2. amps-preamps
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Bad Tube? Which one?

Sorry to have to ask this question. I have been running a Rogue Cronus Magnum for two years. I've never tube rolled and still using all the original tubes. Tonight it's sounding muddy and distorted, even at lower levels. I stopped the CDP and checked the bias on the KT90's and they're all a perfect 35 mA. Does this mean that the KT90's are not the problem tubes and it's one of the 12ax7's or 12au7's?
donjr
tom6897's avatar
tom6897
1,484 posts
 
Always a good idea to keep some spares on hand for these types of investigations.
rrog
1,958 posts
 
Tom6897 is right. When you own tube equipment you should always have a spare set of tubes on hand.
onemug
784 posts
 
I'll 3rd what Tom6897 and Rrog said.

A spare set will come in handy when:

1. Things go bump in the night. I just had a tube rectifier develop a short. Replaced the fuse and rectifier and was good to go.

2. Diagnosing. My 2a3 amp was sounding a little flat. Tubes measured ok and I could bias them properly. Put in a new set of 2a3's and all the life came back.

Even though your KT90's bias "a perfect 35 mA" they may be tired although gambling, I would bet on one or all of the 12's. Get a new set of them first, they're cheaper.
donjr OP
1,335 posts
 
I do have a spare matched quad of KT90's. I'll call Mark at Rogue and also get some spare 12's.
donjr OP
1,335 posts
 
So I guess I should have mentioned that my CDP is also a preamp. The issue was the volume on the CDP was turned up all the way and was clipping the input to my amp. I can't take credit for figuring this out. It was my amazing local salon owner that made me aware of this as being a possibility. I'm still ordering spare tubes because the pain of one week without music was worse than passing a kidney stone (been there). Thanks for all the input.
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