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RE: Check the power tubes next

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In Reply to: RE: Check the power tubes next posted by Ralph on April 17, 2012 at 12:07:59

It is a tube problem. I smoked couple of power tubes before being cautious enough with known good tubes from the other mono block and sound output has been restored. Both tube failures occurred to right rear left bank socket resulting in an immediate severe flash upon turning on full power. Violence of the flash seemed more then just an arc over. I have this bad habit of not discarding suspect 6as7 tubes that I have culled out over time for noise, bias and offset adjustment problems. i eventually start to reuse these as time goes on thinking there might be a good one or two in the bunch. I checked out your visual tube inspection link and might now have better luck culling tubes in the future. Time for some new ones!

Aside from this apparent tube issue, the capacitor that appears to be slightly swollen and leaking or corroded? I presume this is a source of sound quality degradation and will only get worse. Could this be causing a minor persistent hum? Would Atma-sphere have the correct replacement 1600uf power supply capacitor which I could purchase. Is it possible a bad 6sn7 could cause power tube instability and or failure? I do not have a tube tester so resort to trial and error when issues arise.
Dennis

Follow Ups:

tube failure - Ralph 09:12:07 04/18/12 (4)
The 6AS7Gs just seem to arc on their own. So far we have yet to encounter a problem in an amplifier that causes the tubes to arc.

Stay away from 6AS7As and GAs. They don't seem to hold up well.

If you have a cap bulging, it is indeed time for replacement. But I would consider changing the lot of them rather than just the one. We've not used that value in a while- so I am thinking that this amp is about 15 years old. If one cap is already failing, the rest can't be too far behind. If one cap is bad in the output section and the rest are 'ok', it would cause the amp to hum. These days the value we use is 2200uf rather than 1600uf. If nothing else it will sound better with the increased value.

There are a lot of updates available too! If you have us update the amp to the latest level, the warranty reactivates.
- RE: tube failure - roscoeiii 12:28:33 04/18/12 (3)
  And Ralph, you have mentioned in the past that you recommend keeping the amp in warm-up phase for 72 hours after inserting new 6AS7s to prolong thier life. Any risk of damage if they arc during that warm-up/break-in phase? (since likely folks will be working & sleeping at some point in that 72 hours).
  - The tubes can't arc during pre-conditiong as there is no B+ nt - Ralph 10:00:59 04/19/12 (1)
    -
    - RE: The tubes can't arc during pre-conditiong as there is no B+ nt - roscoeiii 10:21:55 04/19/12 (0)
      Thanks as always Ralph.
  - RE: tube failure - djm1969 16:57:41 04/18/12 (0)
    Thanks Ralph and all you others for the help! I think I will be OK from here. This was my first experience with the Asylums forum. What a great bunch!
    Regards
    Dennis
RE: Check the power tubes next - tyu 05:32:38 04/18/12 (0)
Could this be causing a minor persistent hum....YES...An there are some small upgreades to the output tube cathoides...like add the 5ohm 5watt res. if you dont have...this well give you diff.... sound call Ralph.....you can get capes anywere...goodluck

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