View Full Version : General question about old 'condensors' (capacitors)


Wigwam Jones
12-24-2011, 12:10 PM
I'm reading some old tube amp schematics, and I notice that the parts lists give values like this:

C-1: .05 mfd 400v paper cond.
C-2: 10 mfd 25v elec. cond.

And so on.

On the schematic itself, C-1 does not have + or - symbols indicating polarity, but C-2 has both + and - noted. This is consistent throughout the schematic and parts list.

So just to make sure I understand, can someone help shed some light on this conversion from older to modern terminology?

'cond' means capacitor, right?

'mfd' means uf, right? So .05 mfd is the same as .05 uf?

And when the parts list specifies 'paper cond.', and no polarity listed, what kind of modern-day capacitor is it referring to? The only non-polarity capacitors I am aware of are electrolytic NP or the more modern poly style which I presume did not exist then. So I'm a bit confused here.

Is an 'elec. cond.' actually an electrolytic capacitor?

Thanks!

Pandovski
12-24-2011, 12:17 PM
You got all those terms right.

Wikipedia:
"Electrolytic capacitors are capable of providing the highest capacitance values of any type of capacitor (see Supercapacitors)[citation needed] but they have drawbacks which limit their use. The standard design requires that the applied voltage must be polarized; one specified terminal must always have positive potential with respect to the other. Therefore they cannot be used with AC signals without a DC polarizing bias. However there are special non-polarized electrolytic capacitors for AC use which do not require a DC bias. Electrolytic capacitors also have relatively low breakdown voltage, higher leakage current and inductance, poorer tolerances and temperature range, and shorter lifetimes compared to other types of capacitors."

http://en.wikipedia.org/wiki/Electrolytic_capacitor#Types

nashvillebill
12-24-2011, 12:29 PM
Paper caps are very old and actually consisted of wax-impregnated paper. They were sort of a precursor to film caps. Replace them!!

Here's a better explanation of old-style caps http://antiqueradio.org/recap.htm

Sam Cogley
12-24-2011, 12:30 PM
I'm reading some old tube amp schematics, and I notice that the parts lists give values like this:

C-1: .05 mfd 400v paper cond.
C-2: 10 mfd 25v elec. cond.

And so on.

On the schematic itself, C-1 does not have + or - symbols indicating polarity, but C-2 has both + and - noted. This is consistent throughout the schematic and parts list.

So just to make sure I understand, can someone help shed some light on this conversion from older to modern terminology?

'cond' means capacitor, right?

'mfd' means uf, right? So .05 mfd is the same as .05 uf?

And when the parts list specifies 'paper cond.', and no polarity listed, what kind of modern-day capacitor is it referring to? The only non-polarity capacitors I am aware of are electrolytic NP or the more modern poly style which I presume did not exist then. So I'm a bit confused here.

Is an 'elec. cond.' actually an electrolytic capacitor?

Thanks!

A paper cap in that application is going to be equivalent to a non-polarized film or paper/oil capacitor.

mfd is the old designation for what is now listed as uF.

Condenser was a very old term for capacitor.

Elec., as you have surmised, is electrolytic. Replace with a good modern electrolytic like Nichicon or Panasonic.

kirk57
12-24-2011, 12:37 PM
and if anybody is wondering or cares, the u is used for the greek letter mu (for micro), which when written looks a lot like a u on English keyboards.

Wigwam Jones
12-24-2011, 12:38 PM
Thanks, all! I should have said, there is no amplifier. I am just reading a schematic and trying to make sure I understand it (mechanically and electrically, I can't claim to understand the electronics themselves yet).

Specifically, I was reading "Practical Amplifier Diagrams," by Jack Robin and Chester Lipman, 1947, and looking at the simplest amplifier diagram they have, a 1-watt amp based on a 117N7GT tube. It has a hot chassis design, but I suspect that one could build this as a first tube-building experiment if one used an inexpensive isolation transformer and a fuse. So I'm just trying to make sense of it all. Thanks again!

mightynutmeg
12-25-2011, 12:16 AM
and if anybody is wondering or cares, the u is used for the greek letter mu (for micro), which when written looks a lot like a u on English keyboards.

hold option to get special characters... option+m=

at least if you are on a mac
Somebody told me, for a PC you have to hold down alt and type in the unicode value... I could never figure that out and always pull up "character map" on the PCs at school.

cademan
12-25-2011, 12:55 AM
Just go to the web and get a list of ALT codes for PC users. ALT234 is the greek omega (ohms) symbol. Ω

Pandovski
12-25-2011, 01:00 AM
A good read about capacitors, tests and reviews.

http://www.humblehomemadehifi.com/Cap.html

Where I live in this part of Europe everyone professionally still names capacitors as condensers.

Hyperion
12-25-2011, 06:31 AM
Just go to the web and get a list of ALT codes for PC users. ALT234 is the greek omega (ohms) symbol. Ω

And ALT 230 is the code for = micro :yes: :smoke: