They say that everyone dreams of becoming an astronaut in childhood. Almost the same - to make an amplifier on the G-811 tube (811A in the Western way) is the dream of every tube lamp. Why? They say that it gives an extraordinary live sound. I have already made several attempts to approach this lamp - look and But, as often happens with the dream of becoming an astronaut, so far it has remained only a dream. Before you is another attempt.

What makes this lamp so special? There are several points that greatly complicate the creation of the ULF on the G-811. Probably - this is the high internal resistance and the pentode nature of the I - V characteristic - this creates additional difficulties in the design of the output transformer. But the most unpleasant thing is that the lamp is "left-handed", that is, it works in the area of ​​the grid currents - and this creates additional difficulties with swinging. Well, and the last one is the high Miller capacitance, which is due to the high mu of this lamp - all this together significantly increases the requirements for the driver.
Of course, a lot of amplifiers on this tube have already been made before us. However, there are few happy owners of ready-made devices. Ready-made amplifiers are quite expensive - for example, the famous WAVAC - http://www.enjoythemusic.com/magazine/equipment/0900/md811.htm, or for example the famous Shishido circuit http://lagarto-ex-infoseek.jp/shishido/shishido- skema.htm. Even more attempts to cope with this lamp have been made among diyers - http://sarris.info/main/811a-single-ended-triode-power-amp, or there is a branch on this lamp on diyaudio.ru http: // www. diyaudio.ru/forum/index.php?topic=376.60 and this one http://www.diyaudio.ru/forum/index.php?topic=2748.0

One of the points mentioned - grid currents - distinguishes the G-811 from most other lamps. Therefore, it is logical to put forward a hypothesis that it is the current nature of the control that makes the sound full and very natural. Therefore, now I set myself the task of making the entire amplifier path with the control of each stage by current with direct or transformer coupling between the stages. So far, this task has not been 100% solved, but there is not much left - to organize an input without a capacitor. The layout of this circuit already sounds:

But first about the details and parameters of the circuit. Interstage transformer - from Audioinstrument based on TW10, primary 5K, secondary 1K. Such a decrease is important for “pumping” the Miller's capacity, 6E5P in this case sees a five times smaller input capacity of the G-811. The output transformer is from the same company, TWB50, with Ra 5.3K into 8 Ohms, its primary inductance is 62 Henry (measured at 50Hz, 5 volts RMS). At the 6E5P cathode - 6 volts, on the grid - 2 volts, the 6E5P anode current - 15 mA. Frequency response - not yet fantastic - by minus three dB from 15 Hz to 26 KHz, and the upper limitation gives the output stage. The input impedance of the first stage is about 30 KΩ. The power supply is a two-story ultrafast, the mains transformer contains two 230 volt windings. Power supply 16 volts - from LM-ki. We managed to squeeze out the maximum 15 watts at 8 ohms, the first watt is very clean - minus 40 dB the second harmonic, the rest are noticeably lower than minus 60 dB. Amplifier sensitivity - 0.45 volts at the input provides 1 watt at the output (2.83 Volts at 8 ohms). G-811 mode - anode current 77 mA, power dissipated by the anode - 45 watts. Harmonic spectrum pictures are loaded. Load line:


From the load line we find that the maximum amplitude of the input voltage of the G-811 is 20 / 1.4 = 14.3 V RMS. Also, from the I - V characteristic, you can calculate the approximate value of Ri at the operating point - this is 28 kilo-ohms. Not a little, however! This is what the high inductance of the primary of the output transformer is for.
Why was 6E5P chosen for swinging? This lamp has a lot of advantages, the main of which is excellent sounding, I had the opportunity to see this in my projects on the 2A3 lamp. Well, from physics I will mention the low internal resistance Ri in the triode - 1200 Ohm with a relatively high gain - in this stage K = 29 in voltage.

