The power amplifier on two 6p45s was developed for everyday work on the air. In addition, it can be recommended for repetition for novice shortwave radio amateurs. The amplifier uses 6P45S tubes, which are available, have good linearity and a huge working life (5000 hours). They can be used even after many years of work in the horizontal scanners of TVs. The power amplifier for two 6p45s has an output power of 200 W on all HF bands with an input power of 30 W and is assembled in a case available to the author with dimensions of 193x393x270 mm.
Often novice radio amateurs (and not only) purchase an inexpensive imported transceiver that does not have a built-in antenna tuner (automatic matching device). Proceeding from this, a circuit for switching on lamps with a common cathode is applied to the power amplifier on two 6p45s, in which the excitation voltage is supplied to the control grid. The amplifier allows you to “unload” the transceiver by decoupling it from the antenna. In fact, as they say now, this is an active antenna tuner. Among other things, the transceiver is protected from static electricity charges on the antenna terminals and other troubles associated with this (for example, an antenna breakage or short circuit in it). In the event of a lamp breakdown (an unlikely incident when using 6P45S lamps), such a circuit solution is much safer for the transceiver than a circuit with common grids.
A schematic diagram of a power amplifier for two 6p45s is shown in the figure. The input signal through the HF connector XW1 and the contacts of the K1.1 relay is fed to two low-pass filters with a cutoff frequency of 32 MHz, which are made in the form of P-circuits, the input and output resistances of which are 100 Ohm. At the input of the amplifier, the P-circuits are connected in parallel, therefore, the input impedance is 50 ohms. The circuit lacks capacitors with a capacity of about 60 pF included in the low-pass filter. In reality, these capacitors are formed by assembly and other capacitors. The input capacitance of the low-pass filter is formed by the capacitance of the coaxial cable, through which the output of the transceiver is connected to the input of the amplifier, as well as the capacitance of the mounting and the capacitance of the contacts of the relay K1.1, which in total is 120 pF. The linear capacitance of the RK50-3-13 coaxial cable is 110 pF / m, therefore, the length of the cable connecting the transceiver to the power amplifier for two 6p45s should be about 90 cm.More precisely, the cable length is selected to minimize the SWR when setting the power amplifier for two 6p45s.
The output capacitance of each low-pass filter includes the input capacitance of the lamp (55 pF) and the mounting capacitance (approximately 5 pF), for a total of 60 pF. The use of a low-pass filter is useful for several reasons at once. Firstly, to reduce the level of higher harmonics, and secondly, to compensate for the capacitance of the coaxial cable connecting the amplifier with the transceiver, the length of which should not exceed 0.1 of the shortest wavelength of the amplified signal, i.e. 1 m. When this condition is met, the cable is a capacitance and does not transform the input impedance of the amplifier. Third, the low-pass filter compensates for the input capacitance of the lamp, as a result of which the input impedance of the amplifier becomes frequency-independent, and the amplitude of the exciting signal does not decrease with increasing frequency. It is obvious that the use of a low-pass filter is justified.
The LPF outputs are loaded with resistors (R7 and R10, respectively). From these resistors through the capacitors C7 and C9, the alternating high-frequency voltage is supplied to the control grids of the lamps VL1 and VL2. The gain of each lamp is 6.7 times the power (approximately 8.2 dB). This, of course, is not much and is comparable to the gain when working with tubes with common grids, but it is justified by the very stable operation of the amplifier. In addition, its entrance part is simplified. The task of filtering side oscillations at the amplifier input was not set, since the output circuits of the transceiver handle this, although some filtering of the higher harmonics does, of course, take place.
Such a construction of a power amplifier for two 6p45s has another advantage, which is that the passage capacities of the lamps are not summed up, which happens when the lamps are connected in parallel. Therefore, the stability of the amplifier is further improved.
The use of a switchable anode choke in combination with other measures taken made it possible to obtain the same output power (200 W) on all HF bands. Throttle DrZ and capacitor C12 serve to protect the power supply in case of possible self-excitation of the VHF amplifier. An RF voltmeter is installed at the output of the P-circuit for ease of adjustment. In transmission mode, when the pedal is pressed, an electronic key is triggered, made on transistors VT1 and VT2. Transistor VT2 opens, and relays K1 - short circuit, included in its collector circuit, are triggered. The contacts of the relay K3.1 (Fig. 2) are switched, and the supply voltage is supplied to the screen grids of the lamps from the voltage stabilizer made on the transistor VT1. A parallel regulator that protects lamps against the dinatron effect of the anode or screen grid, despite its simplicity, works well. Resistor R9, which is connected to the output of the stabilizer, facilitates the thermal mode of the transistor VT1 in the receive mode.
