10 - Final testing
barry (Administrator) 06-16-2014 at 07:04 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 inputs. 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: p18te03.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) 06-16-2014 at 07:24 AM.
Post: #2
[Image: p18te04.jpg]

Testing without valves
We now move on to check the same test-point 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 290V.

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 400V.

Turn the Power level control all the way up. Check the DC voltage between E and G for a reading of about 395V.

Dial the Power control to minimum and the E-G reading should fall to around 35V

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) 06-16-2014 at 07:29 AM.
Post: #3
Testing with valves
Insert the valves: ECC83s into V1 and V2 and EL84s into V3 and V4. Set all of the amplifier’s pots to minimum, except the Power level control - set that to maximum. Put the Output switch to Mute. 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 right-hand column of the chart:

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 355V

5) Measure the E-G voltage, typically around 350V.

6) Turn the Power level to minimum and remeasure E-G, typically 35V.
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barry (Administrator) 06-16-2014 at 07:31 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: p18te05.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) 06-16-2014 at 07:39 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.

1 - Combined EL84 cathode current: Divide the cathode voltage (H-M) by the value of R22 (150Ω). A typical result is around 75-85mA. Contact Amp Maker if it's more than 90mA.

_________mA
2 - Combined EL84 screen current: Divide the L-K figure by the value of R24 (1k). A typical result is 7-9mA. Get in touch if it's more than 10mA.

_________mA
3 - Average EL84 plate current: Subtract the screen current (2, above) from the cathode current (1, above) to get the power valves' combined plate current. Divide this figure by two to get the average; a typical result is 35-38mA. Contact Amp Maker if your result is more than 45mA.

_________mA
4 - EL84 plate dissipation: Multiply the M-I figure by the EL84 plate current that you've just calculated (3, above). For example, 335V * 0.035A = 11.7 Watts dissipated by the EL84s' plates. This is a typical result. A value under 10W or over 13W needs some consideration; contact Amp Maker.

_________W
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barry (Administrator) 06-16-2014 at 08:04 AM.
Post: #6
Time to plug in!
With the above checks and calculations done and any mistakes rectified, you can finally listen to your amplifier. Start with the Volume and tone controls at about mid-way. Plug in and play your guitar. The guitar tone should give clean to mild crunch tones depending on how hard you hit the strings.

If you get unexpected effects from these knobs, it's possible that you've mis-wired the controls. Go back and check (remembering to unplug the amplifier and discharge the capacitors before going in to work on the circuit).

Now crank the amplifier and check its overdrive tone.

Congratulations! Smile With all of your testing completed, switch off and unplug the amplifier. Check the capacitors have discharged themselves and then build your working chassis into your enclosure (head, combo, etc). If you haven't decided yet, check out the Customer amp gallery for ideas and inspiration.

[Image: p18ak01.jpg]
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barry (Administrator) 06-16-2014 at 08:11 AM.
Post: #7
Direct links to reference diagrams
This guide is written in several sections, ranging from a basic description of the P1800 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 layout
* Main section layout
* Finished layout
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