The sound of the model in mono version was very pleasing, I listened to it on the speaker from the Symphony. It is very full, velvety, there is something from the pentodes of old radios, especially the middle - I really liked the vocals. The sound is also detailed like the 2A3. And, unlike the 2A3 - with a smooth, balanced and deep bass. The top is a little betrayed by the presence of germanium in the path - there is a characteristic "silver", but in general it seemed to me that this does not spoil the sound, but even quite the opposite. If in a purely transistor timbre it sticks out and soon starts to get bored, then here it complements the overall rich sound and very soon I stopped noticing it. I listened to Tchaikovsky's ballet music and a German test-CD - two hours in total and could not stop myself.
Then I decided to put together a stereo layout for revision. Inspired, in short.

In a single-ended amplifier on the 811th, you can make a 15 W amplifier per channel with a 20 Hz 80 kHz bandwidth and low distortion and output impedance< 0.4 Ом. Но это не радиолюбительская работа.

PS And the bulbs are good, probably with tungsten anodes.

The lamp is funny - a triode with a pentode characteristic,
far right, with incredible gain.
Get ready to work with grid currents (A2): read theory on interstage trans or cathode follower for swinging.

Schemes on: //www.metaleater.narod.ru/s_se.html

my experiments with this lamp, and with A2 in general,
convinced of the promise of such a path - the sound is very strong, dense, "meaty".
I took the RCA circuit as a basis, but converted it into a single-cycle one: 6E5P + 2A3 + interstage.

And at first he trained on 6N1P "enhanced SRPP" +
6P7S (in triode) - sound, compared to conventional SRPP,
became "meaty", the power increased (of course, a slight increase in the amplification of the cascade also affected). Professional musicians were thrilled to listen to (classical).
Among the shortcomings - some confusion on very heavy music (bands like “Throne of Chaos”, “Your Shapeless beauty”). In addition, 6Н1П-ЕВ worked with serious
exceeding the nominal parameters - they were enough for
six months.

Most experts advise against contacting, but
I was intrigued by N. Shishido's scheme - if he decided to do it on 811, then it is not without reason!
Toropkin

> Has anyone made an amp on such a lamp

> how does it sound

> load resistance

It only depends on you.
Anton

At 3: it will not be enough! 10-12 kΩ

the lamp is eerily right at 700 volts at the anode and 0 on the grid the lamp is locked. starts to open at + 20-35 volts on the grid. I do not remember exactly.
But probably at 3000 at the anode it behaves differently.

Used in class C telegraph transmitters.

In sound, her project will be at the level of um 70 at a weaker price.

>>> I had always heard that the Svetlana 811A "s were the most rugged of them

>> Rumor has it that Svetlana is dropping production of the 811A due to low

>> sales, Charles.

>> - Rich ..., 805.386.3734, www.vcnet.com/measures.

Charles, I would not be surprised if it "s Svetlana. Ameritron uses
811s "in both of there 811 amps. The only other 811 amp that I know of
is made by Ten-Tec and I "m not quite sure what tube they use. Cetron
BTW, also makes a good 811, but Svetlana is probably the best, high
gain, good fit and finish. Quality workmanship and tolerances. 73 "s de
Phil W2GE

Svetlana also ....... in the Ten-Tec Model 411 Centaur.

73 de Mike, W9WIS

I'm here again with the stupid idea of ​​the first (in the corrector) to put the G811 with an offset of -3V and anode 1300-140 0V. The throttle is in the load. Gain is about 150. Difficulties are above the roof, but the lamp in this mode sounds great. If you are interested, you can try joint efforts to develop such a cascade.
And the sound of a light bulb without grid currents is just wonderful!
Rezvoy

I would say for all similar straight wires with a tungsten cathode
Vasyanin

And what are our realities? Take 811 Marshall, with ribbed anodes for horizontal, $ 100 matched square, and enjoy life ...
KAA

Why "even though"? .. Ideal (or close to) current distribution in the triode, when the electric field lines inside the electrode system are most straightforward and the input characteristic is as close as possible to a straight line, in principle, is achievable only in the mode with grid currents. ..
KAA

