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No sound


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2/15/2003 5:20 PM
Bob DeRosa
No sound
I've got no sound with a new build - not even hum or hiss. It's basically a 50watt Plexi with an added gain stage.  
 
I'm thinking that it's the power section but I can't seem to track it down.  
 
Here are the vital signs:  
 
EL34 Power tube voltages:  
 
pin1 ~ 2mv  
pin2 - heaters are at 6.0vdc  
pin3 = 450v  
pin4 = 448v  
pin5 = -50v  
pin6 - not used  
pin7 - heaters are at 6.0vdc  
pin8 ~ 2mv  
 
I'm wondering about the hookup of my OEI PT. I'm only using the 8ohm tap so I taped off the 4ohm and 16ohm taps. I connected the green 8ohm wire to the tip connection of the output jack. I connected the orange wire to the sleeve connection of the output jack. The brown wire went to the fuse, the red and white wires went to pin3 of the el34 tubes.  
 
Anyone see anything obvious ?  
 
Thanks in advance
 
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2/16/2003 3:51 PM
scott
i dont see a problem with your connections, i would go over your ground connections. it sounds like something is open.
 
2/28/2003 2:16 AM
Don Symes

With no speaker plugged in, do you get continuity (a couple to several tens of ohms) from green to orange?  
 
You did have a speaker plugged in, right? (That's my special OMG it's broken! moment.)
 
2/28/2003 1:09 PM
Jani Koskelainen

Quick trobleshooting tip:  
(Maybe a bit hazardous though.. :))  
 
Take a plastic condensator rated abt. 1nF 2kV. Keep your finger in contact with another lead. With free lead touch grid of each output tube. If you hear mains hum, then output stage is propably OK. Then touch PI grids and if it hums, then everything from PI to speaker is propably OK. Next go one stage at a time towards input socket.  
 
BUT be careful. Capacitor blocks DC route to your finger, so you won't get shock if capacitor is OK. Don't touch anything else in your amp while doing that anyway! And touch ONLY grids just in case..  
 
I've used that trick several times for quick troubleshooting.  
 
-Jani-
 

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