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Carbon comp resistors

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by 900, Jun 24, 2006.

  1. 900

    900 Member

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    Can Carbon Comp resistors produce a slight crackling and popping noise while they warm up? It's always only in the beginning if I switch from standby to ON rather quickly (30 - 60 sec). If I let the amp warm up on standby for 2 - 3 minutes it doesn't happen. Otherwise the amp has no issues. Tubes have been replaced lately.
     
  2. Rich M

    Rich M Member

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    Do you store the amp someplace humid?
     
  3. Frostbite Slim

    Frostbite Slim Member

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    It COULD be the plate resistors, or maybe perhaps the OT has some moisture in the core. How does the amp sound otherwise?

    BTW- I would let the amp "warm-up" a minimum of 5-10 min. If you don't let the powetubes warm up properly you get what is called "Cathode Stripping". NOT GOOD for powertubes!
     
  4. Tuberattler

    Tuberattler Member

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    10 minutes is a bit excessive, most power tubes will be warmed up enough in 2-3 minutes to be ready to go.

    I had a cold solder joint on a Filter cap for the board do what you're describing..only when it was cold. Warmed up no prob,,then it started to get worse after a few month..so trouble shoot & resolder!

    Good luck, which amp are we talking about??
     
  5. twangbanger

    twangbanger Supporting Member

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    did this start after you replaced the tubes? I only ask because I had a el84 going bad that did that when the tube was warming up and went away after that! but it just got worse till I replaced the tubes.
     
  6. Texasamp

    Texasamp Member

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    As Frostbite Slim said, plate load resistors get the brunt of the surge of dc when standby is switched to the "On" position. CC resistors over age, or over to much heat from being soldered on so much causes them to be brittle and to drift upwards in resistance.

    I use all Allen Bradley cc resistors in my builds and have gotten that pop crackle on a new amp. Cold solder joints at the plate load resistors can be the culprit as well. I normally will suck the solder out then resolder them back. If that does not fix the problem I then replace the 100k, 82k's (Fender Amps).

    Sometimes chasing those little pops can be a real pain though as you may spend many hours tracing it down and also replacing many components that were good in the first place.

    Good Luck,
    Darrell S.
    Texas Amplification
     
  7. 900

    900 Member

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    Thank you for the replies. The amp is not stored humid. It had similar symptoms before they replaced the tubes, but only 10x worse/louder - with occasional volume drops etc - and they wouldn't go away when the amp had warmed up. According to the tech, that problem was based on the power tubes. After the tubes have been changed an the amp re-biased it was fine, with full power again and 100% noise-free for about 1 month after which the slight poppin an cracklin started (maybe I just let it warm up long enough during the first month). It's not getting worse and otherwise the amp sounds normal.

    Anyway, from your replies I understand there can be different reasons for the symptoms and since I'm not a tech I'll take it to the local amp-guy for a further check..........
     
  8. tmac

    tmac Goldmember Gold Supporting Member

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    I know for a fact that some preamp tubes will pop and crackle when the amp is standy switch is turned on and this is normal. In my experience the newer Sovtek tubes like the 12AX7WA's are prone to this. JJ's don't seem to do this or any of my NOS tubes.

    Try your old preamp tubes and see if it still does it.
     
  9. donnyjaguar

    donnyjaguar Member

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    I wouldn't rule out dirty tube sockets either.
     
  10. lastwinj

    lastwinj Member

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    this happens when you turn the amp on with the standby off, and the full b+ rails hits a cold tube.

    waiting 10 minutes for ti to get warm is a waste of time. 45 seconds to 1 minute max.

    germ
     
  11. TheAmpNerd

    TheAmpNerd Member

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    This is typically not a problem in amps with B+ less then 500V.
     
  12. 900

    900 Member

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    I'll take the amp to a tech next week. I'll post what it has been when I'll get it back.
     
  13. trdlasvegas

    trdlasvegas Member

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    I certainly love more busisness, but excuse me for being a wise as*, Why bother?

    You did say it's totally quiet after a couple of minutes, and there were no other problems. I say just play it and make some music with it.

    -Tony
     
  14. brad347

    brad347 Member

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    maybe the tube sockets are dirty, maybe the sockets need to be re-tensioned (common if you went from russian tubes to NOS), or maybe the tag board itself is intermittently conductive until it heats up!

    All possibilities.
     
  15. 900

    900 Member

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    [SIZE=-1]You hit the nail on the head. I was because of a two Sovtek-made 12AX7 "Groove Tubes". They have been replaced with JJ's and now the amp is whisper quiet. :AOK
    [/SIZE]
     

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