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Resistor and Capacitor values in old circuits
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Return to top of page · Post #: 1 · Written at 7:23:59 PM on 30 May 2014.
	Airzone Location: Maclean, NSW Member since 30 May 2008 Member #: 291 Postcount: 341
I am looking at a circuit for a STC-543T J & U console radio. The resistor values show 05, 02, 01 then the other values like 3000Ω which we all know. Are the values 05 actually .05Ω or .05kΩ ?? The capacitors show 00001, 01, 001, 006 etc. Should these values have a decimal point at the front making them .0001μF ? etc The circuit is not very clear. Peter

Return to top of page · Post #: 2 · Written at 7:59:56 PM on 30 May 2014.
	STC830 Location: NSW Member since 10 June 2010 Member #: 681 Postcount: 1256
The 05 is .05Mohm. The cap values should also have a decimal point - gets lost in the printing.

Return to top of page · Post #: 3 · Written at 8:29:13 PM on 30 May 2014.
	Brad Administrator Location: Naremburn, NSW Member since 15 November 2005 Member #: 1 Postcount: 7300
All those leading noughts are due to condenser values most often being expressed in microfarads rather than nanofarads and picofarads like they are today, for the smaller values. ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ A valve a day keeps the transistor away...

Return to top of page · Post #: 4 · Written at 8:42:47 PM on 30 May 2014.
	Airzone Location: Maclean, NSW Member since 30 May 2008 Member #: 291 Postcount: 341
OK guys thanks, just wanted to clarify. Peter

Return to top of page · Post #: 5 · Written at 9:51:39 PM on 30 May 2014.
	GTC Location: Sydney, NSW Member since 28 January 2011 Member #: 823 Postcount: 6686
Yep, it was usual to find cap values expressed as MF or MMF.

Return to top of page · Post #: 6 · Written at 10:03:42 PM on 30 May 2014.
	Marcc Location: Wangaratta, VIC Member since 21 February 2009 Member #: 438 Postcount: 5252
The big pain is that they invariably used no leading zeros before a dot that looked like fly excreta on the page. mfd: is micro Farad; mmf: micro micro Farad which is pico Farad aka pF. Several Mica types just had a number like 25 which is 25 pF. There are early circuits that, if you are familiar with radio, will spot, where all resistors like One hundred thousand ohms have 100M; not the modern 100K. "M" is 1000 in Roman numerals.

Return to top of page · Post #: 7 · Written at 6:34:46 AM on 31 May 2014.
	Scraps Location: Blue Mountains, NSW Member since 10 March 2013 Member #: 1312 Postcount: 401
100M? That's a trap for the unwary but would start you wondering about such a high value.

Return to top of page · Post #: 8 · Written at 9:39:54 AM on 31 May 2014.
	Simplex Location: Bathurst, NSW Member since 7 August 2008 Member #: 336 Postcount: 391
Some of those old resistor numbering system are rather bizarre at times, generally I measure them so as to be sure. Old faded or poorly copied circuits can be a nightmare.

Return to top of page · Post #: 9 · Written at 1:00:09 PM on 31 May 2014.
	MonochromeTV Location: Melbourne, VIC Member since 20 September 2011 Member #: 1009 Postcount: 1182
Just to add to the confusion some schematics from the 1920's & 1930's used the lower case Ω symbol, ω to denote resistor values.

Return to top of page · Post #: 10 · Written at 3:14:41 PM on 31 May 2014.
	Brad Administrator Location: Naremburn, NSW Member since 15 November 2005 Member #: 1 Postcount: 7300
Yeah, that is somewhat confusing - particularly to those who are not aware that the Greek alphabet has upper and lower case lettering and the style between the two looks very different unlike the Roman alphabet where most characters look similar between their upper and lower case versions. The Ω symbol here can be expressed by typing [ohm] though I never really considered adding the small letter. ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ A valve a day keeps the transistor away...

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