813 amplifier build
While the usual approach over the past twenty years or so in the design of a linear amplifier is to opt for a triode [ or triodes ] running class AB 2 in grounded grid configuration, I chose to revamp a design rarely seen these days. This is the once well known G2DAF circuit. It was quite popular with British amateurs, and to a lesser extent, with USA amateurs in the days of rigs with a vacuum tube output stage. For those not familiar with the configuration, a resistor or resistive network of - W replaces the tuned circuit of a grid fed amplifier.
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HF 813 Linear Amplifier
This is a single-ended triode amp that I built using the transmitting pentode , connected as a triode. It's a fairly powerful SE amp that works very well. It uses a single pentode as the driver a 12HG7 video amp tube , and a solid-state power supply with a microprocessor controller. This amp generates around volts, and the power supply described below can deliver a lot of current.
The result is that there is a real hazard from the voltage and energy available. Don't come looking for me if you start a fire or electrocute the cat! You've been warned Here's a schematic of the amplifier. As you can see, the amp circuit itself is simple. I made up for this simplicity in the power supply, as you'll see further down the page! The main peculiarity of the amp circuit, I guess, is the single-tube pentode driver.
They are amazing devices, capable of providing very low distortion, high gain, and low output impedance all at the same time The driver has a very nice harmonic profile, with the 3rd harmonic always below the 2nd. At lower levels, the 2nd is about the only harmonic that's measurable. For some reason pentodes seem to have the reputation for creating more high-order harmonics, but it's simply not true in a single-ended design. It also does much better than a 6C45pi-E.
I also tried these tubes triode connected with a CCS, and they did well that way - about the same as a 6C45pi did, I guess. But I preferred the pentode connection. Try it, you'll like it! The output stage is an tube, connected as a triode. It was a common tube in smaller AM broadcast transmitters, especially as a modulator. I got much encouragement, as well as triode curves for the , from Paul LeClercq.
He has posted info on the triode push-pull amps that he's built, as well as the triode mode curves for the By the way, the grid lines on the curves are at 10V increments; the first leftmost is 0V, the next V, then V, V, etc.
I operate the output stage with a plate voltage of about V, and a plate current of mA. I used fixed bias, which requires around V. I suspect 5k is probably about the lowest load you'd want to use with the Here are some measurements I made of the amp. Note that these were on the breadboard, not the final product:.
The power supply I built for the amp is a solid-state rectified supply that uses two large toroidal transformers, one for the high voltages, and one for the low voltages filament power, etc. It uses a microcontroller to sequence voltages at power-up, and monitor power supply voltages and plate current, as well as temperature.
Data is displayed on an LCD display, and if any parameter goes out of tolerance the amp is shut down and an error message is displayed. A voltage doubler is used, which produces around volts, and at the midpoint of the doubler capacitors, about V.
The driver G2 supply of V is derived from the V supply with a zener regulator. My original HV supply design was to use linear regulation. I never got the regulators to work to my satisfaction, and after blowing up a handful of power FET's, gave it up in favor of a simple RC filter.
Chokes would be better than resistors, but at this point I was pretty committed to the mechanical design, and didn't have any room for them. This is rectified to give approximately 50V DC.
The 12V supply is used for the driver filament, as well as powering miscellaneous stuff like relay coils. It's also used to power linear regulators to generate 5V and 3.
The 10V filament supply passes through a polarity reversal relay, which is energized every other time the amp is powered up the micro remembers the last state in flash memory to reverse the polarity of the DC filament voltage. This theoretically keeps one side of the filament from wearing out before the other, since the low voltage end of the filament should tend to emit more electrons than the high voltage end. The 10V filament supply is DC isolated from the input floating , and plate current is measured by placing a small sense resistor in the path to ground.
Power to the filaments is filtered by a toroidal common-mode choke, which makes the filament circuit pretty high impedance to anything over around Hz, and also serves to reduce any remaining noise form the switching DC-DC converter.
