Figure 1 shows several pushpull tube amplifiers only the power tubes and the output transformers primary winding. Calculation of output transformers the output transformer is probably the most expensive part in the amplifier and something you have to live with if you like classic tube amplification. It also includes some history and the authors suggestion for the future of these devices. Since impedance varies as the square of the number of turns, the primary impedance for a power tube screen is 18. Classic tube output audio transformer overview hammond mfg.
The problem lies with the way many transformer vendors rate the power capability of their transformers. To separate the high voltage and match the speaker impendance with the tube impendance we need audio grade output transformer. A little input on audio output transformers pearl hifi. Output transformerless amplifier designs otl but most tube amps use output transformers. The objective of this project is to develop an output transformer for singleended tube amplifiers with. The frequency range and time behavior of output transformers, used in tube amplifiers, are determined by the transformer parameters and the impedances of the source and the load. I started with almost no knowledge in electronics and with no tools. Power transformers do not change power levels except continue reading power. Assuming an ideal transformer and the phase angles. Since 6v6 impedance is about double that of 6l6s, and youll have two in parallel per side. In this project, the 2a3 power tube runs at a 60ma plate current with no signal applied and has a 410v plate voltage. Emf equation of transformer single phase transformer. Whether you are into the clean, free spirited single ended tube output or high efficiency, high power, pushpull audio, we have the output transformer for you.
S note that the order of the numbers when expressing a transformers turns ratio value is very important as the turns ratio 3. Understanding your output transformer part one by mark. Modern transformers are designed to closer tolerances than transformers in the past. I dont always spend as much time on my power supply designs as i should.
The transmission line transformer the tlt transmits the energy from input to output by a transmission line mode and not by fluxlinkages as in the. We have been producing tube output transformers continuously for over 75 years, constantly improving and tweaking their performance. An output transformer for pushpull operation, with reactive load of 8k ohm, provides each vacuum tube with a load of 4k ohm, when operating in class a. The wattage output in an amplifier may vary from application to application due to many variables such as tube types, solid state vs. This is a type of transformer for matching balanced transmission lines or cables to, or from an unbalanced input or output, the device is reversible. Electronics tutorial about the audio transformer which can be used as a line. It is hoped that future device development and application will be encouraged. Because the 2a3 tube is a directly heated triode, the cathode and filaments are connected, so the design must avoid hum. Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. A transformer in which the output secondary voltage is greater than its input primary voltage is called a stepup transformer. Basically a transformer consists of a core of a material that can be magnetized wound with two coils. The fundamental consideration is that the core must not go into saturation at any voltage or frequency.
The turns ratio between the input and output wire coils provides either an. This will affect your transformer selection and your overall power supply design. The goal of this book is to show the world how an output transformer or opt may be designed and what to think of. Designers comments to his great joy, through the years mr.
The 2a3 tube amplifier a tribute to simplicity and warm. Moving coil phonograph cartridges produce a very small voltage. My goal was to start building practical projects and amplifiers and learn theory along the way. For the primaries of output tubes, this can be up to a couple of hundred volts, so dont think that you can relax your safety precautions it can still kill you, even driven with 3vac on the secondary of the output transformer. The early jtm45s used the rs deluxe output transformer which had 6. Output stage the major factor involving the design of this single ended output stage is matching an available output tube to an available output transformer ot, which can provide the proper impedance matching. For this to be amplified with a reasonable signalnoise ratio. Figure 1 shows several pushpull tube amplifiers only the power tubes and the output transformer s primary winding. Opt design wikibooks, open books for an open world. The two power tubes are replaced by a voltage source. Most of those dreams came true and others are on the. A main ht transformer 300 volts at 300 ma b anode current meter c tank circuit d ht dc smoothing choke 3 h at 250 ma 52 ohms resistance. The transformer as stated in the preface, the transformer is very important, and we shall in this chapter look into the properties and problems of the output transformer. A main ht transformer 300 volts at 300 ma b anode current meter c tank circuit d ht dc smoothing choke 3 h at 250 ma 52 ohms resistance e modulation transformer 9 k anode to anode and 3.
