Tweakers' Asylum

Preamp Corrupting tubes

24.107.58.134

sept79

Have a preamp with two 6N1P tubes and a 6X4 tube rectifier. The left channel 6N1P tube seems to last for approximately 12 hours before it starts to either get noisy or starts to have high frequency distortion. Any simple things I might start looking into before I take it to a local repair shop? Does this happen often? Help!

Thanks for any advice.

Follow Ups:

RE: Preamp Corrupting tubes - reb 09:04:45 11/22/07 (0)
Could be the filament voltage on the left channel is well above 6.3volts, causing permanent damage to the tube. Measure the filament voltage ..........
Exchange tube across L & R channel, & hear. (nt) - cheap-Jack 11:36:51 11/19/07 (5)
.
- RE: Exchange tube across L & R channel, & hear. (nt) - sept79 13:09:49 11/19/07 (4)
  If I move the corrupted left channel tube to the right channel socket, the right channel now displays distortion.
  - So the left channel tube is defective, replace it. (nt) - cheap-Jack 13:22:09 11/19/07 (3)
    .
    - RE: So the left channel tube is defective, replace it. (nt) - sept79 14:14:39 11/19/07 (2)
      How many times do I replace this tube in a three month period before I am to suspect that there is a problem other than a bad tube? As I indicated in the original post, I can't make it through a week before I have a corrupted left channel 6N1P tube. I probably am hearing distortion out of the left channel after 3 or 4 days.
      - If this has been a repeating fault,.. - cheap-Jack 12:50:51 11/20/07 (0)
        
        In Reply to: RE: So the left channel tube is defective, replace it. (nt) posted by sept79 on November 19, 2007 at 14:14:39
        
        Hi.
        
        Could it be due to leaking I/P coupling or O/P coupling caps of the left tube amp stage?
        
        c-J
      - Check tubes' operating points. - sser2 19:03:08 11/19/07 (0)
        
        In Reply to: RE: So the left channel tube is defective, replace it. (nt) posted by sept79 on November 19, 2007 at 14:14:39
        
        Measure DC voltages on plates and cathodes of L and R tubes. Calculate current and dissipated power. Power higher than 2 W per section may cause premature tube failure. The reason of out-of-spec operating point could be leaky coupling capacitor or shorted resistors connected to the section.

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