What Did I Do Wrong?

"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.

Forgive me, but I find this whole thread bizarre, particularly the OP's statement that:

"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." (** = emphasis added by me.)

Based on numerous past experiences with Kevin Deal at Upscale, he always asked me the amp brand I was retubing. If that happened here, I surmise it highly unlikely that Kevin, who knows tubes and amps pretty darn well, would have sold the OP EL34s for a KT-120 tube amp.

And even harder to understand is that the OP wrote that he checked in with Rogue and they even told him how to bias the EL34 tubes, implying that Rogue approved the switch. Weird.

Perhaps Al, Gary (Hifigeek) or one of the other electronics techies can help me out here. I would have thought that an EL34 amp would employ a very different circuit topology than a KT-120 amp. In short, I surmise that the two tube types are not electrically compatible.

Ok, I just embarrassed myself by delving into tech stuff I know knowing about. Go ahead tech guys and slap me down. I deserve it.

Btw, ARC performed the SE upgrade to my Ref 150 several months ago. Kal mentioned in passing that the 6550, KT-120 and KT-150 tubes are electrically similar. Not to say one should just drop a KT-150 tube into an old 6550 tube amp without first checking with the manufacturer. Just making the point that the 3 tubes just mentioned share similar electrical characteristics and properties.

BIF

Just caught the 9-6 post from Mofimadness ... well yeah. If Kevin said don't do it, why would the OP go against Kevin's recommendations.

I surmise that if the Rogue amp works with the KT-120s back in place, then everything is probably ok. But I gotta tell ya, if I shoved EL34s into the tube sockets of my Ref 150 SE, I'd have a lingering concern that I damaged the amp.

Very odd thread.

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

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.