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Some recommendations received in the process of learning materials.
Never install electrolytes "all the way" between them and the board should be a small gap. The fact that the leg is heated during soldering and is extended and shortened by cooling down, and when tight fit may simply fall off from the electrode. Given that the tube amp heating process, cooling occurs regularly, at this point it is worth paying attention to. Chassis output and power transformers with positioned perpendicularly to reduce mutual interference. Input audio connectors isolated from the chassis in order to exclude the possibility of "ground loops" in the signal lines. If the shield wires - the screen is grounded on one side only. To order accessories with a margin in order to avoid delays in the logistics and save on shipping. And most importantly - be careful with buying a set for ebay (more on that later). of the problems encountered by, turned out to be the choice of the transformers (power and output) - is quite difficult to buy a transformer with the correct voltage, if the 110-volt version and usually is available at US retailers, the transformer 220V to be ordered from the manufacturer and wait 45-60 days. In addition, they are quite heavy and shipping costs from the US nearly doubles the cost of the order. Fortunately, a suitable version (Hammond 374BX) was found in Germany , allowing vital save on shipping and incidentally order choke (inductance) to use power supply output filter. The first mistake - ordering inductance, I picked up the resistance, completely forgetting about the current, to obtain a coil with a current limit rather than the minimum required 100ma 170ma, had Venuto to a simpler and less quality version with RC filter and purchase meets both the wire resistor to change the same resistor the coil, if there is a wish, at any time. With the transformer output was easier adequate delivery times were only Transcendar, all parameters approached model TT-119 .
Finally, the time has come when all the parts are obtained, denoting the free time and nothing hurt to see how all this will work. In violation of safety rules, all connections have been made directly on the table in front of the monitor.
On the role of the source was invited to an old LG-P500, as speakers - speakers from the music center, it took a certain amount of red tape and a little courage. Taadaaaam - inclusion took place, nothing exploded, lamps lit up beautiful orange ... and silence, or rather, if you bring your ear to the column on the background noise could even hear the music, but it was not quite the "warm tube" sound, which I had hoped hear.
The first thing I decided to check - is the output voltage of the rectifier, and immediately was unpleasantly surprised me instead of the expected 375V x √2-27V = 503.33V (secondary voltage multiplied by the square root of minus 2 falling on the lamp) I saw almost 550V output rectifier and accordingly 525V B + (anode voltage). The desire to test electrolytes endurance (they are designed for 500V) absent, had to turn off the power. Check the line voltage once again I was surprised - it was more than 240V (further questioning neighbors confirmed that this is all true). Fortunately, you can rewire transformer and a voltage. The second time on the voltage returned to normal, but the column on prezhdnemu silent, further checks found no anode voltage at the input transistor, which in my opinion, a malfunction of a single semiconductor device - controlled current source IXIS10M45.
Deciding that the problem arose due to overexertion and / or Chinese ebay-seller, ordered a new pair IXIS10M45 from England, it seemed safer and faster. I must say that the inclusion of another completed absolutely similar to the first and second, new parts, though very differently, but refused to work the same way. Here I was beginning to worry, since both channels behave identically, and the anode voltage 12AT7 completely absent. Since this circuit except the actual lamp current controller and a priori running small things nothing else was, suspicion fell on the lamp. Auction on ebay allowed quite inexpensive to buy ECC81 (the European equivalent of the American 12AT7), and along with another batch of IXYS 10M45 (again Chinese seller, took longer to reserve just in case). Third Party 10M45 looked (and calls) in the same way as the second, for the purity of the experiment of replacing the lamp and IXYS, unplug all unnecessary (second stage) and for the fourth time did not find anything at the anode of the first transistor.
Complete failure, mind refused to understand how this could be. Assembled on the breadboard a simple circuit with LED and adjustable current source (used untouched from the third party), powered by a laptop power supply - and it will not work !!!
At this point I began to pursue the idea of universal conspiracy, does not even work that was required to work ... and again, I decided to order the chip problem, only this time through a trusted seller (Digikey). And once again experiencing difficulties, even where they are not supposed to be. The first problem (in Digikey minimum cost of delivery to my area is $ 75, even 5-dollar order). This problem was solved with the help of the American mediator, but the second was revealed after placing an order - in my email I received a letter asking you to confirm that I am not a terrorist fill out the form BIS711 (anyone interested goo.gl/VAkDYB ). I ordered a regular radio address to the US, why do you need to complete this form when purchasing conventional electronic components I still do not understand. Stating your name your name and home address in all fields, namely: I - the end user, I - the official representative of the end user, I - the buyer, I - exporter and pointed out that with all this, I - an individual, send the completed form to Digikey, and the next day I received an order confirmation and traking on the parcel.
Another batch looks different from all previous ones, that inspires otpimizm (picture below)
Checking on the breadboard cheered, happily LED brightness changes depending on the resistance of the resistor control. Five minutes to replace parts on the board ...
... The next switching ON and the speakers sounded music.
As it turned out in the communication process on the relevant forums - fake radio on ebay are becoming a big problem. That's what they write moderators Diyaudio
- Fake parts are a real plague by now. No small chance we all get a share of those when fishing for a quick small purchase.
- I never buy semi-conductors or electrolytic capacitors on eBay for this reason.
- fake parts - problem of our time and the chances of running into them at low urgent purchases are large enough
- So (...) never buy semiconductors or electrolytic capacitors on ebay blockquote>
As a result, I got a working board, regained their self-esteem, disillusioned with Ebay. In haste was manufactured housing was supposed as layout configurations for testing, but suddenly you like.
At present, the amplifier works in conjunction with the Raspberry Pi & Volumio (as a source), the sound is really very nice and really warm (65 ° C +). The plans to refine the body, to overcome a little disturbing hum embed USB DAC (sound card will lamp), it is possible to add a remote control. If there is interest, I will describe the process of construction of the body, as well as talk about the problems identified and ways to overcome them.