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What Did I Do Wrong?

I have a Rogue Cronus Magnum integrated with the KT120 tubes. I wanted to try the EL34 sound in my system so I purchased 4 Shuguang EL34B tubes which were graded and matched from Upscale Audio. I checked with Rogue and was told to set the bias at 30ma. I received the tubes today, installed them and let them warm up for 30 minutes. The sound was a little ragged and distorted and try as I may, I couldn't get a reading on the bias meter.

Thinking I wrecked the amp, I reinstalled the KT120 tubes (thank God I marked which socket they came out of) fired the amp up and the sound is again full with no distortion. I checked the bias on the KT120's after 30 minutes and the bias on one tube was off a little.

Why did the EL34 tubes sound distorted and why couldn't I bias them? What did I do wrong? Do you think these tubes are all toast now?
128x128stereo5
analogluvr
800 posts
 
So u got a reading fine with the 120s?
dweller's avatar
dweller
2,152 posts
 
Another thought:
Does the Rogue have a pentode/triode switch?
It may be set to the wrong one for EL34s.

Also, Have you tried to bias from a cold start?
It says you biased after letting the tubes warm up for half-an-hour.
I used to bias my Almarro 318 at turn-on then check after 30 minutes (of playing music).
stereo5's avatar
stereo5 OP
2,766 posts
 
09-05-15: Analogluvr
So u got a reading fine with the 120s?

Yup, everything is fine with the KT120 tubes back in.
reynolds853
367 posts
 
From similar experience I think it's a bad tube.
stereomaniac
71 posts
 
Call Kevin and get your money back.
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