What Did I Do Wrong?

09-06-15: Stereo5
Rogue initially had EL34 tubes in the amps and eventually they changed to the KT120's.

I believe the EL34 was used in the Cronus, rated at 55W/channel, but as far as I know never in the Cronus Magnum or Cronus Magnum II, which were/are rated at considerably higher power levels.

If you happen to have a multimeter, after the amp has been off for a good while, say an hour or more, remove one of the power tubes and see if there is continuity (0 ohms resistance, or very close to it) between pins 1 and 8 of the socket. Those are the two pins closest to the orientation notch on the socket, one of them on one side of the notch, and the other on the other side of the notch.

Regards,
-- Al

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.

Note that I referred to measuring between pins 1 and 8 of the socket, not any of the tubes. If there is no continuity between those pins on the socket, per my earlier comments it would most likely be a good indication that the amp is not designed to accept EL34s or EL34Bs. Although if there is continuity it would not necessarily mean that they can be used in the amp.

Without a schematic or other specific information on the design of the amp I have no idea as to whether or not the EL34B's may have been damaged. If I were to hazard a guess, though, just based on instinct and on what I know about the tubes, I would guess that they're probably ok.

Good luck. Regards,
-- Al

"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