Of course, it would be possible to use a parallel-serial voltage regulator, which is more economical than a parallel one, but also much more complicated, since contains actually two stabilizers. Such a constructive complication with not very significant savings, according to the author, is inappropriate. The operation of the stabilizer can be improved by using a light bulb for the corresponding voltage and current instead of the ballast resistor R5, which will play the role of a barretter, increasing the stabilization coefficient. In fact, a parallel voltage regulator is just a powerful high-quality zener diode, the current through which (62 - 70 mA) is set using the ballast resistor R5.
The power transformer Tr1 of the power supply is connected to the network smoothly, through the limiting resistor R1, which, some time after switching on, is short-circuited by the contacts of the toggle switch B1 with the middle neutral position. Such a simple switching circuit significantly prolongs the life of lamps and power transformers, and indeed the entire amplifier as a whole. It is known that a cold lamp filament has a resistance ten times less than a heated filament. Consequently, the starting filament current of the lamp is ten times the rated filament current. A large inrush current when the voltage is applied overloads the filament, destroys its structure and reduces the lamp life. Therefore, the use of soft start is more than justified.
At the input of the power transformer, a line filter is installed, made on two winding choke Dr1 and capacitors C1 and C2. The anode power supply is protected against overcurrent. Resistor R11 (Fig.) Limits the current in case of breakdown or short-circuit of the output of the anode voltage source at the level of 600/10 = 60 (A). The diodes of the FR207 type used in the power supply (Fig.) Will withstand this current pulse and will not fail. Anode voltage source is composed of two, 300 V each, connected in series, which improves the dynamic characteristics of the power supply.
On the rear wall of the case, a power amplifier for two 6p45s, opposite the 6P45S lamps, is equipped with an M1 fan for a voltage of 24 V, operating for an exhaust hood. It turns on when the power amplifier is operating for a long time with the B2 toggle switch. To reduce acoustic noise, the fan is powered by a voltage of 20 V. The fan is fixed through a pad made of soft felt. In addition, the screws securing it to the back wall are equipped with polyethylene tubes and two washers made of felt and textolite. Thus, the fan casing is completely insulated from the metal surface. If a fan with a plastic casing is used, this is desirable, and if the casing is metal, then such a fastening is mandatory. 6P45S lamps are installed on a double-sided fiberglass plate, under which a 125 × 65 mm cutout is made in the chassis. All voltages are supplied to the lamps through feed-through capacitors (except, of course, the excitation voltage, which is supplied by a coaxial cable about 4.5 mm in diameter with fluoroplastic insulation). Relay K1 is located near the input connector XW1 (fig.).
All parts related to the high-frequency unit are interconnected by 20 mm wide tires, which are cut from tinned tin from cans of instant coffee. Cathodes of lamps, current collectors of variable capacitors included in the P-circuit, antenna connector, “ground” terminal, blocking capacitors in the anode choke circuit are connected to the busbars. Especially carefully it is necessary to connect to the bus the current collectors of the KPI, the grounded terminals of the additional capacitors connected to them, and the cathodes of the lamps. Considering that a large loop current flows between the grounding points of the KPI and the cathodes of the lamps, other parts that go to the body should not be grounded between them. Due to the large total output capacitance of two 6P45S lamps (about 40 pF), a significant part of the loop current (about half at 28 MHz, much less on the low-frequency ranges) flows through the section of the bus between the anode KPI and the cathodes of the lamps.
The inductors L1 and L2 of the input low-pass filter contain 12 turns of PEV-2 1.2 mm wire. Winding diameter - 10 mm, length - 20 mm. Frameless winding. Both LPFs are enclosed in one common screen and are located under the chassis, near the lamp panels.
All inductors of the P-circuit are wound in one direction, the taps are counted from the “hot” end. Coil L3 - frameless (diameter - 26 mm), wound with a silvered wire 03 mm on a mandrel, winding length - 30 mm, number of turns - 4. Anode KPI, which is one section from a two-section variable capacitor of the old model with a gap between the plates not less than 0.5 mm, soldered to the branch from one turn of the coil L3. This connection reduces the effect of the initial capacitance of the KPI on the resonant frequency of the P-circuit in the 28 MHz range.
Coil L4 - frameless (diameter - 40 mm), has 4.5 turns of PEV-2 wire 02 mm, branch - from the 3rd turn, winding length - 27 mm. The L5 coil is wound on a 45 mm frame and contains 5 + 5 turns, the wire diameter is 1.5 and 1.0 mm, respectively. The winding step is 5 mm, the winding length is 50 mm. The anode choke is wound on a fluoroplastic rod with a diameter of 18 mm, the length of the winding is 90 mm, the wire is 0.4 mm, the outlet is from the middle.