I tried this scheme (I took it out of my head; just in case - I do not claim authorship):
Two sources. The first is 190V, better stabilized. 800 V, a usual one, is sequentially attached to it. Therefore, only kilovolts. From the plus of a large source down: wire, primary of the output trance, anode 811. Cathode 811 (through an artificial midpoint) is connected to the 6P9 anode. The 811th grid is connected to the + 190V source, the 2nd grid 6P9 sits there.
1st grid 6P9 at the entrance, at the RC cathode. R is selected so that the current through both lamps (and they are connected in series) is 40-45 mA. At the 6P9 anode, about 200V is obtained.
That's the whole scheme. Sensitivity 1 ... 1.5V, depending on the specimens. 5-6 watts easily, with 1-2% distortion. A very favorable spectrum (2-3 harmonics and, perhaps, everything). With a class 34 lamp, measurements are better, but the sensitivity is very low (a high source here should be 600 volts, a current under 70 mA). The sound is quite decent (clearly better than the 811 powered by a cathode). The advantage of the scheme is its extreme simplicity. The downside is the need for a good weekend trance with a reduction of 8-10 kOhm (the random copy I had played, strictly speaking, more than the middle). And one more minus - a very large "plus" on the anode sticking up. Fearfully...
Evlampy

Message from Alexey Shalin

> But there is also such a moment: the non-sprayable getter with its "visible absence" often

> cheats newbies into rejecting quite good lamps

I agree, the G-811 has a non-sprayable getter, you can immediately see the ring on the anode. But you need to know this.
shi

I agree with Eugene about 572 \ 811. Indeed, after (according to my observations) 600 ... 650V they give a somewhat simplified sound, which, in general, has its physical justification - the overall dimensions of the anode and the geometry of the electrode system are such that the edge effects at the grid-anode field strength above 1.5 ... 2 MV / m are strong enough and lead to the formation of "virtual" triodes with high permeability from the bottom and top of the anode. In GM70, the interelectrode distances are larger and similar effects take place at much higher voltages. From this point of view, 350 ... 400V for 811/572 approximately correspond to 1.2 ... 1.5kV for GM70.
Lynx

One time ago I listened to CE on 811, the mode is such that it does not climb out of positive displacements on the grid at all, swinging with a pentode through a powerful (on 6L6) cathode follower. Great, fast, detailed sound! With all my prejudice against both 811 and A2, and against a lot of other things in this device! But - the soup is voting "for"!
HRYUN

The G811 lamp looks like the widespread G807 beam tetrode, although it is a bit larger. But the G811 is a completely different lamp. Worse or better? This is a rhetorical question. But the fact remains that this is a directly heated triode. There are many different fabrications regarding the direct heating of the network, justifying the special sound quality. And in fact, direct heat has no objective advantages over indirect. The opposite is true. Since it is necessary to use a galvanic isolation of the filament circuits, this is reflected in the weight and dimensions of the entire structure.

An example of a tube amplifier circuit is shown in the figure below. Given the good controllability of the triode, a simple implementation with one lamp in the preamplifier unit can be used to build a push-pull circuit. You can start right away with the bass reflex. Or you can apply Williamson's scheme. Who likes what. The main thing is to provide decoupling from the filament circuits of the output lamps and to make autonomous sources of symmetrical supply voltage, directly on the alternating current of the industrial frequency. The fillers will have to be wound, and you will need 4 toroids of 25 watts or a pair of toroids of 50 watts, respectively. There is no standard solution here and you will have to use assault. The wires from the filament transformers are high-current, so they must be laid with twisted pair at a short distance directly from the toroidal filament transformers located in the basement. Crossings with signal wires should be avoided.

Since the anode voltages of the G811 output lamps are relatively high, the supply voltages of the anodes of the preliminary stage should be limited. It's a good idea to use a parametric stabilizer for this. A stable voltage will significantly improve the operation of the phase-inverted stage. And since the intrinsic consumption of the small double triode anodes is small, the stability will be extremely high. It is convenient to use a differential pair designed for low currents and high voltage as output transformers. Output lamps have permissible cathode currents of no more than 150 mA. Therefore, you can't run away much here. A pair of matching transformers in the size of about 60-80 watts will be quite sufficient.

