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Troubleshooting static/crackling noise on power up and power down only

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posbwp55@msn.com

(A)

I am using a CAT Ult MK2 pre and a CAT JL2 amp. Just today, one channel is crackling and popping on power up and down only. I suspect it is the amp. I pulled the input tube (on the amp)on the channel in question and checked it for noise on my VTV tube characterizer/tester. It is quiet. The system is dead quiet during play or idle. The noise is only there when turning the amp on (last component in chain to power up) and powering down the amp(first component in chain to power down). Any suggestion or trouble shooting ideas to isolate the problem are appreciated.
Bart

Follow Ups:

I've seen this problem - RFGumby 12:46:41 05/06/07 (2)
on various occasions, and in most situations it turns out to be a tube. On my personal gear,
it's either been input or driver tubes on
the amp, or often output tubes as well.
Take all the tubes from the left channel and swap them for the right.
Swap both driver and output tubes so it doesn't get too complicated to track down.
Remember to reset the bias's for the output tubes. If the problem follows the tubes,
then you at least know it's one or more of them from that channel. If not, it's an amp issue.
Best of luck,
RFG
- Re: I've seen this problem - posbwp55@msn.com 17:28:54 05/07/07 (0)
  RFGumby, THANK YOU! I can't tell you how relieved I am that it is a power tube and not the amp. I switched all tubes R to L and the noise moved to the left channel. I then reswitched the signal tubes.
  The noise remained in the left channel. I'll have to pull all the power tubes and check them on the maxi matcher. I've only had this set for a year and run them consevatively biased at about 30 ma when the recommended bias is 37 ma. They weren't very closely matched when new (16 tubes) so I may need to source them from a different vendor.
  Bart
- Re: I've seen this problem - posbwp55@msn.com 16:01:47 05/07/07 (0)
  Thanks for the advice guys. I'll try swapping all tubes from right and left channels. I hope it is a tube.
  Bart
Bad switch maybe? nt - risabet 21:59:20 05/05/07 (0)
nt

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