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I've recently been transliterating some old schematics for a friend of mine (Basically taking paper schematics from the 40s and drawing them in a modern EDA package) and have come across some very interesting/old electronics terms that are not in common parlance anymore.

Since I didn't know what they meant, I had to ask.

Therefore, I figure having a list of interesting/esoteric/old electronics terms would be useful, so here we are.

(Note: Try to stick to terms which were/are at least somewhat common, not things which you or someone you know thought up)


Please provide a short description for what the thing you are describing is, and a little historical info would be a positive. Just listing an Acronym or the name of an oddball instrument is not helpful if someone has encountered one of the things you are defining, and is trying to determine what it is/how it works.

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So "120Ω or to taste" is not acceptable? – tyblu Dec 24 '10 at 7:09
Since it doesn't have a specific definition, no. – Connor Wolf Dec 24 '10 at 7:12
Should probably be CW, but I can't seem to set it as such, even though I have moderator tools. – Connor Wolf Dec 24 '10 at 7:13
yeah, just flag it and we will come take care of it, thanks all the users whom flagged it for attention. There were many. – Kortuk Dec 24 '10 at 22:48

12 Answers 12


Some old drawings refer to capacitors as condensers.

I also seem to recall seeing diodes referred to as crystal rectifiers and/or crystal detectors - some packages still use CRxxx for diode reference designators, which is a nice historical nod.

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+1 for this! In some languages condenser and its derivatives are still used. – AndrejaKo Dec 24 '10 at 21:12
An even older term for capacitor is accumulator. – mgkrebbs Jun 20 '11 at 5:31
Be careful with "accumulator". In some parts of the world that used to refer to batteries. – Olin Lathrop Jun 23 '11 at 11:46
The funny thing is that in italian, "condensatore" is tipically used, while "capacitore" sounds archaic and weird – clabacchio May 25 '12 at 18:21
@clabacchio Still what I commonly see from my french associates. – Kortuk Dec 25 '12 at 16:15


Also known as Cycles per Second. It has basically entirely been displaced by the modern equivalent Hertz.

Commonly encountered in old texts. It was commonly used up until ~1960, when the SI officially replaced it.

You may also see kilocycle, megacycle and kilomegacycle, which are kilohertz, megahertz and gigahertz, respectively.


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Also known as micro-micro-Farads. It has basically entirely been displaced by the modern equivalent picoFarads

I encountered this in old schematics. Many capacitor values were noted as uuf

Specifically, since a pico is \$10^{-12}\$, and a micro is \$10^{-6}\$, a micro-micro is \$10^{-6}\cdot 10^{-6}\$, which equals \$10^{-12}\$.

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I've also come across several American schematics with no units for Henries or Farad; one must deduce the power, which is a pain. – tyblu Dec 24 '10 at 7:13
That even more fun! At least with resistors, it's generally assumed that no units means it's in ohms. – Connor Wolf Dec 24 '10 at 7:16
Also I've seen capacitors labeled 100MF - for 100 micro Farads – W5VO Dec 24 '10 at 7:42
@W5VO A lot of people seem to be blind for lower vs upper case, which is significant in units of measurement (another common mistake is using S for seconds). – starblue Dec 24 '10 at 8:32
It's remarkable how young much of the SI system is. Most of the electrical units are standardized only in 1948, the micro and pico prefixes and Hertz are from 1960. en.wikipedia.org/wiki/… – starblue Dec 24 '10 at 8:36

Having just gone through a ton of drawings for a rather old system I should know more of these. But what I can say so far:

1) Using the term 'return' instead of ground (although 'return' has in my mind a more specific connotation of being assigned to a specific signal rather than a general ground)

I'll keep editing this as I think of more.

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And don't forget 'earth' – Chris Stratton Feb 8 '11 at 5:25

Grid-Dip meter

Measures resonant frequency of RF circuits.

I was shown one once, but I wouldn't know how to use it.

