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In Reply to: RE: Test my 300B tubes? posted by Chip647 on February 07, 2025 at 12:39:10

My 300B se amp was losing sound out of 1 channel after a couple hours of play.
It would always come back on fine after a shut down and turn back on. But persisted to happen.
Checked and swapped the most of the obvious causes/solutions, but it turned out to be a cracked solder joint. Which I got repaired. Same problem happened after the repair. I have 3 pairs of fairly well used 300B tubes, and wondering if several of these are just at the end of life. In my 30 years of enjoying tube amps, I have only had an EL34, which was noticeably distorting and a 6C33C-B that went thermal red.
Anyway just thought I'd check the tubes before taking it back in for another check up.

https://phys.org/news/2017-08-astrophysicists-moons-saturn-m (Open in New Window)

Follow Ups:

If only one channel, just swap tubes from left to right. - Chip647 14:49:10 02/08/25 (1)
If the sound problem follows you know what the issue is.

However, given you have the issue after the amp heats up, it is likely another cold solder joint or a failing resistor/cap. Tubes themselves usually do not display this type of failure as the tube reaches full heat in a matter of minutes.

What amp is it?
- Music everywhere - theromium 07:37:53 02/10/25 (0)
  Elekit TU-8600S, which I'm really enjoying, almost as much as the 45 se amp.
  - https://phys.org/news/2017-08-astrophysicists-moons-saturn-m (Open in New Window)

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