It seems that replacing the capacitors is not the magic bullet that I thought it was. Has made little difference on the ones I tinkered with so far, but I think its because I am not doing this precisely enough.
Anyway, I have a Packard Bell 501 which uses the 'American 5' set of tubes. All I ever got was a loud hum, so I replaced all the tubes with known good ones. Still loud hum. I then started replacing the caps one by one. Still loud hum.
The two that I did not replace were two .05uf ones that were wired in paralell but the radio did not call for .1 so I don't know why are are there. I have the schemtatic and those things are like reading greek. I keep trying trace from the numbering of the tube prongs on the underside but thats darn right confusing. Does reading schematics get easier? I hope so.
Anyway, I have to study the schematic some more. The two .05's are wired together but split where the hot wire comes in from the outlet - one .05 is coming off there and going into the combined. The other lead is grounded? Anyway this is hard to visualize. I will try to post a picture soon.
I have bought a few books the last month trying to bone up. I have the one by David Johnson and just got one from Jim Carr.
I will keep plugging away at it.
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Schematics are not hard to read once you understand exactly how tubes and radios work. They are pictural symbols for components. For instance, you see a condenser (capacitor). It is symbolized by two plates. The reason for this is because in reality there are two plates in a condenser that are spaced apart. They never touch. Electrical charges are built up between these plates. Larger condensers respond to lower frequency current changes. Smaller condensers respond best to higher frequency current changes. This is all relative, too, because frequency response in relation to condensers also has to do with the impedance (resistance) of the circuit that the condenser is used in.
Books like David Johnson's Guide to Repairing Old Radios, will help you with schematics. Many books can be found at www.tubesandmore.com.
Here are some hints when working on radios. When working on the relatively simple AC/DC radios, if they hum, suspect the electrolytic condensers (capacitors). They will have high values, like the typical 50 and 30 MFD values. Be sure to put the new ones in observing proper polarity. Electrolytics have a polarity, and this must be observed or they and/or the power supply will be ruined. Generally, in an AC/DC radio, anything that comes off of the cathode of the 35Z5 or 35W4 or 117Z6 or 25Z5, and various other rectifier tubes, will be positive. Connect the positive side of electrolytics to these points (resistors, field coils, etc.). Generally anything that comes off of the line switch, which connects to the other side of the line cord, is negative (one side of the line cord will connect either directly or indirectly to the rectifier tube, and the other to the line switch).
Replacing tubes does not often correct hum. Only on rare occasion, when a heater to cathode short is experienced, does hum become eliminated by replacement of a tube. Replacing of tubes normally only corrects these problems: burned out filament, weak performance, distortion in the audio, low voltages observed within the radio.
It is best that you purchase a tube tester, as this will show many of your troubles. The EICO 625 is inexpensive. The older version is actually quite attractive (should have a closing lid, but some don't anymore). It and many other types can be found on eBay. Operation manuals can be found on this web site (Nostalgia Air) for the EICO 625 and many other tube testers. Schematics for this tester may be found here as well, should trouble be found inside the tester. Generally, when purchasing a tester of this vintage, should it be in working order, all resistors should be checked and replaced as necessary. If they drift high in value, your tube tests will be inaccurate, often leading to tubes reading "weak" or "replace," when in fact they are good.
You should purchase a signal generator, too, preferrably one that is brand new and of good quality (www.tubesandmore.com), but older ones that are known to work well will do a fair job (found on eBay and local flea markets, ham clubs, etc.). Poor performance of a radio can also be caused by mis-alignment, should no faulty resistors or condensers or other components be found. Replacing tubes will not correct this trouble. A signal generator of good quality is all that can be used to align your radio for optimum performance. Distortion in the audio section can be (and is more likely) caused by either resistors that have drifted high in value, or condensers that leak. Weak tubes in the audio section will often cause the output wattage to be lower, but if the tubes check out fine, suspect bad resistors and condensers, and/or trouble in the power supply section. All condensers should have absolutely NO leakage...not even in the millions of ohms. A leakage that is barely detectable on your meter is enough to cause trouble in some sets. The needle, if it moves up at all, should drop right back down to where it started. The most sensitive resistance check setting should be used on your meter--the one that causes the needle to move when the leads are touched by your hands. Do not touch the leads when making tests.
On rare occasion the output transformer on the speaker of your radio can open up or otherwise become faulty. Other coils in the radio may do this as well. This is not a common occurance, though it does happen on occasion.
When working on your radios, be sure that you are checking resistor values. To do so, disconnect one side of the resistor so that you get an accurate reading. If condensers are re-used, be sure to check these, too. They cannot have ANY leakage (except for electrolytics, which can have an acceptable 10 MEG leakage). If a condenser has even several million ohms leakage, it should be replaced.