Lundahl transformers old fashioned 30w push pull amplifier. Ultralinear operation, also known as distributed load operation, is a term when applied to singleended or pushpull vacuum tube audio amplifiers, that describes the particular output stage configuration whereby the screen grids grid 2 of tetrodes, pentodes or beam power tubes are fed from a tapping in the output transformer singleended. Looking through all of my scavenged transformers i cant find a single one in the thousands of ohms, most are a few hundred and lower. The output transformer is probably the most expensive part in the amplifier and something you have to live with if you like classic tube amplification. Aug 05, 2016 video lecture on emf equation of transformer of chapter single phase transformer of subject basic electrical engineering for firstyear engineering students.
Video lecture on emf equation of transformer of chapter single phase transformer of subject basic electrical engineering for firstyear engineering students. For those new to electrical theory, all audio signals are ac. This means that a single spp board is used with one power transformer and two output transformers to make a stereo hifi amplifier. While transformers are not required, as in tube circuits, a precision input transformer will optimize the opamp to the source impedance, which is. The output transformer is the heart of a valve amplifier. Enough to motivate a short paper with some comments on the above. The one thing im stuck on is the output transformer, according to the datasheet i need to get a 35004000 ohm transformer with a 4 ohm output to power a car speaker i have. Audio transformers tube output transformers lundahl. So, something like a super reverb output transformer would work. Basic transformer operation can be described by two formulae relating the transformation ratio to the turns ratio of the transformer windings. Guitarists, bassists, hammond organists and other musicians know, without having to think about it, that the sound they want to achieve is only possible through the use of tube amps and tube preamps. Output trannys contribute most of the distortion in a valve amp and have a limited bandwidth.
There are several things that are important in getting an output transformer made. Despite the theory the steeper the invertedv the worse it is, 90 degrees is about the tightest it ought to be. Figure 9 shows the lowfrequency equivalent circuit of this amplifier, seen from the primary side of the opt. The output transformer is an important part of the amplifier requiring a. Valve tube amplifiers almost always use an output transformer to match the high load impedance requirement of the valves several kilohms to a low impedance speaker smallsignal transformer. If transformer t4 couples the if stage to the preceding converter stage. Chosing a replacement output transformer now lets assume we have a set that has an output transformer with an open winding that must be replaced, and the output tube is a single 6f6.
Nov 18, 20 amps that use this smaller 28watt transformer are always going to have that certain compression and dynamic that defines an output transformer going into saturation. Thus, effective, regular maintenance and testing is even more essential to. The drive circuitry of the control grids is not shown i assume perfect. A mcintosh audio amplifier incorporating a trifilar. The halfprimaries of the output transformer should have identical voltages on them. Assembly manual schematic parts list tubes and applications. The stepup transformer decreases the output current for keeping the input and output power of the system equal. It was suggested that you could put an 8 ohm load on a 16 ohm 5k primary transformer to get a 2. If you would like to simply calculate number of turns and other aspects of your output transformer for a pushpull tube guitar amp or a home hifi tube amp, dont miss out on this tried and tested method which is an easy to use excel spreadsheet that automatically calculates the transformer windings according to your needs. My dream was to wind my own transformers one day, design my own circuits and make guitar tube amps and mic pres and tube mixers. The circuit exhibiting the distortion being downstream from the output tubes biased into.
The most common purpose of a power electronic transformer is to convert alternating current a. A transformer does not pass dc, therefore a transformer can be used to keep the dc voltage on the output of an amplifier stage from affecting the bias of the next amplifier the ac signal is coupled through the transformer between amplifier stages. There is no real standard for specifying the power handling capabilities of an output transformer. Apr 30, 2010 the output transformer is the heart of a valve amplifier. Byrith has received a number of comments and questions from builders of this amplifier. A general theory will be discussed on how to calculate the frequency range and time behavior of output transformers in conjunction with output tubes and loads. By setting the anode bias current to 28ma, we obtain the loadline depicted by the red line, which stays below. Using typical operating parameters laid out in 1, the 6v6 power tube, operating. At the time this manual was written, the tubelab spp has only been tested as a stand alone push pull amplifier. Whether its an inter stage connection in a tube amplifier, or multiple solid state devices connected. Kt66 push pull output transformer tube amp information.
