Aston Electronics 5W Valve Amp Kit Build – Start
There is a big effect difference between voltage levels that break through the skin conductivity – which happens to be in the 400 to 500V DC range of our amp circuits! BE CAREFUL! Drain the secondary capacitors when the circuit is off and always check the circuit with a multimeter on both AC and DC sides before touching components or working on it – with the mains UNPLUGGED. If the Mains is plugged in, the plug socket and switch contacts are LIVE still, with the switch in the OFF position.
If you are testing the circuit after a change, make sure all your test leads, probes and croc clips are well insulated from your fingers and chassis contact points (chassis edges can be sharp too). I always connect the croc clips and meter and double check. I then plug in the fused mains side. I use the mains toggle switch to power the secondary with the indicator light connected so I can SEE power also, as well as checking the on/off position of the switch BEFORE I plug in the mains. I switch OFF and unplug the mains, checking the meter voltage or current level has dropped to 0V, (or use a drain lead on the capacitors ASWELL) before I move any croc clips to a new circuit point for another measurement.
For the sake of a few extra seconds, why risk safety by not switching off and draining the circuit?
A 240V AC shock will certainly help you not make that mistake again if you ever forget any of this – if you are lucky enough to not get away with it! My last one left my right arm aching for an hour!
A 500V DC shock may mean you don’t get to worry about any of this ever again…but now you know why.
First – check all components match the list.
Use a multimeter for this as it is easy to misread the resistor value colours if you are not familiar or your eyesight isn’t so great anymore (like mine!). After the Marshall fault of an open circuit resistor, you know they all work, also.
I also purchased a capacitor meter off Ebay – a great help correctly verifying the many similar 0.047uF, 4n7 and 470pF values on this circuit, and ensures, like the resistors, that they all WORK before you solder. For 13 pounds or so, its peace of mind, and could save you a lot of trouble before you start. When you have spent 180 quid plus on a kit why not get all the help you can get – especially if this is your first kit build. I’m VERY sure I’ll get a lot more use out of it in future also, while I’m continuing this hobby of buying and fixing amps etc.
Geoff Pugh sent all the PDF docs for the circuit, the eyelet board layout and a 10 page “Help & Instructions” PDF, giving hints on build order etc.
I have now got to the pre-solder eyelet board component layout stage, and fixed most of the chassis parts in place:
I used solid mains Earth copper links, cut from house wiring cable for the circuit ground links rather than multiple lengths of black link wire, where possible.
The eyelet board layout will be triple checked at LEAST, against the schematic AND circuit layout pages, to be sure they are correct before I go near it with soldering iron – desoldering mistakes is not fun – and it makes a big mess. Best to get it right first time!
If you are interested in making your own amps from the many valve circuits on the Web, here is a page on how to make your own eyelet board:
I bought a set of stake punches from Ebay for 2 quid!
The next step is to print out the layout diagram in colour once I have a new cartridge for my expensive refill Lexmark! Then I can cut the coloured wires to length, tin and solder them to the board where required….
Next Post – Middle bit…soldering…