The 36V AC is also applied to a small transformer working "in reverse" secondary as primary, etc. Note the arrangement of resistors around the bias pot, which provides full bias to the tube if the pot happens to get dirty and open - gotta think about this kind of thing when you're talking about a design that can easily pump a few hundred watts into the tube before the OPT winding opens!
In order to provide sequencing of the power supply, monitoring of critical voltages, currents, and temperature, and provide a display of these things, I used a microcontroller. This is really a single-chip data acquisition system, a very nice device. If any of these items fall outside of the limits programmed into the microcontroller, the amp will shut down, and an error message will be displayed.
The micro also provides a specific power-up and power-down sequence. To power up, the filaments are heated for 30 seconds, with polarity reversed every other power-up as described above. Then, the normal monitoring loop is entered, and plate voltage and current is displayed on the LCD, alternated with the temperature inside the case. The micro displays info on a 1x16 line LCD character module. Here are some pictures of typical displays:.
If you're interested in such things, here's the assembly-language code that runs in the amp. This is code written specifically for the Cygnal CF, so it won't work exactly on other processors, but if you know 's it's not hard to port. Source and oblect code and listing 37k ZIP file.
I wired an LCD display onto the demo board, and used a bunch of pots to simulate the voltages, and developed the code on the demo board. The power supply for the amps are constructed on a PC board. The audio section, like my B amps, is built point-to-point using single-point terminals on bare copper-clad PCB material. I built the amp chassis out of MDF. I would not encourage you to do this, though - the MDF traps too much heat.
I started off by trying small fans to move air through the box, but it was too noisy. I finally went with a perforated bottom, and added air holes along the sides of the box. Even so, it gets hotter inside than I'd like. In fact, that's why I added the temperature sensor to the micro, to be able to shut down if it gets too hot in there.
This file shows most of the interior wiring, as well as all the parts. It is not dimensioned, but is drawn to scale. This view shows the inside of the chassis, with the bottom hinged open. The copper clad PCB with the parts on it is mounted on the chassis underside, held in by the tube socket screws, and the PS PCB is mounted to the bottom of the case. The bottom of the case, made out of perforated aluminum, is attached to the box with a section of continuous hinge piano hinge.
A view showing the interior wiring, pretty self-explanatory. The fat purple wire is rated for 5kV. The anode lead comes in at the right edge of the picture it's black and hard to see. The two power resistors going from the filament pins to ground provide the primary signal current path from the cathode to ground.
The AC wiring, showing the relay that controls the primary of the HV transformer coil isn't wired yet. You can see MOV's metal oxide varistors, the red discs and inrush limiters the black discs were used on each transformer primary. The squares with finned heatsinks are the 5V quarter-brick DC-DC converters, wired in series to supply the filament. The black heatsinks are used with TO power resistors part of the RC filtering.
The small transformer in the upper right is for the bias supply. The bare PCB material with single-point terminals before installation and wiring. The big hole is for the socket, the small one for the 12HG7 socket, which are mounted to the chassis after the terminal board actually, the screws hold the terminal board in. Note the common mode choke installed in the board before assembly to hide the screw head.
Some assorted single-point terminals. This is what's under the aluminum can: two Plitron toroidal transformers. In case you're wondering if it's OK to stack two toroids this way, I cleared it with the Plitron engineer - he told me that there are no magnetic issues, the only thing to worry about is heat buildup. This design is so conservative that the transformers don't even get warm to the touch, so we're OK here. So, you wanna build an SE amp As in all projects, I learned a few things building this amp that I should share with any potential builders out there.
First of all, be VERY careful with a high-voltage, low-impedance power supply like this. Subtle things can bite you. For example, if you look at the schematic you'll see some resistors in series with the HV secondary coming onto the PS board. These serve to help filter rectifier noise from getting out to the transformer. I initially had metal film resistors in series-parallel there, plenty of margin for the RMS power.
