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1st amp power amp problems...

8/27/2000 2:30 AM
Spencer1st amp power amp problems...
Hi everyone, just finished my first scratch build and there seems to be a few problems with the power amp that I just can't seem to figure out. First off, it's a 60-watt 2x6L6 (Tesla) in class AB1 PP with a pentode / triode switch, the speaker outputs are isolated from the chassis.  
 
-Problem 1: in triode mode, the amp isn't noisy at all, when in pentode mode, it squeals (but you can still hear the guitar signal come trough). What could this be? Is it related to my next problem?  
 
-Problem 2: The output jacks are isolated from the chassis (and any ground). When I ground the common (black) wire to it's respective star point, the amp squeals uncontrollably at what seems to be full volume. Doesn't this commone wire need to be grounded for proper operation?  
 
-Problem 3: The amp has prescence and resonance controls connected to the 4ohm tap on the OPT (a hammond 1650N), however they seem to have very very little (if any) effect, is this related to the OPT common wire not being grounded?  
 
If anyone could even scratch the surface on these issues, I'd really appreciate it as I'm really dissapointed that after 6 months of building + designing the thing I still can't use it! Doh!  
 
Thanks in advance everyone! ...Spencer

 
Replies:
Tracy Hi SpencerI think w... -- 8/27/2000 3:20 AM
Les Problem 1: is probably related to p... -- 8/27/2000 3:33 AM
Spencer Thanks guys, the switching of the p... -- 8/28/2000 5:50 AM