Russian spud amp

[Jaime]

http://audioportal.spb.ru/images/art...8/image001.gif

This is an 2 x 6C45pi 1~1.5w amp.
http://audioportal.spb.ru/amplifiers/p2_articleid/179

[ErikdeBest]

Hi Jaime

About two weaks ago my girlfriend and I were in Montevideo, to be more exact, in Solimar, visiting friends, but we have spent some hours in Montevideo to. We liked it, much more relaxed than Buenos Aires, were we had the unfortune to sleep in a hostel located at the 9th of July, with all its traffic.

Interesting schematic (simple, 1.5W isn't soooo low and it allows the use of a 220V->~9V toroidal for output). At first I thought it was a SRPP, but then I noticed the lack of the cathode resistor at the lowest tube... As the upper tube has (an adjustable) cathode resistor, the current through the lower tube will be limited anyway, but still, how does it bias?

And what about using a 12HG7 (or similar) instead of the 6C45P?...I have had more succes in finding 12HG7 in my stay in Brazil than the 6C45P (maybe that is also true for Uruguay) Also, 12HG7 use to be cheaper!

Erik

[Jaime]

The translation with Altavista.
Oh my God... this is terrible

“Concept
Amplifier circuit is sufficiently untypical; however, it possesses definite advantages over the more traditional version of single ended odnokaskadnika – as sonic, which will easily hear after assembling, so also by purely chart technology. In the amplifier the extended details and the lamps, to acquire which will not compose special problems, are used.
Let us pause in greater detail at the key special features. In order to obtain in the one-stage amplifier although the to any extent intelligible output power (i.e. more than 1 watts), it is necessary the lamp, which possesses the high strengthening (> 30) and high whereas steepness of the characteristics, and furthermore still and by largest possible dissipated power on the anode. Unfortunately, the selection of similar lamps is very small, especially this concerns Soviet reserves – from the triodes this 6С45П/6С15П… and, perhaps, all. Are other tetrodes, such as deservedly loved by many 6Ð*5П (3x, not enough strengthening for our purposes!) and pentodes –6Ж52П, 6Ж43П, etc. I personally stopped its selection at 6S45P-E – first, this is triode, in the second place, lamp proved to be sufficiently accessible, thirdly, me it seemed more simply in the work how the same 6Ð*5П – especially this it concerns the problem of the suppression of the parasitic self-excitation of cascade.

The zero bias
Further I please to glance at the diagram, good it is sufficiently simple. First, for sure all will focus attention on the absence of any displacement in input tube – and here there is no error, precisely, so it is planned. The majorities of the designers of vacuum-tube amplifiers have a habit to fear grid currents as the features of incense , and by all forces they try to drive in and so weak-current triode into the regime, in which the amount of displacement with the interest overlaps the maximum voltage of signal on the entrance. But in this case many forget, that the majority of the lamps possess the greatest linearity precisely in the region of zero potential on the grid, and high distortions, by which they traditionally frighten those interesting in regimes with the grid currents, can appear only in such a case, when the source of signal is not capable linearly to work on the low load, which the grid chain during the positive displacement is.
Computer sonic pays are the optimum sources of sounding for the work to the input cascade with the zero bias, since their linear outputs are usually equipped with buffer operational amplifiers. Depending on the type of established operatsionnika sonic pay can give at the output 30-70 mA of current, which with the enormous reserve overlaps the needs of grid 6С45П with the work for the region of positive stresses. Moreover the levels of the output signal of the majority of consumer sonic pays rarely exceed the scope 1,2 v RMS; therefore too far we with the zero bias nevertheless will not fall into the grid currents. By the way speaking, at the entrance of amplifier there is no volume control, since in view of the special features of diagram and source it to considerably more simply achieve directly on the quite sonic pay.
There is one additional very good occasion to use a zero bias in the one-stage amplifier. The higher the quiescent current, the greater the power we will obtain at the output – and taking into account that in the best case the discussion deals with 1-1,5 watts, each grain is here expensive. Moreover the large amplitude of signal current on pervichke of transformer contributes to the expansion of the frequency band downward, due to an increase in the induction (if, of course, transformer is calculated for this quiescent current).
Certainly, I repeatedly checked and compared different modes of operation of cascade - both to the rumor, in the blind test and with the attraction of additional experts and with the aid of the spectral analyzer. And version with the zero bias invariably left by conqueror. Try themselves.

SRPP in the output stage
Concerning another circuit solution. Originally I realized traditional single ended version, on the pair of sparallelennykh 6С45П to the channel. In spite of influential merits – high transparency and detail – this amplifier suffered the essential shortage of strip on LF, which was very noticeably even on the shelf ACE. Therefore during one excellent day (from the supply Of a. rezvy, thanks to it!) I altered amplifier on topology SRPP, and was voznagrazhden the completely staggering sounding, which 4 already in no way it expected to obtain from so miniature and, it would seem, elementary by the construction amplifier. Especially vpechatlili low frequencies – 4 never heard this quality of LF- range from my past one-stage distributions.
The reason for this radical change in the sounding proved to be simple. First, in this start transformer core does not experience the magnetizing actions direct current, flowing through the primary winding, which by the most beneficial means affects the band of the reproducible frequencies – moreover now it is possible to use transformers without the clearance, for example toroidal. In the second place, with the aid of the precise selection of the value of the decoupling capacitor it is possible to attain the lift in the low-frequency region, which compensate fors the limited strip of transformer. Finally, topology SRPP is differed from the single ended the fact that in complete agreement with principle of push-pull through the load "is pumped through" two times the larger signal current, which furthermore contributes to an improvement in the sounding.
The uniqueness of topology SRPP consists in the fact that it in its essence "double measure- single ended". On the grids of lamps – stresses opposite on the phase, lamps work in the reversed phase; however, in this case if we remove one of them, diagram will cease to work (in contrast to the the traditional push-pull). Moreover with the aid of the selection of the value of resistor Rak it is possible to obtain the completely different nature of spectrum at the output of amplifier – from the typical- the single ended to the more characteristic for the double measure, with the suppression of the second harmonic. The value of this resistor very strongly affects the nature of sounding amplifier; however, it cannot be said that some specific rating will be preferable for all cases of life. Since my musical predilections are sufficiently many-sided, as this resistor in me established the potentiometer, which makes it possible to obtain from 50 to 450 Ohm, and with the hearing, let us say, melodious and soft music I select its minimum value, and for the heavy and aggressively reverberating genres I prefer higher values.