Power transformer Tr1 is made on the magnetic circuit ШЛ32х40. Its coil data are shown in the table. 
The line filter choke is made somewhat unusual. It is wound with a double mains wire from a burnt out electric soldering iron on a ferrite rod of 08 mm from the radio receiver's magnetic antenna. The length of the rod is at least 120 mm. Before winding, the ferrite core is wrapped in several layers of varnished cloth. At first, the choke is wound as usual, but when the winding reaches the middle of the rod, the winding direction is reversed. To do this, in the middle of the choke, the wire is bent, the loop is fixed with a strong nylon or silk thread. Then, if the winding was carried out clockwise, after the middle of the length of the rod, it is carried out counterclockwise. The inductance of the choke remains large enough, but the magnetization of the ferrite rod and its saturation due to a possible insufficient cross-section is completely excluded. Consequently, all non-linear effects and changes in the inductance of the inductor are completely excluded when the load on the line filter changes.
The power amplifier for two 6p45s operates in class B. The quiescent current of the lamps (80 - 100 mA) is set using a variable resistor R13. The bias voltage is about -45 V. The use of additional resistors R14 and R15 completely eliminates the erroneous setting of the bias voltage and its disappearance when the contact in the variable resistor R13 is broken.
At the input of a power amplifier on two 6p45s, between the connection point of the lower (according to the diagram) terminals of the coils L1 and L2 and the common wire, a capacitor with a capacity of about 120 pF is installed, made up of 3 KT-2 capacitors. The capacity of this capacitor is specified when the amplifier is tuned in the 28 MHz range according to the minimum SWR in the cable connecting the transceiver to the power amplifier. It is advisable to carry out the adjustment with well-warmed lamps. The LPF is adjusted by selecting the inductance of the coils L1 and L2, as well as the length of the cable.
The P-circuit must first be set up in the “cold” way. The stand layout is shown in Fig. 3. When adjusting the P-circuit, one should not, as some authors recommend, turn off the lamps and the anode choke and replace them with an equivalent capacitance. Firstly, it is difficult to accurately measure this capacitance, and not all radio amateurs have a capacitance meter, and secondly, the anode choke in the parallel power supply circuit is connected exactly parallel to the P-circuit coils (by means of blocking capacitors C12 and C15). Consequently, a circulating reactive current flows through it, depending on the magnitude of the alternating voltage at the anode of the lamp and the inductance of the choke itself.
As you know, when two (or more) coils are connected in parallel, their total, total inductance decreases and becomes less than the inductance of any of the parallel-connected coils. It is clear that the greatest decrease in the P-loop inductance will occur in the 1.8 MHz range. At 28 MHz, the influence of the anode choke on the decrease in the inductance of the loop coil is insignificant, is within the error limits of the measuring instruments, and can be neglected.
If the coils L3 - L5 are made exactly as described, tuning the P-circuit is reduced to checking the resonance in the middle of each range. For this, a heterodyne resonance indicator (GIR) is suitable, which, despite its simplicity, is a universal high-frequency device and is completely undeservedly forgotten at the present time. Do not forget about the neon lamp, which, being fixed on a long fiberglass rod, is an excellent peak indicator of high-frequency voltage and allows you to accurately determine the moment of precise tuning of the P-circuit to resonance, or, for example, the appearance of self-excitation. By the color of its glow, you can approximately determine the frequency of self-excitation. At the operating frequency, the glow of a neon lamp has a yellowish-violet color, and when self-excited on VHF, its glow takes on a bluish tint.
The anode current of the lamps with a detuned P-circuit should be about 600 - 650 mA, with a tuned P-circuit - not less than 535 - 585 mA, i.e. The “dip” of the anode current during the P-loop tuning should not exceed 65 mA, because in this case, there is a redistribution of the anode current “in favor of” the current of the screen grids of the lamps. Consequently, a higher current of the screen grids will cause their power overload, which is undesirable.
You should not aim for more than 200 watts of output power. Nevertheless, by increasing the anode voltage to 900 - 1000 V and accordingly changing the data of the P-circuit, in SSB mode, an output power of 300 watts can be obtained. But the reliability of the amplifier in this case decreases, tk. the maximum permissible power dissipated for a long time at the anode of one lamp is only 35 W. Therefore, it is not recommended to use this mode, and the difference in the level of the emitted signals is not so great.
