Hf amplifier power supply
Amateur Radio Stack Exchange is a question and answer site for amateur radio enthusiasts. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. My intent with the amp is that it plays a central part in this design that i am working on. Power will be delivered via separate power source. The applications will be bountiful, currently, I am in the design phase, I cannot yet be able to operate.
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Vintage Galaxy 200 Ham Radio Amplifier / Power Supply
Having searched the Web for reference material and found very little! Power supplies are needed for every type of amplifier or any other electronic equipment for that matter we will ever use. I do not intend to deal with 'esoteric' designs with interesting names, but the simple, unregulated linear power supply that is still the mainstay of audio power amplifiers. This specifically excludes switchmode supplies, which are a great deal more complex.
These linear supplies should not create any problems for anyone, because they are so simple, right? They appear simple, but there are many inter-related factors that should be considered before just embarking on your next masterpiece.
The purpose of this article is to explain the terminology used, traps and pitfalls, and give some insight by way of a few practical examples.
Most of the general principles described can be translated to higher or lower voltage or current with no change to the basic parameters. If the voltage is increased, you simply need to ensure the diodes are rated for the worst case PIV peak inverse voltage to which they will be subjected. This depends on the type of rectifier used, and is described in more detail further below. One omission that will be apparent to many readers is any reference to valve vacuum tube rectifiers. Contrary to the firmly held beliefs of some, they have exactly zero sonic benefit in any design, but there are people who for reasons that I can't determine prefer the power supply to sag under heavy load.
This is replicated easily by using resistors in series with silicon diodes, of a value similar to that found in the valve data sheet.
For example, a 5AR4 has a typical plate resistance of around 50 ohms at 25mA plate current, and a silicon diode in series with a 50 ohm resistor will give virtually identical results.
All valve rectifiers also impose an upper limit on the capacitance following the rectifier, and that usually means that the filter cap is far too small to provide acceptable filtering. Valve rectifiers have one and only one redeeming feature - they provide a 'soft start' as the filaments or heaters warm up. Anyone who claims to be able to hear the difference between a valve and silicon diode rectifier is either suffering from wishful thinking or self-delusion.
As always, any test must be double-blind or the 'results' obtained aren't worth the time spent obtaining them. You also won't find anything here that suggests or recommends ultra-fast or fast recovery diodes, because there's simply no point for 50Hz or 60Hz mains. However, as noted in section 9, they don't do any harm and if that's what you prefer then use them by all means.
Fast diodes essential in switchmode supplies because they operate at anything from 25kHz up to kHz or more. They don't 'sound better' than ordinary diodes, and again, only double-blind tests will reveal if anyone can really hear the difference.
Remember that the idea of a rectifier and filter is to produce DC which is then used by the electronics. The idea that one rectifier type supposedly sounds 'better' than another is quite silly. There is no evidence that there is the slightest difference to sound quality if fast diodes are used, despite countless unsubstantiated claims. In some cases you may get a small reduction in conducted emissions high-frequency interference sent back into the mains wiring.
For anyone who would like to run transformer power supply simulations, I suggest you read the article Power Supply Simulation Not As Easy As It Looks , which covers the tricks you can use to make a simulator emulate the 'real world' performance of transformers and rectifiers.
It's important to understand that the so-called 'linear' power supply is not linear at all. Current is delivered from the transformer and the mains only when the AC voltage is greater than the stored charge in the filter capacitors. The waveform is highly non-linear and can inject noise into any wiring that's close by including speaker cables!
Mains and other AC wiring should be kept well separated from all signal and speaker wiring. The 'ground' point must always be taken from the centre-tap of the filter capacitors for a split supply to prevent diode switching noise from being injected into the ground wiring.
Never take the ground from the transformer centre-tap, even if there's only a few millimetres of wire between that and the filter caps. Likewise, DC must be taken from the filter caps, and not from the bridge rectifier.
You need to be aware that transformer secondary voltages are nearly always specified at full rated current into a resistive load. With a resistive load, the regulation is around This is completely normal, and it happens with all transformers. As a result, all linear power supplies will provide more than the expected voltage with no or light load, and less than expected at full load. Failure to appreciate this is common, largely because most articles that describe linear power supplies either don't mention it, or it's glossed over expecting that "Everyone knows this".
