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RE: What would cause filament to burn out on My 300B tubes

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JayD

In Reply to: RE: What would cause filament to burn out on My 300B tubes posted by 6bq5 on July 14, 2022 at 17:33:15

Thanks. I thought initially that it might just be a bad tube, but having it happen twice in the same amp (right channel) seems unlikely.
What might cause a change in the filament supply?
thanks again.

Follow Ups:

RE: What would cause filament to burn out on My 300B tubes - Paul Joppa 21:01:22 07/14/22 (3)
That depends on what the filament supply looks like - i.e. we need to see a circuit diagram.
- RE: What would cause filament to burn out on My 300B tubes - JayD 14:27:50 07/15/22 (2)
  Don't have the circuit diagram handy but it is a Welborne DRD (direct reactance drive) based on Jack Elliano schematic.
  - RE: What would cause filament to burn out on My 300B tubes - Paul Joppa 17:18:33 07/15/22 (1)
    Google turned up the kit manual, which shows a 6.3v winding into a rectifier bridge and CLC filter. Hard to see any way for that to produce more than a normal voltage unless maybe the filament choke is shorted. If your power line voltage is high, you might see a small increase in voltage.
    
    It's probably worthwhile to measure the filament voltage on both monoblocs.
    - RE: What would cause filament to burn out on My 300B tubes - JayD 10:25:11 07/17/22 (0)
      Thanks for the input

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