Keep in mind that with your unknown condenser situation, that sometimes people make modifications to a radio. Generally, with an AC/DC radio, there is a condenser connected across the line cord to eliminate some interferance. If the chassis is not directly connected to the line cord, it will be connected through a condenser to the line cord. Generally this will be the side of the line cord that goes to the AC switch. The condenser should be connected after the switch so that it is turned off with the rest of the radio. Most of the time a condenser should never be connected from the "hot" side of the line cord to the chassis. The "hot" side of the line cord is considered the side that goes to the 35Z5 or other rectifier tube. Connecting a condenser from this point to the chassis will often cause hum troubles similar to the electrolytic troubles listed above. If someone connected a condenser at this point, and the chassis is not connected directly to the line cord, remove this condenser. Condensers of small value (.05 to .1 MFD) are occasionally placed from the plate to the cathode of the rectifier tube. Sometimes, too, they are placed from the cathode of the rectifier to the return side of the AC cord (switch). This is fine.
All in all, if you have trouble with your radio and something doesn't look original, put the radio back to the way it originally was supposed to be (assuming that you are sure you are looking at the correct schematic). The radio originally sold from the store, so it likely was originally designed to work fairly well. As you go on with your radio repair venture, you will notice that sometimes radio manufacturers put things in their radios that do not match that which is listed on the schematic. Read any notations about mid-season changes made by the manufacturer. If you change things back to the way they were originally shown on the schematic, make clear notations about how you changed things and how you originally found things. This way you can put things back to the way they were when you found them, should things not work out well for you. Also, on rare occasion you may find an alteration in the radio that looks like it was factory made, and yet it may have been made by someone other than the manufacturer. Usually you can tell when solder joints are original and all. Time will show you more and more. Just be thorough and take notes. Purchase those books and read them. Schematics are easy to understand once you get to know them. There are variations on the symbols used, and you will learn these as time goes on. The schematic represents in a pictural form, exactly how each component functions in theory (such as condensers, tube grids, etc.). The only symbol that is kind of weird is the resistor symbol. I don't think that there is an easy way to represent something that resists current flow, so they show a zig-zag symbol, which kind of gives you the idea of a hard path for current to flow through. Early schematics for tubes also use this symbol to represent grids. This represents somewhat how a grid actually looks. More modern schematics show a dashed line, which shows more of the grid's electrical function (how the electrons can flow through the spaces on a grid, but the grid can influence the electrons).
Thomas
hi dave don't get discouraged i've been working on sets for a couple of years now and although i usually get them fixed i'm in over my head much of the time but when i look back i feel i've come a long way. there are a lot of good peaple on these forums like thomas who help when a guy gets stuck and at least for me radio repair takes a long time to learn but if i can get it in my thick skull so can you. i still have to study schematics a long time before i can get it but it gets easier all the time the worst thing is everything is there but not where it is in the radio. but it isn;t that bad after awhile. start on easier ones that are just am instead of one with several bands and complicated circuts at first then later on the complicated ones won't look so confusing.i know how you feel at first i thought i'll never understand this stuff why am i even fooling with it but if you keep at it you will fix it then you think that wasn't so bad after all, at least till the next one but with each one you get a little smarter so don't give up. butch
T.D.
hi thomas it doesn't matter how old you are you give good advice and have a interest in old radio's.idoubt there's many around who worked on them when they were new the principles don't change just the parts get harder to find.butch
Thomas
As you study, try to remember that the schematic can be viewed as a collection of smaller circuits that feed into each other. Maybe the easiest section to understand is the part that conditions the power. In an AC set there ought to be at least a rectifier tube, a transformer, some resistors, and some caps for conditioning and filtering the power to the rest of the radio.
Something that might also make the schematic seem odd is that this is a picture of how things look "electrically" and may not be exactly how things look "physically" in your radio.
For example, let's say you have two parts on the schematic that connect to ground but are not drawn
connected to each other. In the box though part A may be connected to part B which in turn is connected to ground. This is not how it was drawn but is electrically identical to the schematic.
There should be an oscillator section, an amplifier section, an IF section, an output section. Much depends on the number of tubes your radio has and the number of bands it is capable of detecting.
If anyone finds I'm all wet on any of this, please correct me.
Don't give up though. It gets easier as you go. Even after you succeed there may still be hurdles. After I finally got my first radio working, it failed a couple of weeks later. Just using it frequently after 50 years of sitting stressed a couple of resistors to exceed tolerances (I had previously checked them out as OK). But because I knew the radio inside out by then, it was a quick fix.
Believe me, after you get that first one working, you'll want to try another. The journey really is the fun part.
Randy D