I propose a well-developed low frequency circuit for 6p45s, with a five-band tone block. The amplifier is made according to the classical single-ended circuit based on A. Manakov's circuit. In the description of the work, the diagram is unnecessary.
LF tube amplifier
During the assembly and adjustment process, some resistor values were changed. During the setup process, you will need to select R23, R34 so that the voltage at the 6p14p anodes was 190V. Then, by selecting R45, set the anode one to 6n3p 90-110V. You may have to choose the resistance R22, R33, the voltage at pin 9, set 90V. The negative voltage on the control grid 6p45s can be from 45 to 70V, it all depends on the lamps used and the degree of wear. For me, this value is 54v. This concludes the whole setup. 
Tone block
I used a BA3822LS circuit as a timbre block. This microcircuit has good parameters and is commercially available. We have 69 rubles. The advantages of such a circuit design are the absence of a heap of shielded wires and screens; in the absence of a signal, no background noise and hiss are observed. It is advisable to connect the finished tone block to the low frequency input through trimming resistors of 100K, because the microcircuit has a sufficiently high gain level.
Initially, instead of a microcircuit, I used a similar circuit on two 6n3p lamps, but in the end I abandoned it due to the impossibility of getting rid of interference and background due to weak shielding of the lamps and the entire circuit due to insufficient space in the case. I note that the block of adjustments on the lamps still sounds warmer as it seems to me. For those who are interested in this option, the diagram is also attached.
Amplifier power supply
Now about the power supply. A ready-made ts270 transformer was taken, only slightly winding turns over the existing windings. Droseli were taken ready from ... I don’t remember what. Or from a b & w TV set or a receiver .. it is desirable to organize a separate power supply for each channel to reduce interference and distortion between them.
I used one rectifier in both channels. There was no particular desire to wind another winding, in general, as well as wires in particular. I paid more attention to replacement capacitors. Nothing of the kind was noticed, it cost one step-up winding. Self-made output transformers, such as ts-20 ts-30, whoever has what they have, with a horseshoe-shaped core.
We wind in this way: the primary coil is 94 turns with a wire of 0.47, then 900 turns of the primary coil with a wire of 0.18 should turn out like this 94/900/94/900/94 /. We connect the primary to the last secondary in parallel, between the halves of the iron no paper gaskets are inserted. We smear with a supermoment (second glue), collect and put a bandage on top of the iron, if there is one, if not, then clamp the iron until the glue is completely dry.
The plus of such a solution is that it does not make noise during operation (provided that there is good iron and tightly packed windings), the iron is securely held and, if necessary, can be easily disassembled - it is enough to hit the place of gluing with something heavy. For the case, I used 3mm aluminum sheets. Adjustment knobs are decorative duralumin knobs for furniture doors, holes are drilled to the desired diameter and shrink-wrapped directly onto the change-overs.
The body is painted with auto enamel and half is pasted over with a wood-like film. I made the power supply transformer external in order to reduce its effect on the low-frequency filter. Trans packed into a case from the power supply unit of the old kopma, connected to the amplifier with a 6-core cable through the connector on the unch case. The cable is assembled by hand. There is an inaccuracy in the scheme R40 AND R29 REGULAR MLT-2, and HERE R28 R39 must be five-watt!
Comments (28)
Uv. Sam! Can you indicate the output power of this ULF?
Thank you.
yes, of course. in this version 12 watts per channel. in triode mode 24 watts per channel. pins 3 and 6 are connected directly to the positive power supply. and the bias voltage is selected. made a quiescent current of 100 ma. in triode mode, nonlinear distortions increase. and 12 watts is enough for 100 watts acoustics
12 watts is enough for 100 watt acoustics
You want to say that such an amplifier with only 12 W leash will swing my S90s, something I don't understand ...
if your acoustics is not S-90, then everyone else pulls with a bang. I would have demonstrated the opportunity. Of course, the main and main condition is a properly wound weekend trances.
s-90, although they are considered, if not one of the best acoustics of domestic production, their sensitivity is very low
but if there are no other columns, then you can slightly pick up the number of turns of the secondary.
Good day to the author
There are a couple of misunderstandings with the scheme
1 Input left right goes to R52 and R53 are these central cores, and the common core sits on the ground?
2 there is no information about the 6.3v filament power supply, how many are there for each type of lamp its own block?
3 in the diagram shows where to supply power -70 and +350, and +70 and -350 go to the circuit or not? some of the terminals are unsigned (end R29 R40)
Good day! I was interested in your article, I want to make the same amplifier, but I did not understand how to wind the output signal transformer from the lamps (there is no experience in this).
As I understood from the description, the power transformer and the output are combined or what?