Triodes G811 are pretty pretty appearance... Their number is limited. But they can be bought here in proven pairs, at a price 25% lower than in Istok. Tube amplifier on such beauties here you can also buy on a prepaid basis. But it will cost quite a lot, from 100K and more. To purchase, it is enough to contact me by mail, discuss the price and terms of delivery, self-pickup is possible. After that, those who wish should call the phone number indicated on the website to discuss the details, and only then make an advance payment of 20% of the contractual amount to my account with the Savings Bank. Having received the transfer, I send a notification and within two weeks I will call back myself with confirmation of the proper packaging of the product and readiness for shipment, and I will send photos of this particular unit, open and packed, to the mail. For shipment, the buyer is obliged to transfer the remaining amount, after receiving which I carry out the shipment and mail a copy of the receipt. If the circumstances of the buyer have changed in the specified period of time, then the purchase can be canceled. The listed deposit is not refundable. The amplifier is guaranteed for 12 months from the date of delivery. The warranty does not apply to glass in the conditions of postage and transportation by a transport company. Sincere wishes for good health and success to all.

Evgeny Bortnik, Krasnoyarsk, Russia, November 2017

The linear amplifier for the transmitter of a category I radio station is designed for linear amplification of single-sideband, telegraph and AM signals in the ranges of 10 ... 80 m. when pronouncing a long “a” in front of the microphone) is also 200 W, while the peak power input can reach 400-500 W. The amplifier efficiency is 65-70% depending on the operating range.

The amplifier uses four parallel-connected G811 lamps according to the scheme with the OS. The total power dissipation at the anodes is 160 W, so it is possible to carry out fairly long sessions of tuning the transmitter with an input power of 200 W.

Due to the low output capacitance of the G811 lamp (6 ... 7 pF), several lamps can be switched on in parallel. In this case, the anode current increases in proportion to the number of lamps, which is equivalent to using a lamp with a large anode current pulse at a not very high anode voltage (1000 V). The resistance of the anode load is low. This, along with the low output capacity of the G811 lamps, contributes to the high efficiency of the amplifier in the ranges of 10 ... 15 m, where it is difficult to create a circuit with a large equivalent resistance and high efficiency.

The similar impedance of the amplifier depends on the number of lamps connected in parallel. With four lamps, it is equal to 75 ohms.

When receiving signals, the amplifier tubes are locked with a voltage of -27 V supplied to the grids through the winding of the antenna relay K1. The contacts of this relay connect the antenna to the X3 socket, where the receiver input is connected. When transmitting signals, the grids of lamps are connected to the transmitter body by switch S1 or to an external contact (for example, in a transceiver) through socket X5. In this case, the K1 relay is triggered and connects the antenna to the transmitter output. A tuning indicator is connected to the amplifier output, the sensitivity of which is regulated by the resistor R6.

The choke L9 in the heating circuit is wound simultaneously with three wires on a ferrite rod with a diameter of 12 mm and a length of 140 mm made of F-600 material. The number of turns is 40. The diameter of the extreme wires of the inductor through which the filament current passes is 1.5 mm, the diameter of the middle wire, which passes the cathode current, is 0.51 mm. The T1 filament transformer provides a voltage of 2 X 6.5 V at a current of 8 A. Its overall power is 110 W. Coils L1 ... L4, wound on resistors RI ... R4 of MLT-2 type, contain 5 turns of PEV-2 wire with a diameter of 0.62 mm. Anode choke L6 is wound with PELSHO-0.35 wire on a porcelain frame with a diameter of. 20-25 mm and 150 mm high. The number of turns is 150, 50 turns closest to the anode are wound with a pitch of 0.5 mm. Chokes L7 and L8 of any type.

At the output of the amplifier, a P-circuit is used. Capacitor C12 must have a plate gap of at least 1.2 mm. Capacitor C13 is a triple unit of variable capacitors from an old-style radio receiver (with a gap between the plates of at least 0.3 mm). The rotating coil L5 is wound with a wire with a diameter of 2 mm and is equipped with a turn counter. Since the output P-circuit has three adjustable elements, for the correct tuning of the amplifier in the range of 80 m, it is necessary to set the maximum capacitance of the capacitor C12 (250 pF); when operating on a coaxial feeder and low VSWR, the capacitance of the C1 capacitor should also be close to the maximum. The circuit is tuned into resonance by rotating the coil L5, the connection with the load is controlled by the capacitor C13. In the range of 40 m, the capacitance of the C12 capacitor is 120 pF, in the range of 20 m-50 pF, in the range of 15 m it should be close to the minimum, in the range of 10 m it should be minimal.

