07-02-2007, 10:16 PM
Hi John,
Nothing wrong with replacing these with new silver mica caps of correct value.
But I would not put too much stock in reading value of these caps from the colored dot patterns. This can be very difficult for even those with a lot of experience, and choosing a replacement mica cap based on the dot color coding of the supposed original is a last resort. Rather, I would base my decision on the proper value as noted on the schematic and/or parts list.
Several reasons for this: Colors on the dots can fade over the years making them difficult to read, or cause one color to appear as another. Also, sometimes one dot color may fade out or peel off completely, leading you to assume that the dot is blank when in fact it may have originally been colored.
Regarding measuring capacitance of your caps, what equipment are you using to measure them with? For mica caps in pre-war Philco radios in general, I have not experienced many which vary much in capacitance from original values. Rather, the more common problem is leakage which can only be tested in a bridge-type capacitor tester at full rated voltage, such as a Sprague TelOhmike, EICO 950, etc. And the second-most common problem with them are the short leads which become brittle and limit flexibility due to expansion and contraction over the years and can cause internal "opens" which will give erroneous and/or varying readings when testing for either capacitance or leakage.
Poston
Nothing wrong with replacing these with new silver mica caps of correct value.
But I would not put too much stock in reading value of these caps from the colored dot patterns. This can be very difficult for even those with a lot of experience, and choosing a replacement mica cap based on the dot color coding of the supposed original is a last resort. Rather, I would base my decision on the proper value as noted on the schematic and/or parts list.
Several reasons for this: Colors on the dots can fade over the years making them difficult to read, or cause one color to appear as another. Also, sometimes one dot color may fade out or peel off completely, leading you to assume that the dot is blank when in fact it may have originally been colored.
Regarding measuring capacitance of your caps, what equipment are you using to measure them with? For mica caps in pre-war Philco radios in general, I have not experienced many which vary much in capacitance from original values. Rather, the more common problem is leakage which can only be tested in a bridge-type capacitor tester at full rated voltage, such as a Sprague TelOhmike, EICO 950, etc. And the second-most common problem with them are the short leads which become brittle and limit flexibility due to expansion and contraction over the years and can cause internal "opens" which will give erroneous and/or varying readings when testing for either capacitance or leakage.
Poston
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