Details and the elements
Briefly about the utilized details. As the output transformers will approach any standard – in me they work ТВЗ-1-6 (pair to the channel, pervichki in parallel, vtorichki consecutively), but it is possible to place ТВЗ-1-9 (desirable to preliminarily sort out its core "overlapping", or at least simple to remove nonmagnetic clearance), and also output from the old radio-gramophones. As the original alternative according to the idea it is possible to examine the toroidal power transformers of low power to 7-10 volts – some of them can prove to be completely adequately reverberating, at least, so assures Steve Bench (http://members.aol.com/sbench101/ ), and although 4 itself thus far were not checked in practice, but 4 I do not see reasons to it not to entrust.
Power transformer – Т��-31 or any other, which makes it possible to obtain 240-260 volts on vtorichke. the P- filter of special features does not have, are used the chokes Of dya2 from a standard number; however, any will approach, by inductance from 5 H and with the effective resistance of winding is not more than 250-300 Ohm, including the same OF TVZ-Y-9. The capacitance values of filter select themselves, in conformity with the effectiveness of the suppression of the net background – SRPP in this respect more priveredliv than traditional single ended cascade; therefore I placed electrolytes with the reserve, good "banks" to 1000 mkF/ya00 v nowadays are relatively accessible.
A separate question – isolating capacitor, here to it is worth relate with the attention, since the quality of sounding depends on it. I used polypropylene on 20 F, simply they were near at hand. Specific value can be calculated on the basis of the data of transformer or to select experimentally. Recently on the markets in the abundance appeared starting film capacitors, with capacity 15-100 mkf/450 v, here here they will be time itself.

[Jaime]

Elimination of the problems
Crucial point – as any lamp with the high slope, 6С45П is inclined to self-excitation (although are less than analogous tetrodes and the pentodes). For averting this it is necessary, in the first place, to use grounding the type "star", moreover to ground compulsorily all four outputs of cathode; in the second place, categorically I do not recommend to exploit amplifier without the anti-ringing100- ohm resistors in the grid chains. Pover'te, if they influence sound, then only in an positive manner – freeing us from the harmful parasitic oscillation of cascade. Even to the deficiencies 6С45П can be attributed tendency toward the microphonics, which is easy to otsledit', listening amplifier in the qualitative head sets (irreplaceable tool with the fixing) – this characteristic contrary ringing- itch on HF, especially if we knock on the housing of uslitelya. By easy rapping according to the balloons you will determine the ringing lamp and you will replace it, and in order to avoid similar problems, you fasten power transformer on the chassis through the vibration damping padding, and lamps are better to establish in the panel with the dampers.
Ways of the improvement
If to you is pleased sounding the amplifier, assembled "on the knee" from the details from the radio-market, there is sense to think, also, about the more qualitative realization of this concept. As can be seen from diagram, versions for the improvement this amplifier although detract. First, this concerns nourishment – the application of rectifier tubes or tube diodes, G- filter and/or stabilizer of anode voltage out of any doubts beneficially will affect the quality of sounding. Also is worth poeksperimentirovat' with the filament circuit – it exists the opinion that the rectified and stabilized filament current improves the quality of reproduction, and in this there is the specific logic. Finally, in the diagram an actually minimum quantity of details, and is worth using the same of the highest quality.
By one additional interesting, but ambiguously received in audiokrugakh way of improving this construction is the replacement of all resistance network elements inductive – audiodroselyami. This concerns the resistor of grid leak, instead of which it is worthwhile to establish the transformer- attenuator, in the ideal which increases 1:1,5, and also resistor Rak. However, this exactly are that case, when experiment it says more than any theoretical explanations; therefore somehow attempt to estimate sounding this diagram, after connecting instead of Rak the primary winding of qualitative ТВЗ
Finally, for obtaining the uncompromising sounding of this amplifier will be required special output transformers – in the catalogs of producers they usually they are designated as parafeed transformers. Basic difference from the traditional single ended – the absence of nonmagnetic clearance, and in certain cases and addition to the core of Permalloy, which makes it possible to obtain very large inductance and, correspondingly, to maximally enlarge the frequency band and the quality of reproduction. But this will already be not the "near-computer" amplifier, connected to the inexpensive shelf ACE, but the device of other entirely class and price category.
Epilogue
My amplifier thought and was carried out as the super-budgetary solution of the problem of the qualitative sonification of work site, precisely, therefore in it are used only extended details, and chassis, as it is relied to "near-computer" device, it is prepared from the housing of old net switchboard 10- Mbit, which in the abundance are dragged along in podsobkakh and storeroom system administrators with the period. It appears, of course, it is stern;; however, and the destination of it – to serve as delight not for the sight, but for the rumor, but already it completely manages this function.
Like everything. For a period already of more several months this amplifier is my dear, worker on 10 is hour in a 24 hour period, and standard – with it I simultaneously compare sounding its other constructions, and they be inferior the same to it, I pitilessly investigate them on the spare part. For this reason at the present moment this amplifier still continues to remain my only, in spite of the rarely cooling soldering iron