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Old Resistors

Discussion in 'General Electronics Discussion' started by David Adonias, Jan 9, 2018.

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  1. David Adonias

    David Adonias

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    Jan 9, 2018
    Hi everyone! I'm replacing some old resistors in my audio equipment and noticed that there is no spacing between the 3rd and 4th band of the resistor to tell which side to read.... ex: I have large red band, a purple, a gold, and a silver band... so would the first band be red or would it be silver???? if the first band was red the my resistor would be a 90kohm resister with +-0.05% tolerance but if the first band was silver it would be 120mohm with +-2% tolerance which is a big difference!!!!! let me know thanks!!!!!!
     

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  2. 73's de Edd

    73's de Edd

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    Sir David Adonias . . .

    REFERENCING TO:

    https://www.allaboutcircuits.com/textbook/reference/chpt-2/resistor-color-codes/

    You have yourself their specified category 2 code, so enjoy all of that 2.7 ohms.
    Looks to be about 1 watt . . . considering no side referencing to a coin or actual measurement.
    Should you have found it having RED-VIOLET-SILVER-GOLD, you would have a 0. 27 ohm resistor.

    73's de Edd
     
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  3. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    It's a 2.7Ω, 10% tolerance resistor. See this chart for four-band and five-band resistor color codes..
     
  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    WTF did you get this "information"? It is totally wrong!
     
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    You do not know the color code so here it is. The resistors are red=2, violet=7, gold= 0.1 times and silver= 10%. So they are 2.7 ohms, 10%. Are you going to guess their power rating?
     

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  6. Audioguru

    Audioguru

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    Sep 24, 2016
    Hevans beat me because I was changing the batteries on a Sudoku thingy.
     
  7. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I agree it's 2.7Ω 10%, but it raises a good question. What determines the first band from the last? In this case its obvious that silver is the tolerance band because it can't be a selection for the first band.

    Is it the fact that the first band is closest to the left hand side, or because the band is wider than the rest?
     
  8. David Adonias

    David Adonias

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    Jan 9, 2018
    Thanks everyone I'm new to this but have a knack for learning very quickly.... I really appreciate all of the advise and help!!!!!! I was reading yellow and gray instead of gold and silver duhhhh..... Thanks again!!!!!
     
  9. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    I often have trouble figuring this out, especially when there are five or more colored bands. If the resistor is still intact and not crispy-fried, my trusty multimeter will usually get me into the ballpark range of the resistor value, from which I can then usually figure out which way the color code should be deciphered. Best way is to find the original schematic in which the resistor is identified and read the value from there. Even that isn't bullet-proof as sometimes the manufacturer will change the part without updating the schematic. Be sure to check for errata sheets associated with older, vintage, electronics equipment.
     
  10. David Adonias

    David Adonias

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    Jan 9, 2018
    So i guess I would use OHMS law to find the current of the resistor so I=V/R so 120v / 2.7ohms = 44.44 but that doesn't seem like the wattage of this resistor.... how would i find the exact wattage of this resistor in order to replace it? This is the amp it came from.... Thanks
     

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  11. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Usually the LAST band is silver, gold red or brown (10%, 5%, 2% and 1% respectively - tolerance) but a multimeter is sometimes the easiest way to get it right.

    Wattage is a 'physical' thing and best determined by length/width and comparison to similar resistors. Most suppliers will have dimensional drawings of them.
     
  12. BobK

    BobK

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    Jan 5, 2010
    What makes you think there is 120V across the resistor? (Hint, there was not or you would be looking at the ashes of a resistor.)

    And even then, your calculation produced the current through the resistor, not the power. The equation for power is:

    P = V^2 / R

    Which comes to 5333 Watts, which is why the resistor would not have survived.

    Bob
     
  13. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Yes, Me too but i was wondering if there was a helpful clue like the 1st stripe being closer to the left. I guess not.
    Although sometimes I've noticed a slight space between the last two bands that makes it evedent.
     
  14. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Red or brown would have me scratching my head without my trusty meter.
     
  15. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir David Adonias . . . .

