I have been looking for a simple, cheap and SMALL amplifier that I could use with my eMac or iPod and still maintain some degree of audiophile credability and along comes this little beauty - inspired by my Italian friend Vincenzo in Sicily.
The Piccolo will produce 2w approx. in triode mode or can be switched to ultralinear mode for 4w. The application of NFB is also optional, but in this case I chose not to use NFB. This is a real little beauty, both is appearance and in sound ... cute, is the word that comes to mind and has a true taste of the triode sound in a very compact 150mm x 300mm chassis and has no right to sound as good as it does!
Released in October 1961, one of the last new general valves, the ECL86 was designed for use in stereophonic amplifiers. Allowing the signals from crystal and ceramic pick-ups to be amplified to speaker-driving level with the minimum of components.
This Mullard advert from November 1961 announces this valve, alongside the AF118 transistor. This period is notable as the time of rapid migration from valve to transistor radios. Valves were beginning to be relegated to high-power and TV use even by 1961.
The new Mullard triode pentode - the ECL86 - is designed specifically for audio applications and is particularly suitable for stereophonic amplifiers. The sensitivity of the valve is such that the output derived from low-sensitivity crystal and ceramic pick-ups is adequate to produce a useful output of 3W from the valve in a atypical single-valve circuit and to allow the use of negative feedback. Special care has been taken in the design of the ECL86 to keep hum modulation to a minimum, and a hum voltage of 4uV, referred to the triode grid, is attainable.
The PCL86/14GW8 - is electrically identical apart from the different heater voltage of 14,5v with a plate dissipation of 9w. Earlier versions of this valves was the weaker ECL82 and before that, the ECL80. The triode section is identical to half a 12AX7A / ECC83. The pentode section is similar to EL84 but not as strong.The anode load is rated at 5100ohms and 9W. It has a B9A base.
Therefore, you can use PLCL86 valves with the heaters in parallel or you can use ECL86 with the heaters in series. The PCL86 valves are somewhat cheaper than the ECL86 type.
Keeping things simple, I used a kit of parts including valves from Elettronica Novarria this includes the power transformer, both 5k output transformers, valves, noval sockets and all the resistors and caps and diodes.....all for the sum of 92 euro. Novarria was founded in 1968 and is a specialist transformer manufacturer in Milan, Italy and this kit represents unbelievable value, though there are some items that have to be added to it, such a volume pot, connectors and such.
However, since I had on hand a couple of new BlackGate FK caps, I put them to use in this as the cathode by-pass and also broke out and used a 10H choke in the PSU. Resistors are carbon film type, 2w, though 1/2w, as supplied by Novarria, would be sufficient, I like the size of these and also higher wattage means less heat, less internal noise. Groundbuss is 99.99 fine silver of 2mm dia. I have certain beliefs about the groundbuss and if I use silver nowhere else, I will use it on the ground wire. RCA inputs are PHY Silver as are the PHY speaker binding posts, again I just happened to have these on hand - otherwise they would cost more than the amp!
The chassis is hand made from 3mm aluminium for the top and bottom, with the side made from 3mm 40x40mm angle retained with two scerws. The method of finishing is to rub down with 80 grade emery paper, followed by 180, 600 and 1200 grades, wet and dry. This will remove any defects or scratches and polishes up real nice as you can see. A final rub with Solvoautosol metal polish with give that final sheen and protects it too from oxidation. The transformer cover is nothing more than 10mm mdf glued together, chamfered and sprayed with car aerosol and fitted with alumimium sides. The 10mm threaded rod on each corner serves as a method of fixing the top and bottom plates together and with the use of dome nuts, provide the feet. It also allows very easy and quick access to the internals.
The PSU has now been modified slightly from the original with the adddition of 200uf in the second stage of the filter, giving now a total of 300uf instead of the original 100uf. This is a very worthwhile improvement with gains in bass and dynamics - without it, the amp seems a little weak sounding.
Schematic - Wiring - Layout - Parts List
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|You can also see a slide show with more photos here ...|
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