plate current. A typical result is 36-40mA. Contact Amp Maker if your result is more than 45mA.

_________mA

4 - Octal plate dissipation: Multiply the J-M figure by the octal plate current you've just calculated (3, above). For example, 235V * 0.037A = 8.7 Watts dissipated by the octal valve's plate.

_________W

For 6V6 valves, any value under 12W is fine. For 6L6/EL34 a value up to 15W is fine. (See the Tone Tweaking section for more information on biasing octal valves.)
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barry (Administrator) 01-20-2014 at 04:47 AM.
Post: #7
[Image: n5xft03.jpg]

Plug in and play!
With all of the tests safely passed, you're now ready to plug a guitar in and play. Start at low to medium levels of the Gain and Master controls and test each of the other controls in turn. Each should operate smoothly.

Check the extra gain provided by the Boost and Bypass switches. Remember that the Treble, Middle and Bass controls won't work when the bypass switch is down.

The Power level control is a linear pot, which means that the audible effect you hear from turning it down is more pronounced at the bottom end of the dial than it is at the top. This is normal.
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