I used one rectifier in both channels. There was no particular desire to wind another winding, in general, as well as wires in particular. I paid more attention to replacement capacitors. Nothing of the kind was noticed, it cost one step-up winding. Self-made output transformers, such as ts-20 ts-30, whoever has what they have, with a horseshoe-shaped core.
Quote:
We wind in this way: the primary coil is 94 turns with a wire of 0.47, then 900 turns of the primary coil with a wire of 0.18 should turn out like this 94/900/94/900/94 /. We connect the primary to the last secondary in parallel, between the halves of the iron no paper gaskets are inserted.
From the description, I did not stick where the secondary, and where the primary, since there are two of them in the description. If possible, please write a little more about the weekend trance or correct where the error is. Thanks a lot!
P.s. Yuri
Where 70 and 350 V are written, conclusions. Pay attention to which of them are grounded, this is not a minus, but the author had in mind the dash.
I answer for Yuri. first: yes, the braid, she's a common vein sits on the ground. second: the power supply is made on a ready-made transformer from a bw box, type TS-270. (270 watts). All windings on this transformer can be left. you just need to wind up the secondary winding so that the output changes are 300-320v. those that are on it give 220, this is not enough. for heating we use the native winding. it will completely pull out 5 amperes. all the filaments of the lamps are connected in parallel. third: the winding is 70v, plus is connected to the ground common wire. -350 we apply to the ground wire according to the scheme. I didn't sign, I thought there would be no questions, everything seems to be obvious.
in the description above, I mentioned TC 270 and that it was taken from a bw lamp box. it has all the windings, in the absence of a 45 volt winding on this trance, we finish it ourselves
70 we serve where it is -70 on the diagram is not a dash
for ALEXEY .. one power transformer is not in the photo, it is packed in an old case from a computer power supply, I wrote about this. and two weekend trance. For an output trance, it is best to take a trance with a horseshoe-shaped core, the same as that of the TC270, only smaller in size. If there is no such transformer, as I wrote above TC20 or TC30. then you can take any other with an approximate power of 30-40 watt, with W-shaped iron. Why is the horseshoe-shaped iron better., because four finished horseshoes have already been glued together. The w-shaped is bad because if the plates have burrs, rust is crumpled, then in the assembly they will shorten among themselves, due to the fact that the insulation is broken. such a trance will not work as it should, and will not bring anything but disappointment. a prerequisite for such iron, unbroken plates. if there are no trance ts, then you can take ready-made factory type TVK-30. the iron is the same. but you will have to sweat to disassemble them, because they are filled with paint and, in the worst case, epoxy. Now about the winding. First, 94 turns of the secondary winding are wound, the one to which the acoustics will be connected, then a layer of insulation, then 900 turns of the primary winding, then a layer of insulation , in the end you should have three secondary windings independent of each other and two primary windings. you draw conclusions from each thread, so that you can connect them as needed. connect the secondary windings in parallel, just do not confuse the beginning and end. beginning with beginning end with end. and the primary windings are connected in series, starting one with the end of the other, as a result, one primary winding will turn out. and one secondary. Well, it seems like it is nowhere clearer. there is nothing difficult even if you have never done something like this
hint. if you can not get rid of the background AC in the speakers. then look at the diagram with the name: entry-level vacuum tube, there is a circuit in the circuit design, which completely eliminates this problem. this scheme can be easily found through Yandex.
Realistically, with this lamp of high-quality sound 6-7 watts, the slag is higher.
for Vlad. most often, slag is obtained from the fact that they use poor-quality elements, there is no knowledge, skills, and even more often from hands.
There is a significant jamb in the scheme. Anode load 6P14P - 22kOhm, which is much more than optimal. This greatly increases the output impedance of the driver, making it a little pleasant for the output tube. And also the distortion of the driver is greatly increased.
The 6P45S lamp has a huge slope. This means increased distortion.
Indeed, at a power of more than watts, these distortions are both audible and visible even on the oscilloscope screen.
for sound .. everything you wrote is in theory .. here everything was selected manually and it was the 22k anode resistor, try to assemble it yourself first, check it and then criticize it. for each 6p14p the value of the anode resistor turned out to be different. and everything was tuned by an oscilloscope.
Sergey, all the answers to your questions are given in the following picture (click to enlarge the picture):
Hello, please tell me what the problem is: I assembled such an amplifier, but one channel is louder than the second. It turns out that the channel in which the 4.7kΩ resistor is installed works louder.
Hello. Try to swap the inputs of the amplifiers connected to the 1x250 pass-through capacitors (C1, C26) - if another channel now becomes louder, then the reason must be looked for in the signal source, signal wires or the preamplifier circuit on the 6N3P tube.
