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 Post subject: Reisstor bands
PostPosted: May Tue 25, 2021 10:23 am 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 141
Location: Athens, Greece
Hi there,
Can someone tell me what the bands in this resistor are? I see red, black, gold but I am not sure. It measures 24.7 Ohms and if my vision is correct, that reading is off.


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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 11:40 am 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 1081
Location: Stone Mountain, GA
Hard to see in picture from far away. But looks like red red black gold or 22 ohm 5%.

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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 11:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6617
Location: Montvale NJ, 07645
Definitely need a better close up picture in good natural light.


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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 12:15 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 141
Location: Athens, Greece
That's because I could not find the proper setting in my camera.
I am attaching two good pics and a resistors color table in which the bottom line shows red-black-gold.
I thought that if that was red-black-gold, the value should be 20 Ohms but according to the table the gold means a multiplier of 0.1 which would mean the 20 becomes 2.0. Any clarification?
However, even if it were 20 with a 5% leeway, the measured value of 24.7 should indicate the resistor is gone, correct? It is connected by the way to a zener diode in a transfromer/stepdown of 220VAC/9VDC.


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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 12:20 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 141
Location: Athens, Greece
Hi Scott,
So you are in peaceful Montvale and most likely we crossed paths in some ham fest when I lived in NJ.


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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 12:43 pm 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 1081
Location: Stone Mountain, GA
Yes, Red Red Black Gold: 22 ohms, 5%

Yes, 11% off but probably still works.

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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 1:36 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 10879
Location: Long Island NY
If you want to measure a low value resistor like this accurately you have to subtract the lead resistance when using a DMM. With VOMs and VTVMs this is taken care of when you zero the meter out, but most DMMs don't have the means to do this.

If you have a DMM, short the probes together and note the reading. You will probably get a number around 0.7 ohms. Some will be a little higher, some a little less. That number is to be subtracted from whatever it reads when you measure the resistor. So your 24.7 ohm resistor is probably more like 24 ohms. 24/22 = 9% over marked value. The gold band means 5% tolerance, so technically it is out of spec but not so far out that it should cause the circuit you describe to malfunction. Resistor values only hold when measured at a specific temperature, nominally 25 degrees C (77 degrees F) so if the temperature was different--say you just unsoldered it and it was still considerably hotter than room temperature when you measured it--then it could read higher.

If the resistor is in series with a Zener diode in a power supply circuit of some kind, a couple more ohms might actually be advantageous, since that would tend to lower the current through the diode, helping it to last longer.

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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 5:40 pm 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 141
Location: Athens, Greece
Thanks, I will try to measure it with two more meters but how does the multiplier works because if we multiply 20 by 0.1 for gold we get 2.0 Ohms.
On a related issue, I have to replace two axial electrolytics ( which was the reason I got curious about the resistor), one is 470/10, the other 2000/18 but I can not find axials here so I have to go with radials. That poses a problem because the large cap goes sideways on the back of the board and measures an inch in length which means that I can not use a radial because its leads do not spread that much unless they are long enough. So, if I solder the cut-off leads of the old cap to one or maybe both leads of the new, radial, cap, will the capacitance be affected significantly?


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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 5:45 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6617
Location: Montvale NJ, 07645
radioer wrote:
Thanks, I will try to measure it with two more meters but how does the multiplier works because if we multiply 20 by 0.1 for gold we get 2.0 Ohms.

Gold is the tolerance. Black is the multiplier.


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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 5:52 pm 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 1081
Location: Stone Mountain, GA
radioer wrote:
Thanks, I will try to measure it with two more meters but how does the multiplier works because if we multiply 20 by 0.1 for gold we get 2.0 Ohms.


Colors are Red, Red, Black, Gold. Black is multiplier (x 10^0), gold is tolerance (5%). So 22 x 1, 5%, 22 ohms.

As said, short the meter leads to see what the DMM reads and subtract that from the actual reading.

radioer wrote:
On a related issue, I have to replace two axial electrolytics ( which was the reason I got curious about the resistor), one is 470/10, the other 2000/18 but I can not find axials here so I have to go with radials. That poses a problem because the large cap goes sideways on the back of the board and measures an inch in length which means that I can not use a radial because its leads do not spread that much unless they are long enough. So, if I solder the cut-off leads of the old cap to one or maybe both leads of the new, radial, cap, will the capacitance be affected significantly?


No, lead capacitance only matters when you get down to picofarads.

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 Post subject: Re: Reisstor bands
PostPosted: May Tue 25, 2021 9:29 pm 
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Joined: Oct Sat 03, 2020 10:41 pm
Posts: 241
Quote:
Thanks, I will try to measure it with two more meters but how does the multiplier works because if we multiply 20 by 0.1 for gold we get 2.0 Ohms.

Note that your resistor has TWO red bands!! So it's not "Red, Black, Gold" it's "Red, Red, Black, Gold"

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 Post subject: Re: Reisstor bands
PostPosted: May Wed 26, 2021 12:43 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6617
Location: Montvale NJ, 07645
radioer wrote:
Hi Scott,
So you are in peaceful Montvale and most likely we crossed paths in some ham fest when I lived in NJ.

Not so peaceful anymore. They have built so many high density housing units in this area that many towns are more like cities now. The traffic is nuts and I can't wait to get out of here. Heading down to NC real soon.


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 Post subject: Re: Reisstor bands
PostPosted: May Wed 26, 2021 7:46 am 
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Joined: Feb Fri 27, 2015 3:19 pm
Posts: 141
Location: Athens, Greece
What a shame. I used to drive through that area on Sunday afternoons to enjoy nature and peace.
Good luck.


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