Accepts the intermediate frequency signal from the converter, amplify it and pass it on to either, the next if stage if the receiver has one, or to the detector stage. Also required is the mains voltage and frequency where the amp is to be used. Audio engineering society, october 1987, ukpdfgavs. Geigermuller counter circuit theory mit opencourseware. Output transformer less amplifier designs otl but most tube amps use output transformers. The anodes are connected to the primary winding, the cathodes to ground circuits 1, 2, and 3, and the middle of the primary to the highvoltage supply.
I volunteered to put a 4 ohm load on my amplifier and re run the tests. A simplified analysis of the broadband transmission line. Electronic fluorescent lamp ballast stmicroelectronics. By setting the anode bias current to 28ma, we obtain the loadline depicted by the red line, which stays below the 12 watts max allowed anode power dissipation.
Wallman editors vacuum tube amplifiers mcgrawhill book co. This varying load impedance is reflected back to the primary, so the tube, and output transformer must work into a varying impedance range. Pushpull output transformer spreadsheet calculator with. Another common purpose is to provide electrical isolation between electrical circuits. Amps that use this smaller 28watt transformer are always going to have that certain compression and dynamic that defines an output transformer going into saturation. The function of an opt is to lower the high voltage to safe values and to multiply the weak tube currents into larger values. The basics of current transformers nk technologies. Or, a 2 6v6 transformer that can handle the extra power not sure they exist with half the specd speaker impedance load connected to the output. Tube power supply design its time for a little confession. Understanding your output transformer part one by mark baier. This action is performed by winding different amounts of turns on the incoming primary and outgoing secondary side of the opt.
Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932 phone. A discussion had been ongoing on the diyaudio forums about these transformers, and questions were raised concerning the few impedance selections that were available. Secrets of output transformers dali technical sales. Document resume title resonant circuits and introduction to. Audio transformer is the primary part of a tube amplifier which generates an electromagnetic field. In contrast, the larger bassmansuper reverb trannies will relate the vacuum tube and circuits clipping before the tranny hits the ceiling, which accounts for the fast, grainy. Singleended classa tube amplifier design and construction.
Many state the facts, but they are not fully understood, and some just flat out lie. In tube amplifiers you need an opt because the voltages in the tube. The two output trannys are rotated 90deg to the power mains tranny to avoid picking up induced hum from the mains tranny external magnetic field. Understanding impedancein audio transformers introduction the term impedance is the backbone of all things audio, fundamental to understanding how an ac circuit be. Core losses due to hysteresis and eddy currents in the core are represented by r c. Type of winding ratios rating of windings output v. An easily constructed highquality singleended 8w amplifier.
Considered a stepup transformer shown in the figure below. Most of our opts can be configured for different primary and secondary impedances. Tube amplifier output transformers all opts are built in our dual coil single ccore style and can be ordered with a choice of core airgap for pushpull or singleended applications. Building a tube amp, how to calculate output transformer. The screen taps in output transformers designed for ultralinear operation are typically set to 43 percent of the primary winding, which is the point of minimum distortion. Since a transformer does not create power, the power output from the secondary of an ideal transformer can only equal and in a real transformer only be less than the power input to the primary. Note that the circuit shown has no filament preheating however it would be possible to add circuits such as those described later for the pushpull topology. Basics, maintenance, and diagnostics vii contents continued page 4. To separate the high voltage and match the speaker impendance with the tube impendance we. Sometimes i get excited about my latest circuit and after looking for just the right tubes, output transformers, coupling caps, and low noise resistors, the power supply design becomes almost an.
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