The circuits of the LF power amplification channels on 6P14P and 6P45S tubes are completely the same. If they play at different volumes, it is possible that faulty or damaged electronic components are installed somewhere.
For example, to select R23 and R34, which are 22K each, you can take a variable resistor of 36-56K, set its slider to the position to obtain a resistance of 22K. Then you turn on the circuit, measure the voltage at the anodes of the lamps, as indicated in the article, slowly rotating the handle of the variable resistor, you achieve the desired readings of the device. In place of the variable resistor, solder a constant one with the same resistance.
“Messire, why are monsters? They are heavy, huge, and radiate intense heat. " To begin with, the magazine you are reading is not audiophile after all. What is audiophilia? This is a hobby for canned (in a good way!) Sound. The click of the power switch and ... enchanting sounds poured out.
Not from Edison's roller, not from a gramophone and not from a gramophone, but from yours, namely your acoustic systems. But how to achieve magic, or enchantment with sound? Of course, using the appropriate components of the sound reproduction system. Let's not talk about turntables and speakers, let alone gold-plated cables and silver chassis.
Let's turn our attention to the amplifier circuitry. In the old days, in our vast country, all efforts were spent on "defense." Individual enthusiasts have taken care of the issues of high-quality sound reproduction. There were few publications. The main achievements were obtained not with us, but somewhere overseas.
The main sources of information are also located there. Who have heard before about Cucing'a triode amplifiers, the famous D.T.N. Williamson'e or that the local transformer OOS in the cathode of the pentode was suggested by Peter I. Walker at f. Acoustical manufacturing, producing products under the Quad brand? Something has appeared in recent years with us. Although the information is still not enough.
- Firstly, these are lamps.
- Secondly, these are triodes.
- Thirdly, it is - (God forbid!) - not to use negative feedback (OOS) and class "B" (only "A"!).
Fourth, the simpler the circuit, the better it is. “One-stroke” is better than “two-stroke”.
Unfortunately, I was not able to hear the actual “Ongaku” work. Among my acquaintances, there was no owner of this wonderful device from Audio Note. And all kinds of "Surf" and even one "Luxman" on the lamps sounded somehow equally "dull", and did not make an impression. But then, once, a familiar audiophile complained that the tube amplifier, which he assembled with his own hands in a year, did not justify expectations, did not "sound" and did not even give the required power.
I helped him adjust the lamp modes, reduce the background and get an output power of 6 W per channel, and also introduced a switchable OOS from the output to the input stage, i.e. covered three stages with it, which is often done in tube amplifiers. In addition, I added an RC circuit at the output (Zobel circuit) to eliminate RF oscillations at idle. For instruments, it turned out approximately the same settling time as without OOS, and the same exponent.
And so, we are listening to this amplifier. Sounds great! Deep, without reference to the speaker, surround sound is simply mesmerizing! We turn on instead of this tube "monster" American "Harman Kardon" (NK-1400) - transistor with OOS ("inexpensive", only $ 700). The sound is noticeably worse than that of a homemade one - there is no such volume and depth. We are launching the domestic lamp "Surf 50 UM-204S". The sound is even more “dry”.
Finally, the most decisive experiment. We turn on the OOS in a homemade lamp. At the same time, the bandwidth expands from 30 kHz to 100 kHz, the output power increases to 12 W with the same harmonic distortion (about 3%), and the output impedance decreases. Everything seems to be fine, but the effect is amazing! The sound becomes the same. as well as in “Priboi”. The charm is gone, the sound is "dry", there is no volume. not to mention the small details.
I don't want to listen. We remove the OOS - and the "magic" is restored! Again, I don't want to turn off the amplifier. I would have listened and listened ... Then we compared its sound with the sound of the Orbit UM-002 Stereo amplifier copied from the Quad-405, and found that Orbit was in the same place as the NK-1400, but the place is much lower than the homemade lamp.
It should be noted that the listening was carried out in the same room of 16 m², with the same acoustic systems, with the same CD player, on the same discs (test, jazz, choir, vocals, symphony orchestra ).
The self-made amplifier is I. Morrison's amplifier, adapted to our configuration by A. Bokarev. I present this simple circuit (Fig. 1) with the OOS circuit, which improved the objective technical parameters, but “spoiled” the sound. The amplifier uses a case and transformers from the UZCH "Priboy 50UM-204S".
The supply voltages turned out to be slightly less than indicated in. The power output was also lower. What is the use of triodes instead of pentodes in the output stage? Rather, 6P45S lamps in triode switching, in class “A” and without OOS. In class “A”, the output power is significantly reduced at the same supply voltage, compared to class “B”.
