Tubes Asylum

RE: Runaway 7581A

63.247.31.12

In Reply to: RE: Runaway 7581A posted by Thermionic27609 on July 02, 2009 at 20:12:22

Do both 7581A start going ballistic, together? Or just one tube? You may want to check the BIAS POWER supply for consistent negative voltage in the range in the schemo.
Also, 7581A usually biased hotter and put out more watts than 6L6GC. Maybe the extra current/voltage needed is revealing a parasitic problem, that the stock 6L6GC wouldn't reveal? A WAG.

Edits: 07/03/09

Follow Ups:

RE: Runaway 7581A - Thermionic27609 05:28:40 07/03/09 (6)
- RE: Runaway 7581A - FenderLover 05:38:01 07/03/09 (5)
  - RE: Runaway 7581A - Thermionic27609 08:06:07 07/03/09 (4)
    - I usually change those resistors - FenderLover 16:05:24 07/03/09 (3)
      - pink ceramic based STR-415 (Sylvania specials) - FenderLover 04:21:20 07/04/09 (2)
        
        RE: pink ceramic based STR-415 (Sylvania specials) - Thermionic27609 07:16:40 07/07/09 (1)
        
        Plate voltages - FenderLover 04:52:28 07/10/09 (0)

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