Resistors

[John99]

I am trying to repair a PCB and need to solder a 2.2K resistor (see pic).

http://www.positiveoffset.com/Parts/2.2K-ohm-resistor.jpg

Does this need to go in a specific direction or will it do the job no matter which direction it is facing?

[John99]

Any tips or links to electronic sites is also welcome.

[John99]

i just fried my laptop.

[leopold99]

I am trying to repair a PCB and need to solder a 2.2K resistor (see pic).

http://www.positiveoffset.com/Parts/2.2K-ohm-resistor.jpg

Does this need to go in a specific direction or will it do the job no matter which direction it is facing?
either way.
tip:
hold the resistor as close to the body as possible with needle nosed pliers to prevent the heat from damaging it.
after soldering, snip off the excess leads with diagonal cutters.

you can replace the old with the new one by crushing the body of the old one with pliers and then wrapping the leads of the new one around the pigtails of the old one.

[John99]

thanks. i just wanted to be sure but i made mistake by disconnecting the leads from a power supply and i did major damage. worst is a fried laptop. i am terrible with electronics. nothing ever works.

[cato]

that sucks. well, it's the perfect time of year to buy a new laptop

[MacGyver1968]

Let's see if I can remember my electronics school training...

Black, brown, red, orange, yellow, green, blue, violet, grey, white...

"Bad Boys Ravish Only Young Girls But Violet Gives Willingly" :)

[leopold99]

and to add to that:
the first two bands are the significant figures while the third band is the multiplier.
the fourth band is the tolerance.
if the first band is double wide then it's a wire wound resistor.

[thecollage]

what is inside of the resistor?

[MacGyver1968]

what is inside of the resistor?

Magic!

I think they are made of some sort of silicon. They sure smell nice when they fry. :)

[MacGyver1968]

and to add to that:
the first two bands are the significant figures while the third band is the multiplier.
the fourth band is the tolerance.
if the first band is double wide then it's a wire wound resistor.

Didn't know that part about the double wide part...I love learning stuff. :)

So in the resistor pictured, it has 3 red bands..Let's figure its value:

Red=2

So we have 2 as the first digit and 2 as the 2nd digit..with 2 zeros after...2200...so it's a 2.2kohm resistor! with a 5% tolerance. Fun fun...

Let's try another:

What would be a Brown, Black, Blue, Gold ?

[phlogistician]

I used to have a little chart I got free from Tandy (Radio Shack to our US cousins) back in the day, although after a short while, I started to remember the values.

In reply to MacG, 10MΩ, +/- 5%.

Hey, I found a cool chart like the one I used to have!

http://www.pc-control.co.uk/resistor_code.htm

[MacGyver1968]

This is one reason you will never find a colorblind electronic technician :)

[John99]

this looks like fun:
http://www.pc-control.co.uk/computrain.htm

i may try to fix the amp by changing the wires from the power switch to the pc board. i soldered thje resistor onto the back of the board but i dont think that was the problem. i did use a resistor with the same color coed: 3 red bands so i think i used the right one and i did smell something for a brief period after i flipped the ON switch but that could have been my imagination.

how do you know if a resistor is working or not?

[MacGyver1968]

how do you know if a resistor is working or not?

Use a voltmeter to read the voltage across the resistor. Failed resistors usually open up...instead of shorting.

If it's not black..and is connected to the circuit..it's probably working.

[John99]

Use a voltmeter to read the voltage across the resistor. Failed resistors usually open up...instead of shorting.

If it's not black..and is connected to the circuit..it's probably working.

I will take it apart again later to see what happened. When i use the voltmeter do i plug the amp into the wall?

This is a guitar amp and everywhere i read that messing around in there without bleeding the caps can be fatal so i would rather have it unplugged the whole time i am working in there.:D

i have a volt meter with red and black lead but there is a dial on it with numbers, any thoughts on what number to use?

To give you an idea:

ACV -
200V
500V

DCV-

DCA-

ah, i see now it has a selector for OHM. Guess that is the one to choose. My resistor is 2.2K.

[MacGyver1968]

Normally, you would take the voltage reading with the circuit hot...but with the voltages involved..I wouldn't chance it. Pull the resistor and check it with an ohm meter.

[John99]

a resistor alone will show up on the meter even if it is just sitting there?

[MacGyver1968]

On the ohm meter setting it will...the meter puts out a small voltage of its own so it can read the resistance. That setting only works on a non-hot system.

[leopold99]

Let's try another:

What would be a Brown, Black, Blue, Gold ?
resistors with a gold or silver tolerance band are precision resistors.
not really sure of the value though.

what is the tolerance if the 4th band is missing?

[MacGyver1968]

resistors with a gold or silver tolerance band are precision resistors.
not really sure of the value though.

what is the tolerance if the 4th band is missing?


