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?
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Showing 2 responses by daveyf

Sounds like these tubes are preferred in the pro audio setting, to be utilized in a guitar amp! There the ability to fall into distortion quicker would be a value. The exact opposite of what we want in the audio world.
As a guitar player, that's the kind of tube I would search out for my amp, something that can add some distortion and tone without me having to push it too hard. May explain the OP's findings in his system!