I recall that electrolytic caps used to always be numbered with even numbers. 50uf for example. Now, that would be a 47uf cap. WHY? Do they save a few cents by making it a tiny bit lower in capacity, or what?
"50" was never a "standard"
... 43 47 51 56 ... is ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
I recall woking on many table radios in the 1960s that used 50C5 and
35W4 tubes and most of them had dual filter 'lytic caps that were 30uf and 50uf (in the same package). Some also had a 3rd one at about 10uf in that package. These were under the chassis and were the wax coated paper ones.Most of the old tube tv sets had the aluminum cans, and they too were labelled 50uf, 80uf, 20uf, etc......
(I'm talking tube equipment here).
Same reason why we don't have 3 dollar bills.
We had to limit the number of items to stock. Overtime, these are the more popular values:
22 33 47 56 68 74 84 91, etc.
I'd think it highly unlikely that cost saving is the reason. The saving is probably insignificant anyway. It's almost certain that manufacturers decided to go with the equal ratio sequence as with resistors.
They tightened the specification.
Those old 30 µF electrolytics often fell outside the +100%/-20% spec.
-- You can't have a sense of humor, if you have no sense.
So, Mr. Van Winkle, how was the nap?
Caps have been sold with the standard E6 or E12 preferred number system for as long as I can remember, and my #1 son is taking college classes.
-- www.wescottdesign.com
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Then the next question is why we have these values for resistors. In fact, if we have a different sequences for R, C and L, we would not have to say R22 and C22. Perhaps 22 for R, 23 for C and 24 for L.
Yup, that's the reason. I was gonna say though that it's the new capacitor tax :-)
With dog food, OTOH, it's a whole different game. "We kept the prices stable" and blah .. blah. Took a closer look at the bag, contents went from 35lbs to 30lbs. Yoghurt pots now tend to have a false bottom. Looking underneath one can often see that the bottom is almost 1/2" recessed so the beker looks larger while it sits on the shelf. So far for that nonsense of "There is no inflation". Hurumph!
-- Regards, Joerg http://www.analogconsultants.com/
These values are the result of dividing a decade into a number of values where any two adjacent values have the same ratio, the resulting values being rounded off to 2 or 3 significant digits.
In the E12 series, the values are 10, 12, 15, 18, 22, 27, 33, 39,
47, 56, 68, 82. Each value is approximately 1.2115 times the one preceding it, rounded off to the nearest two digits. 1.2115..... is the twelfth root of 10. In the E96 series, often used for 1% resistors, the ratio is the 96th root of 10 which is 1.024275....... which is why we have odd values like 332 ohms, 6.81k, etc.
Some of us old farts were into this stuff long ago - and for one reason or another, had to stop for a few decades. Doesn't make us all bad...
-- Leave no stone unturned. -- Euripides
If you were still used to capacitance being stated in centimeters you qualify for membership in the ROF group (Really Old Farts) :-)
-- Regards, Joerg http://www.analogconsultants.com/
That's exactly what I did, and now I'm back into it, in my retirement days. The only problem is that I still prefer working with tubes. Semiconductors just dont have the "excitement" for me and can be a major PITA to test, and to get parts. Point to point wiring is so much easier to work on too, compared to printed boards.
The only advantage to transistors is that the voltage wont throw a person 30 feet across the basement, which happened to me when I was about 17 years old. (1000VDC supply with RF backing up due to no dummy load on a tranmitter, and I hit the bare cap of the output tube). [I recited all 27 cuss words in under 5 seconds that day] :)
(Yea, I bought an insulated tube cap the next day).
I'm pretty sure they went over to the E6/E12 preferred numbers about the same time they changed from tubes to transistors.
-- www.wescottdesign.com
They did? where was I when that happened? :)
Actually, tomorrow I must service some lab equipment "Dielectric tester" that still has selenium rectifiers in it, operating the clutch on the variac, armature and field for the motor..
Sounds like fun. Must track down a short that is generating some nice arc flashes in the motor drive circuit!
P.S.
You would think as big as we are, they would of upgraded long ago!
We are the original "Brand Rex" company, the one that created the first cross link compounds (irradiation process), etc..
Btw, we still have the very first process RDI (Irradiation) unit ever made world wide still in operation. There was one made before that but was for the air force, placed in their care somewhere.
Jamie
'Twas in cm in my undergraduate education. A lot of physics is still done in Gaussian units because it makes the algebra a lot easier.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Thankfully, that was before my time. The only centimeter stuff I had was the cgs system in physics. I've long since forgotten most of that, since there aren't many people who speak physics (or weren't, until the Internet came around).
-- Those of you who think you know everything are annoying those of us who do.
I often ask for those at the bank, along with other prime number denominations, just for kicks.
-- _____________________ Mr.CRC crobcBOGUS@REMOVETHISsbcglobal.net SuSE 10.3 Linux 2.6.22.17
1-2-5 sequence make a lot of sense (cents?) for money and trimpots. Eg. $10/$20/$50/$100 (and eventually we'll probably see $200/$500/$1000 so you don't have to use a wad of cash to pay for a big mac.
It actually started just prior to WWII. The military electronics manufacturers were giving away their radios in turn for a lock on the spare parts thing (google Henry Ford and spare parts). The old thousand dollar toilet seat on a military aircraft syndrome. Ten dollar half-watt resistors of a "special" value with a single source.
The military told the RMA (Radio Manufacturer's Association, since morphed into RETMA - Radio Electronics Television Manufacturer's Association) to come up with a set of standard values and they came up with the 20%, 10%, and 5% tolerance values (calculated as fractional powers of 10) for components and the JAN (joint army navy) scheme for vacuum tubes. Resistor manufacturers, tube manufacturers, and nearly everybody else but capacitor manufacturers came on board quickly. It is only in the last few years that we've come to be using RETMA standard values for capacitors.
Jim
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