Resistor codes? Which way round?

chillidoggy

Looking at resistor colour codes, which end do you start reading from? If I go and build an amp, it's dawned on me that it would be a really helpful piece of knowledge.

digitalscream

As I recall, the gold or silver band goes on the right (gold = 5% tolerance, silver = 10% tolerance), then read the others from the left.

If the code is lopsided, put the end with no band on it to the right - that indicates 20% tolerance.

crunchman

Others will probably know more than me but I think there is normally a bit of a gap to the last band denoting the tolerance.

I always play it safe and cheat by checking the value with my multimeter.

randomhandclaps

The gap should be to the right.

ecc83

"Once upon a time" resistor values were as an open book to me. I could read them at a glance.

Then! They brought in this 4 band system and of course made the resistors ever wee'er. So, a combination of failing eyesight and failing brain means that I just get out my trusty Fluke 83 and check 'em before I use 'em!

"Funny" story. Not to do with colour codes per se but certainly how to feck up production big time....

A factory I worked at for 10 years made network modules of all sorts and two of them had resistors in them. The telephone master module 1meg and another called the "ISDN" module that had 100R termination resistors. In the stores there were two open bins side by side each containing 10,000 of each value, stripped off their bandoleers.

I leave you to guess what happened!

Dave.

Jaden

bigger
better
resistors
or
your
grid
bias
voltage
goes
west

thats the colours remembered

Rocker

http://www.dannyg.com/examples/res2/resistor.htm

There are many such on-line resistor colour codes calculators.

thermionic

I made one of these - very useful!

ChrisMusic

thermionic said:    I made one of these - very useful!

That is such a good idea  

chillidoggy

Good stuff! Now the only problem is that some of the colour bands are not exactly distinct on some resistors.

crunchman

Only problem with the wheel is if you get a resistor with more rings on it.  I printed off a copy of this:

ICBM

Once you get familiar with them it's usually fairly easy to work them out - there are only certain combinations of the first two stripes normally, since the standardised values are a specific set… which look odd to human 'logic' at first, but are actually equally spaced from a percentage tolerance point of view.

10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and multiples thereof are the "E12" or 10% tolerance set, and the "E6" values (every other one from that series) are by far the most common. There are also "E24" values, and even finer multiples which are used rarely.

The ones that can be most difficult are red and orange, and sometimes (when it's the multiplier, usually) there's no way to be certain other than to measure them.

chillidoggy

And presumably you have to de-solder them to measure the resistance value? Here's an example of what I mean about the colours being indistinct. Is that brown, red or orange on the two grey bodied ones? And it looks like a cross between purple, mauve and red on the one on the left!

http://i232.photobucket.com/albums/ee189/chillidoggy/DSCN1445a_zps592327a3.jpg

ICBM

The left one is brown/black/orange (10k) and the right one is yellow/purple/red (4K7) - comparing the two helps to distinguish the red and orange, and some familiarity with typical circuit values helps as well - that's only going to come with experience, but like anything else it does get easier. Since that's a standard HT chain, the right one isn't going to be 47K (the only other possibility), although the left one could possibly be 1K - but not when you compare it to the 4K7. As usual, the '10' (brown/black) and '47' (yellow/purple) pairs are standard values and make it clear which those are.

You don't usually have to desolder them to measure the value - although they will probably take some time to stabilise on the meter if there are large caps attached, which will need to be charged to the meter's testing voltage. Valve amps are normally AC-coupled (ie have capacitors which block the steady metering current) between stages so you will normally be able to get readings in situ - they might be very slightly wrong but will usually allow you to confirm the codes and tell which order of ten you're dealing with. Solid-state amps can be a different thing entirely though - they're usually DC-coupled which means that just metering parts in situ can produce very confusing results!

chillidoggy

Much obliged!

Given the weather forecast for the weekend, I can feel a resistor-code familiarisation with a multi-meter session coming on. I've noticed that some resistor codes are more easily readable than others, and like you said, it will come with experience.

Mind you, you know what they say about a little bit of knowledge!

ecc83

Re measuring resistors in situ. Make dead bang certain that ALL residual voltage has been drained! Even a few tens of volts can fork a cheap DMM. 

Resistors almost never go low, at least not the commonly found metal film types. In fact MF hardly ever go wrong at all! I have only had one instance of an R going high in 5 years and that was a 1meg in a PSU feedback path. I have had bias and grid stoppers gone black from a valve flashover but when measured they were within 5% of correct value. (they were of course replaced anyway!). 

There are of course still amps being made with carbon comps in them for "audiophool" reasons and these can go up,down, sideways and noisy!

Dave.

Cirrus

ecc83 said:

There are of course still amps being made with carbon comps in them for "audiophool" reasons and these can go up,down, sideways and noisy!

Dave.

I've heard it said that when there's significant voltage across them they do something to the sound, but in other places they're totally pointless - all they'll do is add noise, drift with heat and age etc. They sure do look pretty though.

:>

ICBM

Cirrus said:

ecc83 said:

There are of course still amps being made with carbon comps in them for "audiophool" reasons and these can go up,down, sideways and noisy!

I've heard it said that when there's significant voltage across them they do something to the sound, but in other places they're totally pointless - all they'll do is add noise, drift with heat and age etc. They sure do look pretty though.

Yes, I think carbon-comps can make an audible difference in locations where they have high signal voltages on them - plate resistors mainly or exclusively. In other places they make no difference and in anything where fairly high power is developed (or even where they just get hot from another source) they're a liability.

Caps likewise - if there's high signal AC on them they do affect the sound, otherwise not.

chillidoggy

ecc83 said:

Re measuring resistors in situ. Make dead bang certain that ALL residual voltage has been drained! Even a few tens of volts can fork a cheap DMM. 

Resistors almost never go low, at least not the commonly found metal film types. In fact MF hardly ever go wrong at all! I have only had one instance of an R going high in 5 years and that was a 1meg in a PSU feedback path. I have had bias and grid stoppers gone black from a valve flashover but when measured they were within 5% of correct value. (they were of course replaced anyway!). 

There are of course still amps being made with carbon comps in them for "audiophool" reasons and these can go up,down, sideways and noisy!

Dave.

Can you translate that into English, Dave?

ecc83

chillidoggy said:

ecc83 said:

Re measuring resistors in situ. Make dead bang certain that ALL residual voltage has been drained! Even a few tens of volts can fork a cheap DMM. 

Resistors almost never go low, at least not the commonly found metal film types. In fact MF hardly ever go wrong at all! I have only had one instance of an R going high in 5 years and that was a 1meg in a PSU feedback path. I have had bias and grid stoppers gone black from a valve flashover but when measured they were within 5% of correct value. (they were of course replaced anyway!). 

There are of course still amps being made with carbon comps in them for "audiophool" reasons and these can go up,down, sideways and noisy!

Dave.

Can you translate that into English, Dave?

Which part did you not understand Chuck?

Dave.

chillidoggy

DMM

Resistors going low

MF

PSU feedback path

Bias and grid stoppers

Valve flashover

Carbon comps going up down and sideways

Apart from that I was fine, Dave!