    Got electricity back yet ? in order to run / repair that thing.
    AND do you DO fully recognize, that you have got yourself a early 70'ish Wurlitzer organ amplifier ?

    Also near the right ORANGE drop capacitor . . . . don't you have a whole scheiss-pot full of components that
    have been pulled from that immediate area of the PC board ?

    Looks like one 2.7 Ω resistor got totally overloaded and the other, you just clipped its leads out of circuit.

    You should find one or more shorted power output transistors on the heat sink.

    73's de Edd
     
    Last edited by a moderator: Jan 11, 2018
  16. David Adonias

    David Adonias

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    Jan 9, 2018
    Hey Edd, yes we finally got power back on the Island after a long struggle (at least where I'm working) and yes it is a 1973 wurlitzer 4373 organ with the orbit 3....... I was modified some things on it when it burned out and also the buss GJV2 250 v fuse blew right next to it...... but before that I had it working great and wanted to modify the amp for an early hammond tube amp to drive the speakers..... I managed to unsoder the resister and the clipped the fuse out but cleaned circuit since.... yes when I got the organ it looked like someone did some crazy Frankenstein madness to it so there are probably things missing out of the cards but i cant find the schematics for this organ..... I want to do some real freaky things to it but need to fix this issue first.... since the resistor blew on the output card your def right about the transistors this usually happens with vintage gear and just getting to know a little more!!!!! thanks for the advice and love for vintage gear!!!!!!! What transistors would u suggest??? thanks!!!!
     
  17. hevans1944

    hevans1944 Hop - AC8NS

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    Ha! Whut a find! And is that a 115 VAC convenience outlet on the right side for connection of an add-on Leslie Speaker?

    [​IMG]
     
  18. Audioguru

    Audioguru

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    Sep 24, 2016
    I never saw a Leslie speaker or looked it up. Did it rotate to make a wah, wah sound?
     
  19. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    It did not make the "wah, wah" sound you hear when the player alternately mutes and un-mutes a brass instrument such as a trumpet. The Leslie sound is quite unique, but can probably be reproduced today fairly easily with a Digital Signal Processing (DSP) chip.

    The Leslie system was an "add on" to an existing electronic organ. It generally had two loudspeakers with a 800 Hz cross-over frequency. The low-end range audio loudspeaker (woofer) did not rotate. Instead it faced (usually downward) a baffle that rotated at a variable rate of speed from slower (chorale effect) to faster (tremolo effect),

    Read the Wikipedia article and play the "sound bite" near the beginning of the article to hear what the Leslie effect sounds like. It is unique among musical instruments in that it both amplitude modulates and frequency modulates (through the Doppler effect) the sound emitted from the speakers. There is a low audio range speaker (woofer) that is usually pointed downward toward a rotating. variable-speed, motor-driven baffle. There is also usually a high audio range horn-speaker (tweeter) that also rotates, but I have no details on how that was implemented.

    In the Conn electronic theaterette organ that I once owned, the Leslie low-end woofer speaker was mounted horizontal (probably to save space) in front of the rotating baffle. The effect was not as pronounced as the one heard on the Wikipedia sound bite. There was no Leslie high-end tweeter in my organ.

    upload_2018-1-9_23-21-38.jpeg

    Electronic organs are a lot of fun to "play" with, both musically as well as electronically, but I must have a "tin ear" because (1) I never learned to read or play from sheet music, and (2) was never, ever, asked to play the organ.
     
  20. David Adonias

    David Adonias

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    Jan 9, 2018
    Yes hevans1944 there is the outlet for the leslie speaker and actually this organ had an addition to it which was the leslie connector unit pictured below..... but this organ had something else with it that is even more crazy...... The original Spectra tone tremelo speaker(also pictured below) that created a unique sound experience unlike no other.... it wasn't working at the time but it works now as a separate unit that I managed to insert a 1/4in plug so guitars ect can experience the specta tone...... I have began building more of these speakers based on this design already!!!! truly unique.... but i cant wait to show u what i will do to the orbit 3 when it is done...... Frankenstein creation all analog!!! Super happy U get my madness!!!!!!
     

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