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Is that possibly related to a SWR meter? – Toybuilder Jun 23 '11 at 5:21
A grid-dip meter used a vacuum tube oscillator controlled by an inductor and capacitor. The inductor was external and attached by a connector. This allowed 1) the inductor to be changed to get a range of frequencies, and 2) the inductor could be easily coupled to an RF circuit. When the resonant frequency of the RF circuit was close to the frequency of the grid-dip meter, it would cause the grid current to decrease. This dip would be seen on a meter (hence the name). More modern versions of a grid-dip meter use FET oscillators and thus the name was shortened to dip meter. – Barry Dec 25 '12 at 19:56

The differential operator "p"

In some older texts the variable "p" is used as a differential operator, where more modern texts the variable "s" is used, as with Laplace transforms. I think the "p" notation goes all the way back to the kind of operational derivative notation Oliver Heaviside introduced for solving differential equations. In some really old texts it seems that even more fundamental variables were not standardized; I was looking at an issue of the journal Nature from 1888 earlier which used the letter "C" for current instead of "I", and used "N" to represent flux instead of "\$\phi\$."

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RTL = Resistor-Transistor Logic
DTL = Diode-Transistor Logic

RTL was the first technology for logic ICs. Logical gates consisted of combinations of (surprise!) resistors and transistors.

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RTL was followed by DTL, which also included diodes.

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DTL, in turn, led to TTL, which was the last major technology based on BJTs. After TTL MOSFETs took over with CMOS in all its variants.

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Description/History please? – Connor Wolf Jun 23 '11 at 1:04
RTL can also mean Register Transfer Logic, which is an intermediate stage used by digital logic synthesis tools. – ajs410 Jun 24 '11 at 22:02
This is not history, I've studied that for my Bachelor. – Vladimir Cravero Dec 25 '12 at 19:22
The D-17B guidance computer, used in the Minuteman I missile, used a combination of DRL (diode-resistor logic), and DTL only where gain or inversion was necessary. The designers wanted to minimize the use of DTL because the reliability of transistors was a concern. The Apollo guidance computer on the other hand used only RTL (2800 IC's, all dual 3-input NOR gates). Both were designed in the early 1960's. I used surplus Minuteman II DTL IC's in my senior EE project in 1969. – tcrosley Nov 10 '14 at 18:26


I recently came across the "Barretter" which is a kind of iron-hydrogen resistor.

Still none the wiser? ... well neither was I. Essentially it is a gas-filled glass envelope containing a very fine wire. The wire has a positive temperature coefficient and a very low thermal mass. These devices were used to stabilize valve (vacuum tube) heater currents against variations in supply voltage.

In another form, the Barretter is so sensitive that it responds at audio frequencies to changes in the RF power of an AM signal, thus demodulating it. According to the Wikipedia article, the principle is still used in some microwave detectors.

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Mercury Cell

The mercury cell was technically one of the best primary cells ever: extremely long shelf life; nearly constant voltage over nearly its entire life and over a wide temperature range; etc. They were banned in Europe in 1991, and in the US a few years later.

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Description please? – Connor Wolf Jun 20 '11 at 0:57

Gate Expander

("RTL digital integrated circuit gate expander")

Back in the days of IC RTL (later replaced by DTL, then TTL, then dynamic NMOS, and so on) there were no single-chip 6-input NOR gates. If you needed an 6-input NOR, you took a normal 3-input NOR gate IC -- as used in the Apollo Guidance Computer -- plus a 3-input gate expander IC, and wired the outputs together ("wired-OR") to form an 6-input NOR gate. Here in the 21st century, most designers try (sometimes unsuccessfully) to prevent two outputs from getting connected.

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What does it do? It sounds like a 3-8 line decoder. – Connor Wolf Jun 20 '11 at 0:57
Were the outputs open-collector? Those can be ORed together by just connecting them together without any problems. – Connor Wolf Jun 23 '11 at 1:07
@Fake Name: Yes, gate expander outputs are open-collector. – davidcary Jun 26 '11 at 3:35

Cat's Whisker

Galena crystals were used as detectors in early radios since they behaved like diodes. However, one had to find the exact spot on the crystal to get the proper electrical performance. For this purpose, the crystal was placed in a holder and a stiff wire was mounted over the crystal with a means of adjusting the end of the wire over a spot on the crystal. When the right spot was found, the crystal radio would play. The wire became known as the cat's whisker.

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SSL or Solid-State Lamp

In some old circuits that I was looking at the other day, there were some that interfaced with "solid-state lamps". That's an old name for LEDs (light-emitting diodes).

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