Looks like a great site!<P>I want to build a fairly simple transistor radio - block of wood, hand wound coil, two to three transistors.....<P>Couple of questions:<P>The schematic for this regenerative receiver calls for two 2N2222 transistors. I bought them today and was wondering how you determine which lead is the base, collecter, emitter? The transistor is the black composite material type with one flat side.<P>The schematic also calls for some capacitors. The required "pF", "nF", and "uF" units are shown. When I got to the store the capacitors were marked "pF" or just had a number stamped on them! How can I determine the correct units so I can buy the correct capacitors?<P>I also have to make some "inductors" for the set. Do I use certain lengths of ferrite rod with windings to get the correct "uHy" and "uH" I was told what the "uHy" and "uH" values are supposed to be, how do I determine how much ferrite and how many turns I need to have? <P>Maybe this radio is just a little too complicated. Should I just go with a simpler radio that uses a coil wrapped around a cardboard tube or salt box? Anyone have a simple schematic that they would like to share?<P>Thanks!<P>Huron<P>------------------<BR>

Hi Huron<P>For the transistor basing see the picture, as crude as it is, in the gallery. For capacitors, say you have one marked 103. This is a .o1 uf, just count back 3 places from between the 0 and 3. If it was 104 it would be a .001uf. To convert from pf to uf count back 6 places from the end of the number,i.e 2700pf =.0027uf. For nf to uf count back 3 places.<P>Chokes use a lot of math formulas that I just can't remember. Hope I've helped you some. <P>------------------<BR>Jim

Jim,<P>Thanks for the help. Makes sense!<P>------------------<BR>

Oops, typo, 104 is 0.1µF.<P>If you're using microhenry-sized coils, air-core is perfectly feasible, and simpler than getting ferrite specs. Unless you really need the smaller physical size.<P>------------------<BR>

Alan I thought it was counting back from in front of the last number...so you say 103 would be .1 and 104 would be .01?<P>------------------<BR>Jim

Hi<P> 103 is .01 mfd, 104 is .1 mfd. Value is in pf listed as 1 followed by 0 and 3 zeros. 103 would be 10,000 pf or .01 mfd. <P>------------------<BR>Norm

Post the values you need here and we'll help ya convert 'em to an appropriate value to shop for. That'll be the easiest way to start. You'll get onto it once you see how it all fits together. <P>Basically, the "unit" of capacitance, the farad, is so huge that any realistic value is a tiny, tiny fraction of one farad. Hence, you see pico, nano, micro etc. Microfarads, or "uf" used to be the norm, now it's "pf" mostly and some "nf" just to keep you on your toes! I guess it's easier to say "gimme a thousand picos" or "make it a nano, Fred!" than to say "I need a .001uf disc". <P>Most small disc capacitors these days use the three digit code mentioned in the posts above, i.e. 103, 104, etc. The first two digits are the value, read it as 10 in the two examples above. The last digit is the multipler. <P>Since with microfarads you're multiplying a fraction, you're removing zeros and getting closer to the decimal point as you multiply. Picos and nano are expressed as whole numbers, though they still represent a tiny fraction. So rather than saying "one millionth of a microfarad", we say "one picofarad" instead. Same thing, expressed differently.<P>Here's a list that'll maybe help ya. First is the number you see on the disc, its value in microfarads, then picofarads. Of the 5 examples given below, 101 is the smallest capacitance, while 105 is the largest, but obviously there are many more values available much smaller and larger than these.<P>101 = .0001uf = 100 pf (10 with 1 added zero)<BR>102 = .001uf = 1000pf (10, now 2 zeros...)<BR>103 = .01uf = 10,000pf (making sense now)<BR>104 = .1uf = 100,000pf<BR>105 = 1uf = 1,000,000pf<P>With that under our belt, let's try some others.<P>473 = .047uf = 47,000pf (47, then 3 zeros, easy!)<P>33 = .0033uf = 33pf (no zeros, that's the direct value in picafarads)<P>223 = .022uf = 22,000pf<P>Similarly, nf is used as a convenince to be able to express a buncha picos as a smaller number. It's in between pf and nf. <P>1nf = 1000pf = .001uf.<P>If you've followed this far, you now possess the ability to confound most parts desk employees! Just go ask for a nanofarad disc and see what kinda looks you get! <P>Some older discs are marked in uf's, so you'll always see the decimal before the number as your clue to that. Tubular types are also usually marked in uf. Some types even give the symbol, making it almost foolproof!<P>Coils and chokes are tougher, you may need to add turns or take them off to get a homebrew coil to work in your circuit. Nowadays, LCR (Inductance, Capacitance, Resistance) meters are getting pretty cheap, and you can use one to read the values of these parts directly.<P>I bought one of the Radio Shack trainer gadgets, the manual that comes with it has a good description of how to convert the pf and uf values and how to read the common parts types of transistors, resistors, capacitors, etc. It also includes circuits and all needed parts for the radio you mention plus lots of other simple circuits.<P>In the parts aisles you might find bags of disc or electrolytic caps and bagged assortments of inductors/chokes, resistors, etc. The trainer makes it easy to swap in different parts without harm. <P>Once you get your circuit working you can attempt to move it to a board and see if it needs changing to work in that arrangement, as changing parts positions and wire lengths can sometimes alter the circuit. <P>Even a short wire is not merely a simple conductor, as it has a measureable resistance, it also has a small added capacitance and inductance. You have to design while thinking of the circuit as a whole, not just an assembly of parts. As you've already assumed, it's best to start small, clean and simple.<P>Of course you don't need the fancy trainer, just pick up a few bags of mixed values and types, some breadboard or perfboard and have fun!<P>-Ed<BR><P>------------------<BR>

Hi Huron, I'm surprised the instructions don't give some coil winding details. I assume it's a simple circuit with a single (aerial) coil, perhaps with regeneration (a feedback winding). If this is the case, just try about 70 turns on a ferrite rod and see how it works. It should be OK but if you have too many turns it will tune too low in frequency ( miss the top of the band) and too few turns will miss the bottom of the band. You can alter the number of turns to correct. Sliding the coil along the ferrite rod will trim the inductance slightly. Try about 1/4 the number of tuning turns for the feedback winding. Have fun, you'll get it working with a little trial and error.<BR>Don Black.<BR>PS is it possible to post the schematic please?<P>------------------<BR>