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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
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.
joeinid's avatar
joeinid
476 posts
 
Can anyone please tell me the difference between the EL34B and the regular EL34? I'm curious.....
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