In reality, everyone does not know this, other than from their own measurements, which may or may not be sufficiently accurate. Mains voltages are nominally V or V, but the actual voltage varies from hour to hour and sometimes minute to minute.
If the input primary voltage changes, so too does the secondary voltage, in direct proportion. That's only one of the many reasons that your DC voltages are different from the theoretical values. We expect a sinewave from the mains, but it not - it's invariably distorted. The degree of distortion varies throughout the day, and depends on the current loading on the grid. Section 5. Surprisingly perhaps perhaps??? Provided you understand that the results are very approximate, then you're well on your way to understanding linear power supplies.
Power supplies themselves require several definitions these are discussed later in this article , but the requirements of the amplifier that is to be connected need to be understood before we start. This makes a very big difference to the way the supply performs. Poor earthing practices, such as connecting components to the nearest available ground reference can and do also create problems, and these can introduce hum, or more usually a 'buzz' into the signal circuits.
This applies equally to Class-AB and Class-A amplifiers, but is usually more apparent with Class-A since the maximum current is drawn on a continuous basis. Transformer leakage flux can also cause buzz, so ensure that DC, speaker and signal wiring is kept well clear of any transformer. Toroids have lower leakage flux than E-I transformers, but they can and do still cause problems.
Because a transformer's flux density is highest at no or light load, any mechanical noise will be greatest at idle and with low audio levels, and this is exactly where people expect their equipment to be noise-free. Any amp that draws a quiescent current through the output devices is by definition, Class-AB.
For true Class-B, there is no quiescent at all, and the output devices will conduct for exactly degrees - this is rare. Class-AB amps have a very widely varying current drain, which may be only 20 - mA or so with no signal, but rising to many amps when driven. The main problem is the revolting waveshape of the current on each supply lead, typically half-wave pulses, in sympathy with the program content. These waveforms - this is current, not voltage - have sharply defined transitions, and as such will generate a magnetic field which varies with the current.
Since a sharp transition equates to high order harmonics, care must be taken to ensure that voltages are not induced into the input stages of the amp from the supply lines. Because of the low inductance of the wiring of an amp, these problems are going to create distortion components which will tend to be worse at higher frequencies.
The power supply rectifier diodes usually conduct for only a short time during each AC cycle - this may be as little as 3 or 4 degrees at idle, but both the angle of conduction and the amplitude of the current pulse will increase as more power is drawn from the supply. These amps draw a large current on a continuous basis, and place a completely different loading on the supply. The current pulses are gone from the supply leads, but the rectifier and filter now must handle the maximum current on a continuous basis.
The continuous load creates a new set of constraints on the design of a power supply, and the use of a Class-A amp implies that the builder already wants the very lowest noise. Class-D Amplifiers Class-D amps in various forms are now common. Like Class-AB amps, the supply current varies widely with output level, but some don't have very good PSRR power supply rejection ratio so the DC needs to be well filtered.
There is another problem as well, commonly referred to as 'bus-pumping'. This can be a significant issue with high power, low frequency output, and the topology of a typical single-ended as opposed to bridged or BTL Class-D amps means that the supply rail voltage increases , and can lead to overvoltage shutdown or amplifier failure.
Some Class-D amps rely on very large filter capacitors to absorb the power returned from the load, and others run two amplifiers in 'anti-phase'. As one drives positive, the other drives negative, and inputs and speaker connections are reversed in relation to the other channel.
This is provided naturally by a BTL design. Somewhat surprisingly perhaps, the fundamental requirements of the final design are not greatly influenced by the different loading presented by the different amp types described above.
There are differences of course, but in most cases they don't change the basics of PSU design. The continuous rating of a Class-A amp means that you must design the supply for a continuous rather than transient current, but since we are discussing properly designed, quality power supplies, the final result may be quite similar.
However, a continuous high current load always means the voltage will be less than expected. When a power supply is used with an amplifier, the basic things we need to know before starting are as follows. With only these three criteria, it is possible to design a suitable supply for almost any amplifier.
I shall not be describing high current regulators or capacitance multipliers in this article - only the basic elements of the supply itself. The first component of the power supply is the transformer.
