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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?
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almarg
8,673 posts
 
Hi Bruce (Bifwynne),

There are a considerable number of differences between the EL34 and the KT-120, some of which I described in my initial post above. However it is still possible to design an amp such that it can use either tube. As I mentioned, some of the PrimaLuna amps are designed in that manner. One consequence of that versatility being, I believe, that all of those PrimaLuna amps are rated to deliver significantly less power than the 100W rating of the OP's Rogue amp, even with KT-120s.

And as I indicated in my initial post above, there are grounds for suspicion that the OP's Rogue amp is not designed in a manner that would make it possible to use EL34s or EL34Bs in place of the KT-120's it is supplied with. It seems that the person at Rogue to whom the OP spoke may have simply been mistaken.

Best regards,
-- Al
bifwynne
2,069 posts
 
FWIW, I just checked the Rogue Cronus Magnum website. No obvious clues that it could switch-hit KT-120s and EL34s.

Al, I don't doubt that some amps like the Primaluna can switch hit, but as stated, not apparent that the Cronus Magnum can.

Btw, the web site presented the Rogue Cronus Magnum II amp. Maybe the original series I could switch hit.

Btw, btw, am I reading the web site correctly ... the Rogue Cronus can switch between triode and ultra-linear operation?? That's kinda cool.

Btw, btw, btw, I didn't know that Rogue is all USA made in Brodheadsville, PA ... not far from the Poconos. My family and I love the Poconos .. great all-year round place.
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joeinid
476 posts
 
Bill_K,

Thank you so much! The info helped.
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stereo5 OP
2,766 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."
stereomaniac
71 posts
 
Call Nick at Rogue back or send him an email and tell him what happened. He will help you out and explain what is going on. Rogue has excellent service and is always willing to help owners put, even if the aren't the original owners. They've always been prompt in answering my questions and usually answer the phone when you call.
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