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previous: km hi Chris--i checked the amp today--... -- 1/22/2004 11:18 PM View Thread

Re: Marshall tones

1/22/2004 11:47 PM
M. Taylor
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Re: Marshall tones
You may have considered this already, but are you absolutely positive you wired the replacement OT correctly? I can certainly see how a mistake can happen with all the different lead color schemes out there. Since swapping the tranny was the event that made your JCM sound "ratty" and too quiet, I'd think you may be running a mismatched impedance ratio with your speakers. I know that EL34's with 430V on the plates and a 7400 ohm load using a Hammond OT certainly sounds the way you're describing...  
 
Also, right now I'd think you're biasing the tubes a little on the cold side:  
400V * 0.042mA = 16.8W or %48 of Pmax.  
(Pmax for a 6550 is 35W according to the RCA datasheet)  
 
While this is fine if you're liking the sound, since you're not so enamoured with it you might see how it is idleing anywhere as high as 61mA or 70% of Pmax. Keep an eye on the temperature rise of your transformers caused by the extra current, though if this amp used 6550s stock you'll probably be okay.

 
Replies:
km yes MT--the ot is wired correct.I ... -- 1/22/2004 11:58 PM
M. Taylor Oh wait! I forgot to consider your... -- 1/23/2004 12:10 AM