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The text on this page is intended to help those individuals who have limited experience with electronics building and operation. It is not an attempt at training, but to offer some tidbits and hints that I feel everyone can benefit by.... Foxy CAPACITORS:: I have always had a problem with the conversion of values of Capacitors. So I have the following chart to help. Pico-Farads nano-Farads Micro-Farads Code 1pF............................... .001nF................... . 000,001uF 10pF........................... .01nF..................... . 000,01uF 100pF........................ .1nF....................... . 000,1uF ...................101 1000pF...................... 1.0nF.................... .001uF .......................102 10,000pF.................. 10nF.................... .01uf..........................103 100,000pF............... 100nF.................. .1uF...........................104 1,000,000pF........... 1,000nF.............. 1.0uF..........................105 10,000,000pF........ 10,000nF........... 10.0uF........................106 SM ( Surface Mount ) Capacitors These capacitors are hard to read. They contain two marks, a lettter and a number. The value given on the SMT capacitor is in picoFarads. A=1.0, B=1.1, C=1.2, D=1.3, E=1.5, F=1.6, G=1.8 etc............................... 0=1, 1=10, 2-100, 3=1000, 4=10,000, 5=100,000, 6=1,000,000, 7=10,000,000, 8=100,000,000 and 9=.1 Thus a SMT Capacitor marked as D4 would have a value of 13,000pF A complete listing of SMT Capacitor markings can be found in the A.R.R.L Handbook. Mounting SMT Components can be intimidating. The things needed are: a good pair of tweezers ( not the sharp end kind but the flat blade type ), an eye loop ( the hood type with binocular lens), a small tipped iron, and small gauge solder. I find that in mounting an SMT part, I tin one of the pads first , leaving a small bit of solder. Using the tweezer and holding the device onto the pads ( like you want them to be ), heat the presoldered pad, and the end of the SMT part. This will solder the part to the one pad, and then you are free to solder the rest. Caution!! Don't stay too long on the other end(s) or the component may come loose from the initial solder point. Hints: Capacitors are capacitors aren't they? Yes and no. There are some places that a certain type of capacitor is not recommended. For example, it is not a good practice to use a Metalized Mylar capacitor in a digital circuit. Why? because a metalized mylar capacitor is a self healing capacitor. If a breakdown occurs, that area is "blown clear" and the capacitor will continue to function. Nice, but in the blast, a pulse occurs, and it can mess up a timing operation no end. Tantalum Capacitors can be used for coupling, but one must be extremely careful of observing the initial (DC ) polarity between devices. Is this enough? NO!. One must take into consideration the dynamic values (AC ) as well. Many a design has been messed up by using tantalum capacitors for coupling. If a great value of capacitoance is needed, then it is possible to use two tantalum capacitors back to back. Ceramic Capacitors are great and fairly stable, however their tempertaure coefficient can cause a vfo to drift badly. Negative coefficient ceramics can be used to counteract the drift. Silver Mica Capacitors are probably the most stable with respect to their initial value. A word of caution..... In using capacitors of any type, the initial value can be drastically changed with excessive application of heat. The same is said for Resistors. PC Boards and Component mounting. PC boards come in various packages. Some are compressed laminate material, and some are Fiberglass. Both are fine for the Ham application, but over time, the laminate board can and will absorb moisture, and for RF designs, this can be disasterous. The glass board is the one to be preferred. When fabricating any design on a PC board, one should be careful to look at each finished solder joint. If the joint covers the lead ( barely) and is bright, it can be considered a good joint. When the word barely was used, it means, Don't pile the solder on top of the lead and pad! There is a good reason for this statement. The lead under all of that pile of solder may still not be soldered to the pad. The finished solder joint should be bright. If the joint is dull and has a grey appearance, it could be a "Cold" solder joint. I have found, on many PC Monitors, cold solder joints causing changes in color, and apparent jumping of the picture. The cure has often been to reheat suspect joints. A word of warning. Do not depend on solder to hold a part through a PC board pad. Solder has a lousey creep strength. It was found, in the early days in Ireland, that the milk cans ( the bottoms soldered on ) would leak after a year or two. It was discovered that solder had a very poor mechanical bonding strength. At NASA, the same thing was rediscovered. Mechanical bonding of electronic components was dependent upon solder to do the job. After some failures, all leads and protrusions through a pc board had to be bent against the pad before soldering. Transistors. The following are some remarks that can be useful to the inexperienced ham. These remarks are intended to be guidelines you may follow in sizing up and using a transistor. The NPN transistor has current flow from the collector to the Emitter.the base also flows from base to the emitter ( all arrows point to the emitter ). The PNP flows opposite. In a silicon transistor, there is alsways a .7 volt difference( in a good working transistor) between the base and the emitter. For the NPN the bse will be .7volts higher than the base to ground. In the PNP it will be .7volts lower. In a Germanium transistor, the base on the NPN will be .3volts higher in a NPN and >3volts lower in the PNP. The Beta of a transistor gives some idea of the gain of the device. The beta of a transistor will vary with temperature. Mostly it will increase with temp, and decrease with decrease in temp. A good use of beta is to determine the "reflected impedance in the emitter circuit back to the base. example: if there is a 100 ohm resistor in the emitter leg to ground with a transistor whose beta is 100, the reflected resistance in the base circuit will be 10,000ohms appx. On the other hand, a capacitor whose reactance is say 1000ohms at a specific frequency base to ground, the effective reflected capacitance in the emitter will be larger than the base by a factor of 100. e.g. it will look like a capacitor whose reactance at that same frequency will be approximately 10ohms. I believe this is referred to as the" Miller effect." Internal capacitances vary widely in many cases with small changes in bias, hence if yhou are hard pressed to find a varactor, a transistor can be used. One final hint about Transistors. If a transistor is rated at some "power", be advised that that power rating is given based upon an "Infinite heat sink". There is always a heat sink derating factor given for every transistor. GLOWBUGS (vacuum tubes)... This may come as a shock to the new experimenter, but contrary to all belief, the vacuum tube is not dead. In fact, in several uses, I feel that the vacuum tube has it all over the transistor ( to date ). There are still many small vacuum tubes that are to be had on the market, and sockets to match. The vacuum tube is much more forgiving than the transistor. If one wants to experiment with the vacuum tube, there are still tube manuals to be had which give all of the details of every vacuum tube. One by RCA, and one by Sylvania. Both of these books are in reprint. They can be had by looking on the net for Amazon or Barnes and Noble. One hint that I can offer at this point; if one is to try and drive a "vacuum tube final" with a transistor exciter, be advised that most of the finals are grounded grid construction and trying to adjust the transistor exciter , bypassing the final, and then driving through the final, one will discover immediately that the nice load that one had before going through the final has changed drastically. The solution, place a small tuner between the exciter and the final. Tuning a Glowbug final. Here is the scoop. There is "Main Tuning, of Plate Tuning" knob. There is also a control called "Load or Antenna ". The procedure is as follows: 1. use a very small amount of drive from the exciter to the final, just enough to get the Plate current meter to read upscale. 2. while the exciter is driving the final, rotate the Plate tuning ( watching the plate meter) and tune for minimum current. You might have to rock past and back and forth until you are satisfied that the plate circuit is in resonance. 3. tune the "antenna or Load" knob until there is a rise in plate current. don't increase the current too much. 4. go back to the plate control knob, and readjust for a minimum current again. 5. adjust the antenna load until the current rises again. 6. redip the plate tuneing. 7. keep this up until the proper plate current ( the recomended amount ) is obtained. The final is now in resonance. If you are using an antenna tuner with a roller inductor, Never try and adjust the VSWR with more than minimum power applied.
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