Confusing Resistor Values in Latin + More

So you are new to radio repair, and the schematic for that 1923 radio says "2M" in the description for a resistor.
 You dutifully check that resistor with your ohmmeter, and by golly, it measures 2000 ohms, not 2 meg.
 So you replace it with a 2 meg resistor like the schematic shows and the radio still doesn't work, and the voltages are way off in that circuit.

Well Grasshopper, there is a reason. Back in the days of stone knives and bearskins, they had no standardization of electronics notation.

 Many manufacturers used LATIN Numerals in the part notation.
 You know, the old courthouse you drive by has "Built in MCMVII" over the door.
 Yup. Some folks used the Latin"M" (You DID take Latin in school, didn't you?) as a designator for THOUSAND. 

Now this even slightly confused me for a few minutes until I quickly realized they were using the Latin "M" for thousand. (How I came to this conclusion really quick might have been from my history studies, .....or just pure dumb luck, likely the latter :geek: ).

Then came the RIA, (Radio industries Assn.) and some other groups that tried to "standardize" parts notation.
 There were several different symbols for grids, plates, cathodes, resistors, capacitors, etc. It was VERY confusing.

 Then to add more to the confusion, many of the radio mfgr's. used either sodium or mercury vapor lights in their factories. 
  The so called "Standard" color codes would not show up properly in those types of lights. So they used their own special resistor values so that the assemblers could actually see the value of the parts they were installing.
 Example: a 5K resistor was used instead of a 4.7K as the green was visible in the light they had and yellow was not. This explains why you run into some really odd value resistors you can't find any more in the early sets.

 Then EIA came along (Electronics Industries Association) and did a pretty good job of standardizing notation and values of parts.

 You will still find some "odd" notation on schematics from Europe and Asia. Well there is no such thing as a perfect "5 Year Plan".

 (Wait until you find a very old radio with a wax coated, tubular capacitor marked ".000010" mfd., or a mica capacitor marked 10 mmf, or the "new" resistors from Europe or Asia marked 4R7 on a schematic. That last one confused the heck out of me until I looked at a schematic and the actual part.)

Then to even add more to the confusion, one company made resistors in a "mica" capacitor, "postage stamp" type case, that was half the width of a normal "postage stamp" mica.

 That one, I must admit, bit me in the shorts. I couldn't figure out the odd "mica capacitor"I salvaged out of a junk radio chassis, or why it wouldn't properly test on the capacitor checker, and they all tested leaky. "Hmmm. the color code on the bakelite case says its a 1500 mmfd capacitor, but it tests at 1500 ohms??? "
  A moment of Zen concentration, where I sat in the Lotus position and chanted "Ohm" for an hour. Magically,  Enlightenment occurred. 
(OK I admit, I broke one open and found it had a resistance wire inside. Yeah, I cheated, so what?)

Then we get into the "oddball" capacitor blocks that many mfgr's. used, and the really confusing "Bakelite block condenser/ resistor combo's " that Philco delighted :twisted: in producing. 
  Yes, the did save space, but you were supposed to replace the entire block when the condenser/resistor in it went bad.
 (Nice, but this is 80 years later & Philco & the others went down the toilet a long time ago). You gotta replace the block with individual parts, or melt the "goo" out of it and install new parts inside. And NO! You can't just solder new parts to the terminals on the outside of the block, as the parts are still bad inside it. You don't solder new filter capacitors across bad ones do you?

 There is a good ref. book out on the Philco Bakelite Block Condensers. If you work on Philco Radios, it is a "must Have".