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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 11 responses by stereo5

stereo5's avatar
stereo5 OP
6,254 posts
 
I went through all of that. It was distorted sound and no reading at all on the bias meter. The kt-120's I put back in biased fine after that.
stereo5's avatar
stereo5 OP
6,254 posts
 
The range on the bias meter is 0 to 100ma.

The KT120 tubes use 35 ma and the EL34 tubes use 30ma.
stereo5's avatar
stereo5 OP
6,254 posts
 
09-05-15: Analogluvr
So u got a reading fine with the 120s?

Yup, everything is fine with the KT120 tubes back in.
stereo5's avatar
stereo5 OP
6,254 posts
 
May explain the OP's findings in his system!

Wrong.
stereo5's avatar
stereo5 OP
6,254 posts
 
Rogue initially had EL34 tubes in the amps and eventually they changed to the KT120's. Nick at Rogue Audio told me they will work fine and to set the bias at 30ma. That's all I know.
stereo5's avatar
stereo5 OP
6,254 posts
 
Almarg

Are you talking the KT120's that are in there now or the EL34B tubes which I removed already? Do you think the EL34's are toast? I should have listened to Uncle Kevin at Upscale, he advised against it.
stereo5's avatar
stereo5 OP
6,254 posts
 
The tubes were already on route to my house before I talked to Kevin at Upscale. My only reason for contacting him was because I had received a partial refund for the order. I had ordered the tubes be cryoed and paid the 8.00 per tube. When I got a 32.00 refund, I then called Kevin. During the course of the conversation, I mentioned the Cronus Magnum and he said he wouldn't do it. When I pointed out that Nick at Rogue said it would be ok, he then said "go ahead and try it."
stereo5's avatar
stereo5 OP
6,254 posts
 
I already sent Nick an email and stated I would follow up with a phone call tomorrow.
stereo5's avatar
stereo5 OP
6,254 posts
 
Talked to Nick at Rogue today and he confirmed the EL34 tubes do work in the Cronus Magnum. He said I may have to turn the bias pots up to a dozen turns to get the tubes to bias.
stereo5's avatar
stereo5 OP
6,254 posts
 
I put the EL34 tubes back in today and set the bias. It is now rock steady at 30ma as per Rogue Audio. It seems the EL34 tubes needed a dozen turns each on the bias pots. That did the trick. I never would have thought I would have to turn the bias pots that many turns for this tube.

It is thanks to a fellow Audiogoner that I had the courage to try this again and the results are stellar. I am really liking the EL34 sound.
stereo5's avatar
stereo5 OP
6,254 posts
 

I sent you a PM.


No, the Cronus Magnum is long gone now.

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