Lesson R,L,C,T,V,D but Q and U ?

[JacKam_]

After over 40 years of tinkering I asked myself why Transistors on PCBs and circuit diagrams have often prefix "Q".

"L" stands for Lentz. It is easier to read L112 than I112.

"U" for ICs is "unspecified" or "unrepairable" [Althought I always thought it is from "Uklad scalony" (Pol) == "integrated circuit" (Eng)]
But I am not sure.

Regarding Transistors, I found the picture below, is that all ?

J

[paulsherwin]

I don't know why the Q convention for transistors was adopted. It certainly predates the TO5 encapsulation. They were originally known as 'crystal triodes', but C was obviously already in use for capacitors. Does anybody know why T wasn't adopted?

[kalee20]

I've seen VT on some circuit diagrams for transistors.

Interestingly, older Practical Wireless magazines used TR for transformers (before transistors). But in the 1970's, Everyday Electronics used TR for transistors and just T for transformers.

I have used Q for transistors certainly since 1989 in the day job! I may have used TR before then... have to look out an old PCB and check the legend!

[Herald1360]

I reckon U for ICs is just a variation on μ (for μcircuit or microcircuit) corrupted further by being uppercase since uppercase μ is M which would really confuse things (megacircuit anyone?).

Perhaps LSI chips should be megacircuits?

VT I always thought was Valve Transistor, though TR could derive either from TRansistor or Transfer Resistor which was where transistor came from in the first place.

As long as the symbols are recognizable- not easy in some circuits either, the various prefixes used are at least cross referenced.

[TonyDuell]

And I (probably incorrectly) thought that 'U' meant 'Unit' (as in a circuit made as a single unit). DEC used 'E' for IC's on their diagrams and PCBs, I do not know what it stood for.

I've seen signal diodes labelled 'CR' (Crystal Rectifier I guess) and power diodes 'MR' (Metal Rectifier), even when they were silicon junction types.

[G6Tanuki]

In WWII-era parlance "VT" was "Valve, Transmitting" [and VR was "Valve, Receiving].

Must admit, as time went on and transistors proliferated, I really liked the Dutch "ELEKTOR" magazine's approach to "use whatever generic device you have here, it's not at all critical" .

TUP - Transistor, Universal PNP
TUN - Transistor, Universal, NPN
DUG - Diode, Universal, Germanium
DUS - Diode, Universal. Silicon.

of course by the 1980s a "generic" small-signal silicon transistor had a Ft and UHF noise-figure which people could only have dreamed-of in the 1960s.

[This sometimes causes problems: designers of audio amps in the 1960s assumed the devices they specified had sod-all VHF/UHF gain; which was fine until someone replaced an old 'anything above audio-frequencies is a bit of a strain' transistor with a 'modern' amplifies-DC-to-light equivalent and suddenly found they were receiving police/taxi VHF two-way radio transmissions].

[G6Tanuki]

Originally Posted by Herald1360

I reckon U for ICs is just a variation on μ (for μcircuit or microcircuit) corrupted further by being uppercase since uppercase μ is M which would really confuse things (megacircuit anyone?).

Fairchild's first rather-simple ICs were called the "Micrologic" series and the marketing blurbs of the era interchanged μ and U wantonly.

I've got a few μL914 chips here - what can you actually *do* with two long-tailed-pairs?

[Andrew B]

I think the "Q" stands for "quick blow fuse" ?

[MrBungle]

Transistors certainly make good quick blow fuses

[TonyDuell]

Originally Posted by G6Tanuki

In WWII-era parlance "VT" was "Valve, Transmitting" [and VR was "Valve, Receiving].

Must admit, as time went on and transistors proliferated, I really liked the Dutch "ELEKTOR" magazine's approach to "use whatever generic device you have here, it's not at all critical" .

TUP - Transistor, Universal PNP
TUN - Transistor, Universal, NPN
DUG - Diode, Universal, Germanium
DUS - Diode, Universal. Silicon.

Although I seem to remember that the American military used 'VT' (standing for 'Vacuum Tube') for all their valve numbers. This caused some nasty confusion where it was least needed.

I liked the Elektor system too. In a lot of cases (as I am sure many of us know) the reason that a particular transistor or diode was used in the prototype of a magazine project was that it was what the designer had on the bench/in the junk box. I am guilty of that too. I'll send out a circuit with a 2N3904 transistor on it. Most likely a BC547 would work just as well, but the 2N3904 is what I have in stock.

I seem to remember reading an article in one of the magazines in the 1970s where the author (correctly in my opinion) stated that most circuits could be built using only 5 types of transistor :

A small-signal NPN (2N3904)
A small-signal PNP (2N3906)
A medum power NPN (BFY50)
A power NPN (2N3055)
An n-channel FET (2N3819).

Obviously there are exceptions, but it's surprising what you can do with just those types).

[julie_m]

Transistors make terrible fuses. A fuse is supposed to fail open-circuit!

[TonyDuell]

There is a commonly-given corollary of Murphy's Law :

'A transistor protected by a fast-acting fuse will protect the fuse by blowing first'

My experience though suggests :

'A transistor protected by an expensive very-fast fuse will first fail short-circuit, ensuring the fuse fails too'

[Herald1360]

Originally Posted by julie_m

Transistors make terrible fuses. A fuse is supposed to fail open-circuit!

