• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Proyect with PL36 and N2P (Russian ECC83)


2007-10-18 6:40 pm
I present the project that I have finish and it tries to be my goodbye of the world from the electronics after many years working like technician, first in Sony and later in Philips.


To carry out this project left from the base of that I wished a powerful amplifier of valves, of clean and discreet sound, this is that it did not go off key in my hall, easy to use, that my woman can use it without greater problems, different from the others, and, outside mainly only, that the design is done on my own; it is really tried to create something in which to spill all the accumulated experience during every year which I have dedicated myself to the electronics. After speaking with some companions of the branch it was happened to us that the best idea would be "integrated" into of the cabinet of a conventional amplifier; assured discretion and functionality; for which they provided 2 donors to me, two Sansui amplifiers model AU-X 517R; in addition and this way the amplifier
will have the same presence and ease of use of one commercial one of the high class, but the clean sound of the valves.


Just I said, I liked to create an original and different amplifier; already some years ago an old technician gave among other things a quartet to me of new valves PL36 and identical, these valves have bad fame in the world of the audiophile by their little linearity in the zone next to the cut in “normal” bias of G2, but on the other hand, in its leaf of characteristics according to a technical sheet of Philips origin a possible Push-pull configuration is suggested in way pentode with G2 fed 150V., anodes to 300V. and a transformer with an impedance between anodes of 3500 ohms obtaining itself this way something more than 40 W. with one lowers distortion, more than enough to me . Another added advantage of these valves in addition to his low price and availability is its big cathode, that guarantees a low internal resistance and correct operation with relatively low values of tension; I mean, little internal resistance, little excursion of gain by changes of impedance in the load = smaller necessity of feedback. For only technical reasons, since for the control of tones of the original amplifier it was to traves of the feedback of the power stage, it needed a great gain in open bow; therefore I have decided on valves ECC83 for the stages previous and driving; more concretely by their homologous Russians, the 6N2P, very good and to good price, the years of technician print a character eminently practitioner and free of odd habits and “labels”. Well, already we have the base, we have in addition a first sketch to scheme, that soon would be demonstrated inefficient, one very pretty “box” with decent preamplifier stages, an feeding that is not worth to me, but that I can redesign, desire and something of time, hands to the work.


First question, I need a power transformer,I rewind the original transformer with the voltages that I need.
Second question, I need output transformers, sockets, etc... I buy them on internet , good price..
Third question, I want a printed circuit, then it is not problem and I design it with the AUTOCAD, that is not the best application for these necessities, but is the better handling I know.
Fourth question: it is necessary to lodge all this within pretty "cabinet" making estimations of measures, needs of screening, perhaps the most boring part of the project, but with patience and paper sketches is carried out successfully.



Well, the power supply already is redesigned, the lodged elements, we have artisan printed circuit and lodged in its site; the preliminary tests that begin they will demonstrate that the first sketch does not work, too many stages connected with capacitors generate elf-oscillations to low frecuency = difficulties biasing the pentodes; in addition electromagnetic connections exist due to the space shortage reason why I must screen the triodes and modify the design. On the other hand curling in the sound is appraised reason why I rectify and I stabilize the filament voltage, being the set with this aspect.


Well, already we have something presentable, the successive improvements and modifications are having desired effect, the amplifier and as by magic art it is maturing from a strident sound initially distorted and unstable, to sound a devoid of background noise, absolutely clean and powerful. Impossible to mention here all the made modifications, but the aspect at the end of them is this.

Also is appraised the differences between this project and its transistorized twin brother, pretty, isn’t it ?



The penultimate chapter turn on the noises, hummings and other undesirable signals that is generated in all electronic circuit; in this chapter the fundamental thing turns out to be: the positioned election and of the grounds, the location of different wires, the shield of "sensitive parts", that the tríodes and the wires of feedback have turned out to be, that are of the armored coaxial type, to rectify and to stabilize the heater voltage and the use of quality materials, specially the resistance, better of metallic film. These will be the last tests in the experimental phase.

is appraised the later Vista with all the modifications already made Here; genuine home made flavour!



As opposed to a the one Here that will be its definitive lodging in substitution of home cinema LX-9000 Philips, discreet, isn’t it? I also enclose the definitive scheme that can be applicable to other projector with the necessary modifications and adjustments. I have not had time to pass it to the Autocad but it is understood.




We finish comparing the sound with its transistorized twin brother, is clear that the last one has more Watios, 70w. as opposed to 40w. by channel and is the this only section in which it surpasses the tube brother. The new creature [ b ] lacks noise![/b ], the sound is, fantasticly clean and is transparent, natural, giving to a sensation of clarity and great power to moderate volumes and with a smooth and progressive distortion to little recommendable volumes; it is pure tube amp, and I am enchanted with the new creature, who has surpassed all my expectations and to all the constructed tube creatures previously by my. So single she follows to him close by my other official tube amp, the Vieta A-217. And that is everything, I hope that you liked, I also hope that somebody is animated more with one project of these with recycled PL36 and/or of transistorized amplifiers. Contained costs and great guaranteed satisfactions.
Aitor Aurrekoetxea Cusumano