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hot tubes, I mean really hot

8/10/2005 1:57 PM
pete
hot tubes, I mean really hot
Hi all,  
 
So I just finished putting together an 800 clone as found in TUT 3, but I get the following problem. My power el34s get way too hot. Red hot. I checked all of my connections, and everything seems right. Using the dissipation bias method, I turn my pots as to create the most negative voltae possible on the control grid. All volumes and eq turned all the way down and no input.  
 
So I plug in an output tube, and turn on the amp. At first it warms up ok, heaters orange, everything good. After a few seconds, the plate starts to glow orange and the glow starts to spread across the plate. The smoke comming from the plastic base of the tube tells me no good. All of this happens within about 30 seconds, then I turn the power off. Also, as the tube starts to overheat, there is a progressivley louder, yet dull, hum from my speaker.  
 
When I have no power tubes, everything checks out ok. Preamp tubes light up fine, no sounds from the speaker. The voltage on the control grid reads about -5.6 to -5.4 Volts.  
 
I have tried using a different output tube, but still the same problem. I have tried all four tubes in at the same time, but still same problem. This circuit is supposed to allow any number of tubes to work correctly, so having one tube in at a time isnt the problem. If anyone is familiar with this sort of problem I would greatly appreciate any help. Thanks!  
 
Rock n Roll.  
 
-Pete

 
Replies:
pete Oh I forgot to mention, I cannot ev... -- 8/10/2005 2:00 PM
Mark Black Yikes! You should be seeing someth... -- 8/10/2005 3:33 PM
Enzo Only 5 volts of bias? My God, thos... -- 8/10/2005 7:57 PM
pete Hi everyone,Ok so t... -- 8/12/2005 9:44 PM