Using magnetic coupling between windings, the transformer is used to isolate the amplifier and the users from the mains voltage, and to reduce for solid state equipment at least the voltage to something the amplifier can tolerate. The primary winding will be rated at , or V AC depending on where you live, and the secondary will be a more user friendly or less user hostile voltage to suit the amplifier. Contrary to what you might imagine, the maximum flux density in a transformer core occurs with no load.
This is covered in detail in the Transformers article, but it's mentioned again here because it's an important thing to understand. If you assume the 'alternative possibility', your understanding of transformer functions will lead to assumptions that are seriously at odds with reality. At light loading, this rule can be applied without fear, and it will be accurate enough for most applications.
When an appreciable current is drawn, this simple approach falls flat on its face. Mains variations: These occur in all situations, and the mains voltage at any point in time will usually be somewhat different from the nominal voltage quoted by the supplier. In nearly all cases, an amplifier is rated at a certain power output into a specified load impedance, and at the nominal mains voltage.
For those who live close to a sub-station or pole transformer, expect the voltage and power output to be higher than quoted - the rest of us can expect a lower mains voltage and less power, especially during peak electricity usage times.
Losses: Since all transformers have losses, these can be ignored in the design phase for only the simplest and least critical applications. For anything where reasonable performance is expected, you need to do more work to get everything right. Magnetising loss AKA iron loss is the current that is required to maintain the design value of magnetic flux in the transformer core. There is nothing you can do to affect this loss, as it is dependent on the size of the core and the design criteria of the manufacturer.
Large transformers will have a larger magnetising loss than small ones of the same type, but will be less affected by it due to the larger surface area which allows the transformer to remain cool at no load. The iron losses are greatest at no-load and fall as more current is drawn from the transformer.
Copper losses are caused by the resistance of the winding, and are lowest at no load, and rise with increasing output current. There is a fine balance between iron and copper losses during transformer design.
Linear Power Supply Design
After watching a movie about disasters and seeing how some of the characters called for help using a ham radio, you totally got curious about ham radios and clearly want to get one of your own. Or maybe you've gotten yours already. That's awesome. But, your ham radio is still as good as not having any ham radio at all, especially if you do not have a power supply. Just like the body of man is lifeless without a soul, ham radios are next to useless without high-quality power supplies. Now, the dilemma and confusion start here. How exactly do you know which power supply is of high-quality?
R&S®MG3500 500 W HF power amplifier
Display all pictures. By buying this product you get 2 loyalty points. Do you want to be notify when the product will be available? Add to cart. The minimum purchase order quantity for the product is 1. This power module allows a comfortable power in a volume of restricted space. Ideal for powering an Amplifier. Thanks to the use of 4 diodes FCUA , each mounted independently on a heat sink, this power supply indeed makes it possible to reach a rectified voltage of 50V. Toroidal Transformer VA 2x22V. Fuse holder 10A 6.
Commercial Audio
I am ready to re-open and the website ordering system has been reactivated. I will do my best to get orders out as I know it will be busy! Due to these supply issues, those kits are not available and have been temporarily removed from the website. When these parts become available they will be added back to the site. I am also still waiting for a new telephone line to be installed as the old one was damaged beyond repair.
Radio Frequency Transistors
Most CB's, Amateur radios, and accessories are designed to work off a 12V supply. So in order to use them at home you will need a suitable power supply. We stock a large range of power supplies from 3A to 40A. It is important that you choose a suitable size supply for your needs. Buying one smaller is false economy - at best it will not work correctly and at worst you will blow it up and possibly also damage your radio.
Linear Power Amplifiers
Project Tsunami. Burkhard, DF5XV, www. The live weight of this PA amounts to 1. Burkhard has an official permission of the BNA for 20 KW on shortwave for broadcast, although not for ham radio. Such enormous values of transmitting power challenge even the creativity of an experienced high frequency engineer. Well, three years ago, the of this article placed a bet against Burkhard to build a power amplified with more than half the output power of the VK20 in SSB mode, yet would fit the trunk of a compact car as well as a manageable weight. Burkhard's answer: No way!
For several years I have been thinking about ways to build a solid state legal-limit amplifier for amateur radio use. It's not that I would absolutely need one! But out of technical interest I would like to develop a solid state amplifier.
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