When installing the amplifier, the input circuits must be separated from the output circuits, for example, the input circuits must be placed under the chassis, and the anode circuit parts must be placed above the chassis. HF conductors should be as straight and short as possible.

A properly assembled amplifier starts working immediately. With self-excitation, the resistance of the resistors R1..R4 should be reduced by 1.5-2 times. When amplifying a single sideband signal, an excitation power of 25 W is required to achieve an anode current of 400 mA at the peak envelope.

G811 lamps can be replaced with GU50 lamps in triode connection. To maintain the same input resistance (75 Ohm), three GU50 lamps are connected in parallel. Since the GU50 lamp has a heated cathode, excitation must be applied to the cathode. The middle wire of the filament choke is connected to the cathode.

S. Bunin, L. Yaylenko
"Handbook of shortwave radio amateurs"
Linear amplifier on G-811

The linear amplifier for a radio station of the 1st category is intended for linear amplification of single-sideband, telegraph and AM signals in the ranges of 10 ... 80 m. When amplifying telegraph and single-sideband signals, the average input power is 200 W, while the peak power can reach 500 W.

The amplifier efficiency is 65-70% depending on the operating range.

The amplifier uses four parallel-connected G811 lamps according to the scheme with a common grid. The total power dissipation at the anodes is 160 W; therefore, rather long sessions of tuning the transmitter with an input power of 200 W can be carried out. Due to the low output capacity of the G811 lamp (6 ... 7pf), several lamps can be switched on in parallel. In this case, the anode current increases in proportion to the number of lamps, which is equivalent to using a lamp with a large anode current pulse at a not very high anode voltage (1000 V).

The resistance of the anode load is low. The input impedance of the amplifier depends on the number of parallel-connected lamps. With four lamps, it is equal to 75 0m.

When receiving, the amplifier tubes are locked with a voltage of -27 V supplied to the grids through the winding of the antenna relay K 1. The contacts of this relay connect the antenna to socket X3, where the input of the receiver is connected. When transmitting, the grids of lamps are connected to the transmitter body by switch S1 or to an external contact (for example, in a transceiver) through socket X5. In this case, the K1 relay is triggered and connects the antenna to the transmitter output. A tuning indicator is connected to the amplifier output, the sensitivity of which is regulated by the resistor R6. ...

The choke L9 in the heating circuit is wound simultaneously with three wires on a ferrite rod with a diameter of 12 mm and a length of 140 mm made of F-600 material. The number of turns is 40. The diameter of the outermost wires of the inductor through which the filament current passes is 1.5 mm, the diameter of the middle wire passing the cathode current is 0.5 mm.

The filament transformer T1 provides a voltage of 2x6.5 V at a current of 8 A. Its overall power is 110 W.

Coils L1 ... L4, wound on resistors R1 ... R4 of MLT-2 type, contain 5 turns of PEV-2 wire with a diameter of 0.62 mm.

Anode choke L6 is wound with PELSHO-0.35 wire on a porcelain frame with a diameter of 20-25 mm and a height of 150 mm. The number of turns is 150, the 50 turns closest to the anode are wound with a pitch of 0.5 mm.

Chokes L7 and L8 of any type.

At the output of the amplifier, a P-circuit is used. Capacitor C12 must have a plate gap of at least 1.2 mm. Capacitor C13 is a triple unit of variable capacitors from an old-style radio receiver (with a gap between the plates of at least 0.3 mm). The rotating coil L5 is wound with a wire with a diameter of 2 mm and is equipped with a turn counter. Since the output P-circuit has three adjustable elements, for correct setting amplifier in the range of 80 m must be installed maximum capacity capacitor C12 (250 pF) when operating on a coaxial feeder and low VSWR, the capacitance of capacitor C13 should also be close to the maximum. The circuit is tuned into resonance by rotating the coil L5, the connection with the load is controlled by the capacitor C13. In the range of 40 m, the capacitance of the C12 capacitor is 120 pF, in the range of 20 m - 50 pF, in the range of 15 m it should be close to the minimum, in the range of 10 m - the minimum.

