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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

Showing 3 responses by mofimadness

mofimadness's avatar
mofimadness
4,152 posts
 
From the manual:

TROUBLESHOOTING

Tube will not bias:

If the meter provides a reading but the tube will not bias, the tube is probably bad. If no meter reading can be attained, check the fuse (1/4 Amp slow blow).

If the fuse is bad, replace the fuse and then set the bias.

If the bias will not maintain itself and the fuse blows again, the tube should be replaced.

Bias Meter reading is too high:

Check that you do not have two of the bias switches
turned on.

Output sounds distorted - Check the bias on the output tubes to ensure that the tubes are operating properly
mofimadness's avatar
mofimadness
4,152 posts
 
"I should have listened to Uncle Kevin at Upscale, he advised against it."

I have known Kevin for almost 30 years and have bought thousands of dollars worth of tubes from him. I have never had a bad one and he has never steered me wrong with his recommendations.

If he advised against it, you should have listened. He knows more about tubes than anyone I've ever meet.
mofimadness's avatar
mofimadness
4,152 posts
 
Stereo5...please let us know what you find out. I'm kinda intrigued by the problem.
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