As long as there's no real fuse involved, the short circuit state in anything but low powered battery kit is usually followed by the open circuit one when the bond wires turn into fuses. A complementary pair may end up as one open one short.

[G4YVM David]

Could q come from the German Quelle, "source"?

I've found several reasons online, the most believable one according to Occam's razor is that the letter Q was simply the next in line unused one!

D

[Synchrodyne]

The use of “Q” to identify transistors in schematics appears to have been common in American practice and from a very superficial search, it may be dated back to 1959 January at least, although I’d guess that it originated before then. A deeper search of the late 1950s American magazines at: http://www.americanradiohistory.com/ might reveal its origins.

In the UK, “Wireless World” (WW) magazine was using “Vt” in the early 1960s, as for the 1961 and 1965 versions of the Dinsdale amplifier. By the time of the Bailey amplifier in late 1966, it had changed to “Tr”. I’d guess that the reasons for that change could well have been provided in the pages of the magazine somewhere during 1966. WW evidently stayed with “Tr” at least through 1998, that being used in the Slifkin & Dory Synchrodyne/Homodyne article of that year.

Amongst the UK equipment makers, the situation looks to have been rather entropic. Here is a small and random sampling from the data readily to hand:

Eddystone started with “TR” for its 960 receiver of 1962, and stayed with that at least until its 1650 of 1984.

Leak used “T” for its early solid-state amplifiers (Stereo 30, Stereo 70, Stereo 30 Plus) but then switched to “VT” for its 1969 Stereofetic FM tuner. But perhaps surprisingly, it had used “Q” for the stereo decoder section of its Troughline Stereo tuner.

Rogers used “T” for the first edition of its Ravensbourne amplifier (“TR” was used for the transformers, including the quadrifilar driver), but then changed to “VT” for the first editions of its Ravensbourne 2 FET FM tuner and its Ravensbrook amplifier. The Series II version of the Ravensbourne tuner used a mix of “T” and “VT”. I don’t know what it used for its MPX decoder, which was its first solid-state product. In the case of the first Ravensbourne tuner, the Fairchild µA703 ICs were also labelled as “VT”. The Ravensbrook FET FM tuner used “TT” for RF transistors (and fets) and “TA” for decoder/AF transistors, but its RCA ICs did not have letter labels.

Quad started with “Tr” for its MPX decoder of 1963, and stayed with that (or “TR”) until 1982, when the Quad 34 and FM4 both used “T”.

Sugden used “VT” for its early equipment (A21, C51/A51 and R21/R51).

Racal used “VT” for the RA1217, but “TR” for the RA1772, and then “Q” for the RA1972.

Marconi used “TR” for the Apollo (1970) but “Q” for the Oceanic (c.1984).

GEC used “VT” for the RC410-R, as did Plessey for the PR155, then “TR” for the PR2250.

From that one might deduce that “VT” (or “Vt”) was popular amongst the UK makers in the 1960s, with a swing to “TR” (or “Tr”) coming later in that decade. The earliest I have for “TR” right now is for the Jason FMT4 tuner of 1960, which used a solitary transistor as part of its amplified afc system. But a deeper search would likely reveal earlier examples.


Cheers,

[Synchrodyne]

I also had a quick look at Sony practice, as probably representative of Japan Inc. It seems to have changed from “X” to “Q” somewhere in the mid-1960s. The CV-2000 video recorder used “X”. But the transistor monitor interface in the CVM-2300U domestic receiver-monitor (of c.1965) used “Q”, as did the TUM-100 outboard TV tuner, which was intended to be used with the CV-2000.


Cheers,

[Argus25]

Originally Posted by TonyDuell

And I (probably incorrectly) thought that 'U' meant 'Unit' (as in a circuit made as a single unit).

I'm pretty certain this is correct I have seen parts list for circuits that say "unit" when the IC's are labelled prefix U on the schematic.

[Argus25]

Originally Posted by julie_m

Transistors make terrible fuses. A fuse is supposed to fail open-circuit!

I have a mid 1980s' vintage Hero Jnr robot (made by Heathkit) It uses the amazing speech speech synthesizer IC, The Votrax SC01A. It comes with a number of pre-programmed words of wisdom. One of them is:

"Smoking transistors is hazardous to my health"

one other : "I have the utmost confidence in this mission Dave"

[Synchrodyne]

From further searching, one may get back at least to 1956 with “Q”. Electronics magazine for 1956 September carried the article on the Lin quasi-complementary amplifier circuit, and this used Q1, Q2, etc., for the transistors. Going back to say 1953 one finds some circuits with the transistors labelled as “jT”, presumably for “junction transistor”. Terman 4th edition (1955) used “T”.

Popular Electronics magazine changed to “Q” from its 1958 December issue. In 1958 November and previously it had used “TR”. At that time Radio-Electronics magazine was using “V”. It appeared to have changed to “Q” by the end of 1962.

Given that Lin was an early user of Q, it could have been an RCA idea, which at least provides another search vector in the quest for its origin.

Cheers,

[Mad Mal]

Later convention for Transformers was to use Tx or TX... As in LOPTx (line output transformer). It was to distinguish from any other inductance which used the L as a marker prefix. (That said some early German diagrams had all inductance units marked with a W the link being the unit of measure the Weber)
I have confusingly also seen a coil with a dust core given an I prefix on a French CCt diagram And some Toshiba transistors in a radio circuit prefixed with an S, what's going on there?