When installing the amplifier, the input circuits must be separated from the output by a screen, for example, the input circuits should be placed under the chassis, and the anode circuit parts above the chassis. HF conductors should be as straight and short as possible.

A properly assembled amplifier starts working immediately. With self-excitation, the resistance of the resistors R1 ... R4 should be reduced by 1.5-2 times. When amplifying a single sideband signal, an excitation power of 25 W is required to achieve an anode current of 400 mA at the peak envelope.

G811 lamps can be replaced with GU50 lamps in triode connection. To maintain the same input resistance (75 0m), three GU 50 lamps are switched on in parallel. Since the GU50 lamp has a heated cathode, it must be energized to the cathode. The middle wire of the filament choke is connected to the cathode. The amplifier is assembled in a metal box 200 mm high, 400 mm wide and 300 mm deep. The power supply unit of the amplifier can also be placed in the same box. A small exhaust fan is installed inside the amplifier to lower the temperature.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Sergei Safonov (4Z5JK)
KV-journal No. 5-97
Transformerless power supply of RA on G-811

Modern small-sized high-capacity electrolytic capacitors for flash photography allow the design of transformerless high-voltage power supplies for tube output stages of power amplifiers.
A schematic diagram of one of such sources, providing a voltage of 1200 V - for powering the anode circuits of a power amplifier on four G-811 lamps, is shown in the figure.

The rectifier is made according to a full-wave circuit with voltage multiplication by four times. The use of full-wave voltage multipliers improves the load characteristic of power supplies and reduces the ripple of the rectified voltage.
A distinctive feature of the amplifying cascades, powered by a transformerless circuit, is the absence of a galvanic connection of the lamp electrodes with the body and, therefore, the absence of a galvanic connection between the body and the mains.
To prevent "tingling" from the equipment case through the blocking capacities connecting the case to the network, as well as for the purpose of general electrical safety, the equipment must be reliably grounded.
The likelihood of self-excitation of amplifiers in the low-frequency ranges is reduced by the use of two blocking capacitors in the anodes and cathodes of lamps, one non-inductive with a capacity of 0.01 μF (KSO, SGM, etc.), the other - paper with a capacity of 1 ... 2 μF with an operating voltage of at least 600 V. For the same purpose, additional filter chokes with an inductance of about 500 μH with a small turn-to-turn capacitance are installed in the anode circuits. You can use ready-made chokes on ferrite magnetic circuits.
To prevent diode failure, the mains voltage is applied in two stages. When the amplifier is connected to the network, the voltage to the rectifier is supplied through a limiting resistor. After a few seconds, the latter is short-circuited using a button and a self-locking relay.
With the values ​​indicated on the diagram electrolytic capacitors in the power supply and load current of 600mA, the output voltage drop is about 10V.
The above-described transformerless power supply has been successfully operated in the author's KB equipment for several years and has established itself as a reliable device.

"KV and VHF" 11-96.
Power amplifier on a lamp 811-A (G-811)

One of the variants of the 811-A power amplifier was presented by the ARRL technical laboratory.

When repeating, you can use an analogue of 811-A - the domestic G811 lamp.

Technical data:
Rin --- 50 Ohm;
Rout --- 50 Ohm;
Work class --- B2;
Рвх --- 12 ... 15 W;
Rpodv. (to the anode) --- 200 W.

The lamp is switched on according to the scheme with a common grid and the input resistance at the cathode VL1 is about 300 ohms, therefore, in order to obtain Rin = 50 ohms, input circuits are used.

The amplifier uses the following parts:
S1 - ceramic base switch.
L1 -5 ... 9 μH;
L2 - 3 ... 5 μH;
L3 - 1.6 μH;
L4 - 1 μH;
L5- 0.4 ... .0.8 μH.

The coils of the input circuits are wound on frames with SCR cores.

Dr1 is an incandescent choke, wound on a round ferrite rod with a diameter of 8 mm with a permeability of 400 ... 600 with a PEV wire of 1.6 mm and contains 30 turns in two wires. To increase the quality factor of the choke, a step of about 2 mm should be maintained between each pair of winding turns. Before winding, the ferrite is wrapped in two layers of varnished cloth.

