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Mesa 400...6550/KT88?

#81
Sorry you were talking about the 400 non plus. The 400, d-180, m-190 all have about 540 volts b+ so they are a bit harder on tubes but my recommendations still work well in those amps.
If you're worried about them holding up you can use 6550, or KT88's in it with the proper bias adjustment.
 
#82
agedhorse said:
Whoa, the heater current reqt. for the 12BH7 is TWICE that of the 12AX/AU/AT type tubes. This is NOT a recommended substitute.

Note that the output stage is NOT cathode biased, I don't follow your logic or reasoning.

Modifying products is taken at your own risk, and the results could result in either a very costly repair, or possible an unrepairable amp. Especially important when considering the thoughts you have posted.
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Thanks I really appricieate and will follow your advice. I did ask the tech at Mesa and he was very vague about it. No damage so far. I'm a lucky guy. Thanks again that was nice of you to steer me away from trouble.
Good karma to you sir.
 
#83
Bazz1111 said:
Thanks I really appricieate and will follow your advice. I did ask the tech at Mesa and he was very vague about it. No damage so far. I'm a lucky guy. Thanks again that was nice of you to steer me away from trouble.
Good karma to you sir.
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I asked the tech about the 6550s and the 12au7s and he said " I use 5881 STRS and 12ax7s in mine but you can use any compatible tube you want. Maybe they were trying to drum up some service work.
I know the 12au7s are compatible. But probably not the 6550. I have the 400+.
 
#84
Bazz1111 said:
Thanks I really appricieate and will follow your advice. I did ask the tech at Mesa and he was very vague about it. No damage so far. I'm a lucky guy. Thanks again that was nice of you to steer me away from trouble.
Good karma to you sir.
Click to expand...
Nobody likes to repair damaged amps ;)
 
#85
Bazz1111 said:
I asked the tech about the 6550s and the 12au7s and he said " I use 5881 STRS and 12ax7s in mine but you can use any compatible tube you want. Maybe they were trying to drum up some service work.
I know the 12au7s are compatible. But probably not the 6550. I have the 400+.
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The 6550 has a higher heater current draw, I would not consider it compatible. I do not know the specifics of the design history of the amp, so I would hesitate to recommend anything that might endanger your amp. You could ask one of the techs (Mike B. is probably the most familiar with these) specifically about using the 6550 in your amp, be sure to have the serial number because he may need to go back and look at the revision history.
 

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