Diode replacement problem

Discussion in 'General Electronics Chat' started by junlokk, Jul 6, 2014.

  1. junlokk

    Thread Starter New Member

    Jul 6, 2014
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    Hello, my name is jun,
    I am looking for a replacement of my silicons diodes (10D10) in a old amplifier. I looked all over the internet for 4 months now, i am desesperate you are probably my last hope !

    First I found the specifications here :
    http://pdf1.alldatasheet.com/datasheet-pdf/view/114655/IRF/10D10.html

    What is the closest equivalent (direct replacement), on datasheet archive I found these references :
    - 1n5399
    - 1n4007
    - nte 125
    - byw56

    But all of these are a little bit different, and i don't know diodes enough to fully understand the use of all those values.

    can you help me ?
    Thank you.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,013
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    Silicon rectifier diodes are generally non-critical when used as line frequency rectifiers. Any diode that has an equal or greater maximum current and reverse voltage rating should be fine.
     
  3. junlokk

    Thread Starter New Member

    Jul 6, 2014
    11
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    thank you very much,
    so as long as the diode is similarely spec'ed it will not change the sound of my amplifier ?

    I should only look at ? :
    VRRM = 1000V (Maximum repetitive peak reverse voltage)
    FI(AV) = 1.5A (Maximum average forward rectified current)

    I was looking at JUNCTION CAPACITANCE (Cj) and REVERSE CURENT (IR), but 'forward voltage drop' (VF) was the one giving me headache as it is variable with the temperature..........:mad:

    Do you know what is the purpose of all these in a bridge rectifier configuration ? Useless ?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    It would appear that they are rectifying the AC voltage from the power transformer to generate DC for the amplifiers. A bridge rectifier configuration is common for this to provide full-wave rectification if the transformer output is not center-tapped. Reverse current, forward voltage drop (which varies with temperature for all types of solid-state diodes) and junction capacitance are normally not an issue for such applications.
     
  5. junlokk

    Thread Starter New Member

    Jul 6, 2014
    11
    0
    Thank you again you are really helping me after months of problems :)
    Yes they're connected to the PT to generate DC, which goes directly to the tubes heater. So this amplifier is particularly sensitive to plate voltage. That's why I wanted to get the closest possible diodes.

    Problably my last questions :
    1) do you know if the recovery time (Trr) is critical in this application ? (I forgot to ask before sorry)

    2) about the Maximum instantaneous forward voltage (VF), i found this thread but i did not understand completly, how it apply to bridge rectifier (i will continue to read it)
    http://forum.allaboutcircuits.com/showthread.php?t=6314

    Thank you again for taking the time to respond.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,013
    3,233
    1) Diode Recovery time is not an issue for diodes operating at the normal main's frequencies (50/60Hz). Actually, fast recovery-time diodes can generate more switching noise due to their more abrupt turn-off when the diode voltage is reversed once each cycle (which generates more noise harmonics).

    2) All silicon junction diodes of the same current rating tend to have nearly the same forward drop however it's defined. Capacitor filtered bridge rectifiers have a large peak current since the diodes only conduct near the peak of the sin-wave so the peak current can be much larger than the average DC output current, so the instantaneous peak voltage may be of some interest (but I don't think it's a factor in buying the diodes for your amp).
     
  7. junlokk

    Thread Starter New Member

    Jul 6, 2014
    11
    0
    You are the best thank you very much
    I do not have word to say how you cleared everything for me.

    So ultra fast diodes can introduce more switching noise to due to the more abrupt cuttoff (deeper slope) it makes sense.

    I have heard a lot about switching noise, and someone even said to me that I should use ultra fast diodes to reduce switching noise, because during the switching delay, standard diodes produces all kind of frequencies until the radio frequency range (from where it can be heard?) and this noise can be fed into the tube plates (after riding through the DC voltage rail). FALSE ? or this guy was misinformed ?

    You helped me a lot. i am grateful so thank you ;)
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,013
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    I think that's not true. The faster the cutoff (faster risetime) the more energy is in the harmonics. The harmonics in the audio range can be heard directly if they get into the amplifier. Higher frequency harmonics can be sometimes rectified by circuit non-linearities to also be heard. These harmonics produce a buzz at twice the line frequency (for a full-wave rectifier). Sometimes small value capacitors are placed across each diode to suppress these harmonics, if they are a problem.
     
  9. junlokk

    Thread Starter New Member

    Jul 6, 2014
    11
    0
    Thank you very much, I will resume tell me if I got something wrong please.

    So for 50/60hz power supply no need for ultra fast diodes, you will not get any benefits, plus due to the faster cutoff it will introduce more noise than standard diodes (a buzz : since it's in low frequencies, at twice the 50hz=at 100hz). This buzz can be suppressed by using capacitors across each diodes. Also it can be "lowered" by non linearity in the circuit (the higher the inductance the less noise, i guess ?)

    So what do you think I should use ?:
    -Standard diodes alone
    -Strandard diodes + caps (I think this is the solution ?)
    -Ultra fast diodes + caps

    By the way do you have a business or something ? Since you helped me I will talk about it to my friend, to help you.
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,013
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    Inductance, per se, is not a "non-linearity", but it can be used to help filter out noise.

    I would go with standard diodes and only add the caps if you have a noise problem.

    Nope, no business, just a retired analog engineer who likes design. ;)
     
  11. junlokk

    Thread Starter New Member

    Jul 6, 2014
    11
    0
    Thanks again :)
    I mistaken chokes as being non-linear with inductance, by non-linearity you mean non fixed differences between input-output.

    I will start choosing something from these cross references, and get to work.
    Now i am confident it will not completely change the amp :p

    I will continue first my work on my noisy "custom circuit" tube amplifier.
    Can I get back to you in MP if i have a problem with this amp ?
     
  12. crutschow

    Expert

    Mar 14, 2008
    13,013
    3,233
    Non-linear is generally where the output of a component/system is not linear function of the input (e.g. a diode).

    Good luck with your fix. :)

    Post if you have any problems.
     
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