Dr2 - frameless, 4 turns of bare copper wire 1.6 mm, diameter - 17 mm, length - 30 mm. Resistor R3 is located inside the winding. As the latter, two 100 Ohm, 2 W resistors are used, connected in parallel.

L6 - 22 turns with 2 mm bare copper wire on a 50 mm frame. Taps - from 2, 3, 5, 10 turns, respectively, counting from the variable capacitor C10.

S2 is a ceramic base switch.

P1 - measuring head 0 ... 1 mA. Both the anode current and the grid current are monitored.

VD1, VD2 - diodes 200 V, 750 mA.

VD3 ... VD8 - power diodes 600 V, 500 mA.

The high voltage winding T1 is rated for 400 mA at 540 V.

С14, С15-electrolytic capacitors 10 microns, 25 V.

The input circuits are tuned with cores at the full anode voltage of the amplifier and an excitation power of 12 ... 15 W at a minimum SWR between TX and the amplifier input.

The amplifier operates in class B2, so the occurrence of grid current should not be a concern. When the latter appears at the time of tuning the P-circuit, it is necessary to ensure the outflow of power to the load using C10 and C12. The amplifier is calibrated using an RF-voltmeter and a 50 Ohm antenna equivalent, determining the power delivered to the load.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Here is another version of the UM on the G811:

Lamps with the right characteristic G-811 work well with zero bias on the grid, and therefore there is no need for a bias voltage source. The anode current of the G-811 lamp with an SSB signal amplification can reach a fairly large value, up to 210 mA. When several lamps are connected in parallel, the anode current increases in proportion to the number of lamps, which is equivalent to using a lamp with a large anode current pulse at a not very high anode voltage (1500 V). Such a lamp is known to require a small equivalent anode load resistance. This, along with the low output capacity of the G-811 lamps, is very convenient when working on the ranges of 10-15 m, where it is rather difficult to create a circuit with a large equivalent resistance. The input resistance in the circuit with a grounded grid for two G-811 lamps is approximately 150 ohms, for four - 75 ohms. This makes it possible to apply the appropriate coaxial cable to supply excitation to the amplifier.
The picture above shows the circuit linear amplifier on two lamps G-811. The designs of most of the circuit elements have been described earlier. There are no particular problems with the tuning of the amplifier.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Matching Transceiver and Power Amplifier
on the example of an amplifier on 4 G-811

When connecting imported transceivers with broadband transistor amplifiers power to homemade tube output stages, on different ranges other than 50 Ohm, I recommend using switchable P-circuits.
The table summarizes the parameters of the P-circuits for all short-wave radio amateur bands and gives the input impedance of the output stage, assembled according to a scheme with common grids on 4 G-811 lamps.
The power amplifier has the following parameters:

Ua = 1320 V.
Io = 60 mA.
Pin.vax = 35 W.
Pout. = 540 W at Rheat. = 51 ohms.

In order to increase the reactive power, each of the P-circuit capacitors C1 and C2 consists of two constant capacitors for an operating voltage of 250 ... 500 V. The input capacitance is about 25 pF. The length of the connecting cable between the transceiver and the PA = 45 cm. The capacitance values ​​given in the table are indicated taking into account the input capacitance Svh and the capacitance of the connecting cable.
The U-loop coils are wound turn-by-turn on cored frames for fine tuning. Frame diameter 10 mm.

Range, m ._______ Rin, Ohm ______ Number of turns ___ Wire diameter, mm ___________ C1, pf ________ C2, pf

160________________94,6____________25_____________0,51_____________________1500__________1220
80_____ ___________ 69,3____________14_____________0,51_____________________1220__________1020
40_________________47,4_____________8_____________0,51_____________________1000__________1000
30_________________43,4_____________6_____________0,81______________________720___________780
20_________________44,6_____________5_____________1,3_______________________460___________510
17_________________27,6____________4,5____________ 1,3______________________360____________460
15_________________21,1_____________4_____________1,3______________________ 320____________400
12_________________16______________3,5____________1,3______________________ 290____________380
10_________________11,4_____________3_____________1,3______________________ 266____________350