Macdonald said:

Im a hobyest and I have a couple of questions.

I was looking for a .39 ohm 1 Watt Resistor. I went to 3 places which all

didnt have it. I guess I could mail order it but it seems kinda dumb for one

resistor.

So I bought a resistor that was 5 Watts .39 . at one place and then found a

2 Watt .39 Resistor at the other. My first question is since the circuit

calls for a 1 Watt resistor I suppose either one would work?

Its a very simple circut.

The second question relates to labeling of the resistors. The Bill for the

one resistor says 39R and the actual lettering on the OTHER resistor (5Watt)

resistor says R39.

I tested them with a meter and they both say 1.2 ohms on the 200 scale. Im

asuming that the meter just cant read the .39 so they really are .39.

Why does it seem that 39 (with no decimal point ) can stand for .39 . This

seems mis leading ??

Can anyone clarify this.

1) No problem with buying a higher wattage than you need, as long as

it fits in the circuit. Resistors are rated for maximum wattage -- how

much wattage they can take before they get too hot and fuse, burn, or

permanently change their resistance value. Any less than full power,

and they'll just be cooler. Higher wattage resistors are usually

physically bigger, though, so you should keep that in mind if space is

limited.

2) If your meter is OK, your 1.2 ohms might just be contact, wire and

probe resistance. But you should check to see that it's not measuring

on a higher range, because your two resistors almost certainly have

different values. The one that says R39 is 0.39 ohms, and the one that

says 39R is 39 ohms. Big difference, but if your ohmmeter is measuring

megohms, they both look like a short circuit. Check things out

carefully before you plug in the 39R one.

Here's how the euro method of labelling resistors works:

R39 0.39 ohms

3R9 3.9 ohms

39R 39 ohms

390R 390 ohms

3K9 3.9 Kohms

39K 39 Kohms

390K 390 Kohms

3M9 3.9 Megohms

and so on. If you see three digits, that usually means a 1 or 2

percent resistor. For instance, 3K92 would mean a 3.92K 1% or 2%

resistor. This isn't too difficult once you get the hang of it, and

it's a lot harder to miss a "K" on a print than a decimal point,

especially if it's a fourth generation Xerox.

Hope this has been of help.

Good luck

Chris