But on about the third power-up cycle, I heard a most impressive sound as the metal film vaporized and created a nice plasma arc that persisted for a second or two. Moral of the story: you MUST use a resistor like a carbon composition in an application where there are large peak powers to be dissipated. Metal film doesn't work. You'll also notice lots of resistors stacked in series in several spots.
This is because when you're talking about V or so, you have to worry about the voltage ratings of resistors, not just the power.
HF Tube Amplifiers
The AD is a low power, single supply triple video amplifier. Each of the three current feedback amplifiers has 50 mA of output current, and is optimized for driving one back terminated video load W. The AD features gain flatness of 0. This makes the AD ideal for broadcast and consumer video electronics. The AD offers low power of 5.
Aries Cerat
When you subscribe, you receive only messages for the product you have subscribed to. You can check your current subscriptions and remove yourself from subscriptions at any time by visiting the Reviews Home page and clicking on the 'here' box under Subscriptions. If you have comments, questions, or problems with this procedure please write to the Forums Manager. This project involves a management team of volunteers who each take a topic of interest and manage it with passion. The site will be something of which everyone involved can be proud to say they were a part. Toggle navigation. Forgot Password. Reviews Home. Running anode color comparisons with a Cetron B several decades ago I estimate the actual plate dissipation to be around W for the graphite version which makes the 4 I built a solid W amp for CW and SSB.
813 Homebrew Amp with Power Supply from recycled parts.
An Amplifier by Paul Leclercq. This article concerns push-pull amplification and may, therefore, cause distress to certain sections of the readership. It has to be said: it's fascinating reading accounts of individuals designing and building valve amplifiers. I'm sure they do it properly. You know the sort of thing: days of calculus and other brain-torturing processes, followed by careful drawings etc.
Welcome to Steve's Vacuum Tube Related Web Site
This document is a design note compiled during the design and construction of a linear amplifier. It is intended as a catalogue of ideas and thoughts to be shared. Some of the design ideas worked well, others failed miserably, but that is the nature of homebrew. This is not a construction project. If you really need or want a linear amplifier, then go out and buy a commercial product.
813 Tube Amplifier Schematic
The Navy decided to dump two old 10KW AM beacon transmitters into the ocean and replace them with modern units. I convinced the communications officer to allow me three days to pull parts off these transmitters before they dumped them and from these parts I built a A linear amplifier. I used that amplifier for nearly thirty years in various locations until the HV transformer shorted to ground and then I gave most of it to someone who really wanted a linear and had the parts and talent to replace the HV system. I am neither an engineer nor technically trained so my electronics knowledge is self-obtained and has lots of holes in it. I have a third with a steel plate and might do something with that later. A watt is a watt.
813 Linear Amplifier
To get more information contact me at: webmaster audiodesignguide. This is an expert-only project because the high power supply voltage, about 1KV. Be careful, it can kill you! Keep always one hand better if it is the left hand behind your back.
The Genus SET integrated amplifier is the answer to the challenge of making them smallest possible one-box integrated amplifier which would carry our design philosophy. With a footprint of mm x mm it is our most compact design to date, yet remains faithful to our no compromise approach. The Genus integrated is 25W in Class A1 yet only has two gain stages. It takes key design ideas from our Concero 25 monoblock circuit. This single tube stage offers maximum linearity and bandwidth for maximum transparency.
QRZ Forums. With all the emphases on commercially manufactured gear. I was wondering how many people are running homebrew 's. With all the Technician upgrading and considering how cheap these tubes are you would think there would be a lot of interest. If I remember correctly a single is good for about PEP. I guess I will be the first to confess, I have a nice homebrew amp running two 's. I was even thinking of building another one.
The is a good general purpose beam power tetrode and used to be popular with amateurs in the old days as a power amp valve. Building a large power amplifier is really two projects in one, the power supply and the amp itself. First up is the power supply.
Matchless topic, very much it is pleasant to me))))
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Thank you for this information, but I dare to add some criticism, it seems to me that the author overdid it with the presentation of the facts, and the article turned out to be rather academic and dry.