Gold is 5%, and silver is 10%...not sure about no band...how would you tell which is the first band, if there wasn't a tolerance band?

[Read-Only]

Magic!

I think they are made of some sort of silicon. They sure smell nice when they fry. :)

Hi, Mac,

It's just compressed carbon. Except for the precision ones which are wirewound.

[MacGyver1968]

Hi, Mac,

It's just compressed carbon. Except for the precision ones which are wirewound.

You're always full of useful information RO!

I get wirewound when I drink too much strong coffee. :)

[leopold99]

Gold is 5%, and silver is 10%...not sure about no band...how would you tell which is the first band, if there wasn't a tolerance band?
answer 20%

the bands are grouped at one end.

[MacGyver1968]

resistors with a gold or silver tolerance band are precision resistors.
not really sure of the value though.

what is the tolerance if the 4th band is missing?

Ok..

Brown is 1

Black is 0

Blue is 6

First digit is 1...second digit is 0, with 6 zeros behind it.

so it would be 10,000,000 ohms or 10 Mohm.

Come to think of it, you always have a tolerance band or you wouldn't know which way to read the bands.

[MacGyver1968]

nm...i was posting while you answered. I done learned me somethin' else :)

Maybe some lurkers learned to read color codes on resistors. :)

[leopold99]

so it would be 10,000,000 ohms or 10 Mohm.

the "ohm" part can be dispensed with and you use just the M instead.
10M is 10 megohm.
10K is 10 kilohm.

[Read-Only]

You're always full of useful information RO!

I get wirewound when I drink too much strong coffee. :)

:D:D

[MacGyver1968]

the "ohm" part can be dispensed with and you use just the M instead.
10M is 10 megohm.
10K is 10 kilohm.

For the purpose of this thread, yes...since we're only talking about resistors. But in proper electronic notations, M only means mega.. you need a unit, to tell what your talking about...and I don't know how to make an "omega" symbol on the keyboard to indicate ohms. :)

[leopold99]

For the purpose of this thread, yes...since we're only talking about resistors. But in proper electronic notations, M only means mega.. you need a unit, to tell what your talking about...and I don't know how to make an "omega" symbol on the keyboard to indicate ohms. :)
yeah, i see your point.

another question for you.
the transconductance of a vacuum tube is the same as beta of a transistor.
what greek letter represents transconductance?

[MacGyver1968]

Not sure...we didn't discuss vacuum tubes when I was in electronics school back in '94. I only have a two-year degree..so my knowledge is rather basic...and getting rusty. :) That's kinda one reason I've been trying to participate in these electronic threads..so I can refresh knowledge that I'm starting to lose due to time.

What's the symbol?, and could you give a brief explanation of transconductance?

[leopold99]

mu.

transconductance is essentially the current flow through the tube at a given grid voltage.
edit:
For vacuum tubes, transconductance is defined as the change in the plate(anode)/cathode current divided by the corresponding change in the grid/cathode voltage, with a constant plate(anode)/cathode voltage. Typical values of gm for a small-signal vacuum tube are 1 to 10 millisiemens.
- from wikipedia
end edit

the naming of vacuum tubes are systematic.
diode, two elements, plate cathode.
triode, 3 elements, plate grid cathode.
tetrode, 4 elements, plate 2 grids cathode.
pentode, 5 elements, plate 3 grids cathode.
the naming for the grids starting from the cathode are:
control
screen
suppressor
note that the heater is not an element unless it is the cathode itself.

[John99]

There is a power switch with four wires. What i did was change two wires, one white and one black and now the amp works good as new.

Anyone know what the significance of the colored wires is? What about positive = RED and negative = BLACK? Why is the sometimes a white wire and a red wire? And how come one of those is positive?

[leopold99]

Anyone know what the significance of the colored wires is? What about positive = RED and negative = BLACK? Why is the sometimes a white wire and a red wire? And how come one of those is positive?
the significance of colored wires is to make it easier to troubleshoot the circuit and to a lesser extent to tell what kind of voltage is on the wire.
in most circuits red does indicate positive and black indicates ground.
believe it or not, in AC circuits the white wire is ground while the black is hot (unless this has changed in the last few years)
except for the AC circuits mentioned above there is no code for wire colors.

[John99]

the significance of colored wires is to make it easier to troubleshoot the circuit and to a lesser extent to tell what kind of voltage is on the wire.
in most circuits red does indicate positive and black indicates ground.
believe it or not, in AC circuits the white wire is ground while the black is hot (unless this has changed in the last few years)
except for the AC circuits mentioned above there is no code for wire colors.

Thanks. That is what i wanted to know.

[orcot]

http://www.geocities.com/aliciainelpaso/schematics/resistor-color-code.gif

[MacGyver1968]

and now the amp works good as new.



Bad ass! Way to go! Rock on my brother! :)