Tweakers' Asylum

RE: soft recovery bridge rectifiers need bigger heatsinks ?

202.14.247.4

kalido

In Reply to: RE: soft recovery bridge rectifiers need bigger heatsinks ? posted by wheezer on March 17, 2009 at 00:05:41

hi wheezer , its strange that schottkys worked fine but not the DYNs. I guess as Al pointed out, it could be due to the higher forward voltage ? It'says 2.5V max as compared to 1.1V of the stock. To my knowledge, there aren't any surge circuits in the amp just before the transformer. It just the turn on/off switch and a cap across it. And that goes all the way into the transformer. Also wheezer, could u suggest a method to test those output BJTs pls ? i did test for voltage across the 8 emitter resistors and they seem to be fine. Is this adequate to test the BJTS?

Edits: 03/17/09

Follow Ups:

RE: soft recovery bridge rectifiers need bigger heatsinks ? - wheezer 16:36:55 03/17/09 (2)
Check the cap on the switch.
Your DMM probably has a test for diodes?
If the emitter resistor went, things would be a whole lot worse.
Test the BJT's and signal diodes just after the rectifiers and then the output BJT's.
Does the Rotel have Pre. out's?
- RE: soft recovery bridge rectifiers need bigger heatsinks ? - kalido 20:16:39 03/17/09 (1)
  the cap on the wsitch looks like a big ceramic type. Strangely the value is was not stated in the shcematics.
  
  The DMM does have diode test but how do i test the BJTs with it ? Unsolder them and test one at a time u mean ? Wouldnt it not work at all if any of the pre-driver or output BJT gone bad ?
  
  By da way , it does have a preout.
  - RE: soft recovery bridge rectifiers need bigger heatsinks ? - wheezer 20:23:54 03/17/09 (0)
    Try in the circuit first. I've found more than not, in circuit will work.
    When those little three legged cockroaches go, "typically" you'll get nasties.... hummmmmm or distortion.
    But, have a looksee for suspicious looking caps and resistors, burnt, fried or blown.
    - Testing BJT's (Open in New Window)

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