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Looking for advise regarding Rogue M180’s

  Last week a friend gifted me a pair of Rogue M180’s. They were sold as 180’s and I received them from the original owner. Im guessing them to be 10-12 years old. They were used when first purchased for about 5 years sparingly. Since then they have resided on a flat dolly in a spare bedroom. The amps still have the original Phillips ECG 5751 and 5814A’s installed. The original EH KT 90’s are loose in a box with an octet of low hour Gold Lion KT-77’s . Years back when in use the owner contacted Rogue and stated they were too powerful for his room size and speaker selection. Rogue responded by recommending the GL KT77’s and suggesting that he could also lower the bias from 40ma to 30ma. I was provided the supporting emails dated September 2019. Here is my situation followed by my questions. I currently have a low power single ended system with Zu speakers. Second,  the owner stated one might have a hum, but was not sure. He’s on his second complete system since and has a room full of gear he’s lost interest in and his memory is vague. Also back then he had power issues with his provider and stated they installed a new transformer on the street. So my questions are first, checking for any hum. My intent is to take a single amp and connect one JBL 4312 to it. Install the KT77’s, plug it in and listen for a hum and bias the tubes. Do I need the input open or shorted ? Or something else ? Second, the 12AX7’s being replaced by the 5751. I see there’s a mu of 70 Vs 100 with the 12AX7. Does that effect the overall output power of the amp or just change tone and distortion? FWIT I have 6-7 pairs of NOS Telefunken 12AU7’s but zero 12AX7’s. My intent is to check for hum without causing any damage. If a hum exists, I’ll ship to Rogue. In the short term if I’m successful, I’ll test drive with my existing Rogue RP-1, the JBL 4312A’s that are mint and the 26” Sound Anchor stands I have with them. And I’d like to get some Telefunkens to put in the 12AX7 positions. After that, there’s a pristine Rogue Hera that’s been inspected and re tubed  by Rogue that I’ll ask to purchase before I start looking for speakers worthy of the pairing. Also I emailed Rogue for support a week ago and have not received a response. Thanks in advance for any feedback and my apologies for grammatical spaghetti, but I’m limited to an IPhone. Cheers , Mike B. 

buellrider97

Showing 3 responses by jafox

jafox
1,467 posts
 

Congratulations on such an exciting gift. I have read a lot of positive comments on the Rogue amplifiers on these forums. Finally, the curiosity got the best of me to try one of these out when a good deal was found on the Apollo Dark monos.

I was a long time user of the CAT JL-3 mono amps. These throw out a lot of heat. And with the huge number of tubes, they are costly to maintain every few years. I have heard nothing in my system, tube or SS, that comes even close. But finally, I found a SS amp, the Symphonic Line (SL) Kraft 300 amp that is truly impressive. The SL product line is quite special. It does so many things beautifully, but the CAT amps are in a different ballpark, in dynamics, clarity and openness. The CATs are not tubey-sounding amps. I’m sure these 20 year old amps still hold their own against all the latest ARC, CJ, etc., of today.

I have been running the SL Kraft for about a year with great success and only two issues: 1) the SL amp sounds horrible until a long warmup, many hours to a day, and keeping it on all the time gets pricey! ; 2) I miss the "magic" that comes with a tube amp. Enter the Rogue amps.

After living with the Apollos for two weeks, I can share some setup details. Mine came with TungSol KT-90s. They came with Amperex 12ax7, and unknown 12au7’s. A number of years ago I spend a lot of tube rolling to find the coveted triplet (12ax7, 12au7, 6922) for the CAT amps. Replacing the Amperex with the 5751 (I can’t see the brand on the glass) I had used on the CAT was significant; there was a bite in the upper mids/lower trebles that was gone thanks to the 5751. The sound was good but I had one more test - replace the 12au7 pairs with my all-time favorite here - the RCA 12BH7. Every time I have used this tube in 12au7 sockets for DAC, Line Stage, amps, it always reigns supreme and it did not let me down here either. The mids were much more smooth with greater decays. After an hour or so, I was so impressed for the value of these amps. They locked onto the SoundLab A1s incredibly well. I use the 8-ohm terminals as I always have when I had a choice.

With all the success, I had/have some issues that I did not have with the SL Kraft or the CATs. With the Apollos, I suddenly had a ground-loop hum. I have three circuits in the room, one each (different phases) for when I use the cat amps, and the third for the rest of the system. I never had hum issues with this. Using the SL amp’s both power cords into a circuit on the opposite phase of the system never caused a problem. But this same setup caused hum out of the right speaker with the Apollos. I changed to my backup power cords and the problem was gone. Back to the first cords and the hum was back. I fussed with cable routing, cable lifters, etc. Finally I threw in a cheater plug and the problem was resolved. But I don’t like to have to do this. So you might need to be extra careful with cable layout, cables crossing/touching, circuits, phases, etc.

With the Apollos, I have more tube noise vs. with the SL amp, but once the music starts, you can’t hear it. And I tried the Triode mode. This was quite disappointing as I expected an even more lush sound, but it was too mellow and the strong bass foundation much diminished. So you can play with that switch as well to see what mode works for you.

I am back to a fully tubed system. And I have to say that I love it. Enjoy the 180s.

John

jafox
1,467 posts
 

@buellrider97 - I goofed.  No idea why I entered KT90 tubes above.  The Apollos came with 12 KT120 TungSol tubes .  I saw a tube site a couple weeks ago with a great sale on KT88's.  But I thought I'd enjoy the Apollos for awhile before I look to compare other power tubes.

Find a preamp with the sound you like rather than worry if it is balanced or not.  And the IC that you use between the preamp and the M180s will greatly determine whether you hear the amps' capabilities or not. 

jafox
1,467 posts
 

@buellrider97 Happy to hear of your communications with Rogue.  They got back to me quickly for the three times I had questions on the Apollos.

As for paying for the Dark upgrade, compare the cost of updating your amps to Dark vs. selling your amps once they are running well, and seek a good deal on a used pair of Dark.  Here is one example, from a dealer no less.  Notice the Make Offer option.

https://www.audiogon.com/listings/lisba80c-rogue-audio-m-180-dark-monoblock-amplifiers-black-very-good-condition-tube

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