But for high-quality sound in small rooms (16. ..18 m²) and with speakers with a high output 6… 8 W per channel is quite enough. A triode connection gives a lower harmonic distortion than a pentode one, times 2 -5% and 10%, respectively (without OOS) at optimal load, and even less with an increase in the load reduced to the anodes, but at the cost of reducing the output power.
The internal resistance of the triode (Rj = ∆Ua / ∆Ia) is much less than that of the pentode. This can be seen from the given anode characteristics of the GU-50 (P-50, LS-50) pentode (Fig. 2). In a triode connection, the GU-50 and 6P45S have practically the same output characteristics. For 6P45S in a triode connection, they are given in.
The use of an output transformer designed for a pentode and having a high inductance of the primary winding makes it possible to greatly expand the frequency response towards low frequencies, since The Ri of the triode is several times smaller than the Ri of the pentode. For the same reason, the effective capacitances of the windings are recharged faster, and the frequency band expands to the high-frequency side.
The small Ri of the triode gives a low output impedance even without OOS, although the low frequencies are somewhat emphasized. And finally, the most important thing. The absence of OOS gives a purely aperiodic transient process, without pulling and fluctuations (tyst = 10 μs to 99% of the steady-state value of Uout). The introduction of a resistive OOS with a depth of 20 dB (only resistor R7 is turned on) leads to large fluctuations in the transient response (CT). The oscillation amplitude reaches 60% of the pulse amplitude, and the oscillation period is 6 ... .7 μs.
Turning on the capacitance C2 = 1500 ... 2000 pF eliminates oscillations, the process becomes similar to exponential, tyst 5 μs. Oscillations with a period of 6 ... 7 µs indicate the presence of a resonant maximum or a dipole on the Bode diagram at a frequency of about 150 kHz, which can cause a delay in the HRC and “spoil” the sound. So choose! Or efficiency like a steam locomotive and great sounding, or good performance and a desire to turn off the amplifier as soon as possible. Low efficiency will not frighten audiophiles. Their slogan is: sound quality - at any cost!
I present my version of a single-ended amplifier on a 6p45s tube. A. MANAKOV's scheme is taken as a basis
I couldn't find 6p5p, so I decided to try 6p15p and 6p14p. It seemed to me that the 6p14p sounds better, and besides, it is more accessible.
The 6p45s lamp at a fixed bias does not behave stably (current is floating). With autobias, high power dissipation across the cathode resistor. I chose a compromise option - semi-automatic offset.
The 150 ohm cathode resistor is shunted with a 2200mkf * 35volt capacitor. A negative bias is applied to the grid from a separate low-power transformer (you can wind up an additional winding on the TS-180). I used a 12V trans from a low-power power supply unit (50-200mA) and connected the secondary to a 6.3v filament winding.
The TS-180 was used as a power one. The best option: using two TS-180s (two monoblocs) or one TS-270.
Amplifier circuit
As a holiday, you can use the TC-180 without rework, but it is better to rewind, since without rewinding there will be a recession along the top and bottom. The primary winding (750 turns on each coil, wire diameter 0.3-0.35 mm) is located between the parts of the secondary (120 + 120 turns on each coil, diameter 0.6-0.7 mm). Two primary windings are connected in series, four secondary - in parallel (for a load of 8 ohms). It is better, of course, to purchase a branded trance, but it costs money and not small ones. You decide. Many people think that TC-180 iron cannot be used to make a good trance. Maybe this is not ideal, but for free ...
Nevertheless, this is what happened - Fn-23Hz. Fv-26000Hz at -1db. Measured at 4 watts. Power up to limitation-8W. Maximum-12W.
Found Klaus's article "Fixed Offset Options" and decided to experiment with 6n45s. The result is pleasing. Option for 6p45s -125 volt bias voltage is fed through a 72 volt zener diode. When the mains voltage changes from 160 to 250 volts, the power at the anode remains practically constant.
CONFIGURATION. The adjustment consists in the selection of the resistor R4 in the circuit of the 2nd grid 6p14p according to the maximum gain and adjusting the anode current 6p45 with the trimmer R10 according to the voltage drop by R9 - 0.165 volts.
Comments on the article:
Background of the project.
Once they brought me a variety amplifier, two-channel. His age is 15 years old, made in Ukraine.
Rack case, height 4U (178 mm), depth 370 mm. Inside there are 8 pieces of 6P45S, 2 pieces of 6N1P, 2 pieces of 6N6P. Cooling with a noisy fan from a kitchen hood. The front panel is labeled 300 + 300.
Just what?
The power transformer, common to both channels, is wound on iron from OSM-0.4. Given that only the incandescences here consume at least 140 W, how much power does the anodes of the output lamps get and how much output power can be obtained from this, taking into account the efficiency? 100 W per channel, no more. In addition, the amplifier was made badly, and was inoperative, it was, in general, rubbish. The meaning of the further use of this construct is limited by the volume of the box, the output transformers included in it and the budget.
Taking all these factors into account, the task took on the form of “do something”, as an alternative to throwing away the old box and buying something else.
In the process of clearing and analyzing the design, it became clear that due to budget constraints, it was impossible to fully realize what the hull volume and layout allowed. Therefore, the upgrade project was immediately incorporated into the upgrade options (for example, space was left for an additional power transformer). As a result, the following scheme was assembled on this construct, without claims to originality, almost repeating the original in structure.
Only the simplest LED indicators of signal presence and overload are not shown, they have not undergone changes and work from the secondary of the output transformer. All resistors MLT, OMLT, S2-23. Resistors R3 and R7 have a power of 1 W. Resistors R10 - R13, R16, R26 - R33 have a power of 2 W. Film capacitors K73-9 and K73-17.
Cooling is carried out by a computer blowing fan powered by an additional small transformer with a diode bridge and a capacitor. Some of the elements and their denominations went "by inheritance", some are due to the contents of the "bedside table".
First turn on. Warm-up, offset setting. There are no obvious problems with self-excitation, which may arise when using 6P45S lamps. The background is within reason, especially taking into account the stage purpose of the device. The resulting sound cannot be called the height of perfection, however, this is already something! Now the owner can decide for himself how much he needs all this and, with a positive answer, invest in improving the apparatus, within reason, of course.
Upgrade
The first step is to deal with power transformers. The first option is to add one more piece of OCM-0.4. On two such pieces of iron, it is already possible to more or less realize the power potential, and the induction can also be reduced. The second option is to replace the existing enforcer with three toroids. One for heating + offset, two identical anode ones, and the latter have only one secondary (simplification of the coil product in this case is useful and relevant). Further, we add capacities to the anode power supply of the output stage, up to 2 ... 5 mF in each floor. We replace all film capacitors with "more decent" ones, increase the C4 and C5 values to 1 ... 2.2 μF. We correct the driver operating modes for 6N6P. Setting up feedback. Don't forget the bias chain. It can be made more reliable. Input and output connectors, regulators ... there is no limit to perfection. When building a structure without "hereditary" restrictions, you can try to make the anode rectifier in the form of a doubler instead of two bridges. This further simplifies the anode transformer, which, I remind you once again, must be of sufficient power. A slight increase in the voltage of the lower floor will then allow the use of an electronic choke to power the screen grids of the output lamps. The electronic choke can be different for each channel.
P. S. The above scheme, taking into account the recommendations, with a decent implementation, can play quite well. And loud. From this design, you can get a power of the order of 120 ... 160 W per channel. Attempts to squeeze out more - only to the detriment of the sound quality and reliability of the device, the latter problem for a pop amplifier is especially acute.
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The previous version of the article was written (or rather, COMPILED) in a terrible hurry. Subsequently, many forum participants noticed all sorts of absurdities, such as: the inconsistency of Ktr with the given Ra, the number of turns of the primary and secondary systems were inaccurate, etc. Having raised all my archives (not calculated, but winding ones - I have such), I clarified everything, combed his hair, made him look divine. […]
Amplifier and power supply circuits [made by I. Butin]: ^ Click to enlarge ^ ^ Click to enlarge ^ The output stage is assembled with a fixed bias, requires adjustment of the anode current in silence mode by test points-voltage drop of 0.035-0.04V DC on 1 Ohm resistors in the cathodes of the output stage lamps with bias tuning resistors in the power supply. The input stage-phase inverter is made [...]
The transformerless, single-ended tube-transistor power amplifier described in the article is a further development of the principles and approaches described in the first article, and with proper execution you will get a full-fledged Hi-End design, which in terms of musicality, quality and beauty of sound is on a par with the best examples of classical tube-transformer power amplifiers. The sound of this amplifier is distinguished by a large-scale panorama, a deep and clearly traced scene and [...]
The output power of a single-ended ULF can be increased by connecting one or more lamps in parallel to the lamp of the output stage. Thus, at the same supply and anode voltage, the anode current and, accordingly, the output power of the stage increase by a factor of two or more. An example of parallel connection of an additional lamp in the final stage of a single-ended ULF is shown in Fig. one. […]
