Rogue ST-100 Tube Rolling

I've owned two EL-34 amps. It was hard to find new production tubes that wowed me. The GL KT77s were recommended to me and they were so much more lively than EL34s. They had smooth extended highs with great dynamics, and clear open sonics. They're not tubey or coloured, but present realistic tonal qualities.

When I upgraded to an EAR Yoshino I rolled in 8 KT77s. This amp was being held back by the EL34's. Now there was clarity and realism with terrific detail in the highs.

That's my story.

my RM-9 thrives on RAM EL-34 E Euro production w impeccable grading, screening. RAM tubes ;-) RIP Roger

Try calling Andy at Vintage Tube in Michigan, he is a wizard with exotic nos.

I am a dusty tube Robot

Your speakers are efficient so you can afford to go down in power. 6L6 are the sweetest tubes. New Tung Sol 7581A are wonderful. 20 hours burn in.

Tried other tubes- made me appreciate  just how good the KT120s are. 

Hi Guys, appreciate the insight, has me doing some different research. As you can tell I am not an expert in the area.

Another question, back to my initial premise. Since I have High Efficiency speakers, have already rolled the smaller tubes, listen at lower levels, and like more the separation of instruments (the space in between).

- Does it make sense for me to be looking for a different power tube than the KT120?

- Does it make a difference I barely move the volume control?

I’ve tried KT120 vs EH KT90 in Rogue Apollos and KT120 vs. KT88 Gold Lion and KT150 in VAC amps. Yeah, I just always go back to KT120, which sound more musically balanced to me in all cases. In the VACs, they get progressively darker and bass heavy from KT88 to 120 to 150, with 120 being the right mix. In Apollos the EH KT90 were a touch bright. That said lower power tubes like 6L6GC, 7581, 5881, and EL34 have sounded super sweet to me in other amps, but I’m not sure how suboptimal they might be in the Rogue amps. Back when I had an Atlas non-magnum I wasn’t really impressed by its ability to tap into the sweet tone of vintage EL34 tubes. It was OK, but an Eico HF-87 did a much better job of showing off the nuances of each vintage make. The Atlas kind of homogenized them all. And the Stereo 90 with EH KT90 sounded outright better. I am "sort of" interested in trying the Tung-Sol 7581A though. I’ve loved vintage GE 7581A in old Heathkit W5 amps. And the KT77 Gold Lion are still an interesting option - but getting TWELVE of them (Apollos) has kept me away.

12ax7 is usually the key spot to roll but if you’ve already tried Telefunken smooth plates, those are good ones. You can get a bit more zing, kick, and dynamics with a ribbed plate Tele or especially a Mazda silver plate. You might also try some triple mica black plate 5751 for a more focused, precise sound with better separation. 12ax7 generally gives a bigger, bolder sound. The Mazda silvers give both but if you look at the plate structure (ignoring the shiny silver color) - they look like most American 5751, lol. 

Next you can sub 12bh7 in for the 12au7 slots, which I think is a really really big improvement across the board (I hate 12au7), but Rogue won’t officially sign off on that sub anymore (Mark told me it was OK, in the past). I ran Apollos for almost 10 years like that.

And finally you can up the bias to at least 45 mA on those KT120, which are loafing at 40 mA in these Rogue amps :) Do the math - if 40 mA is OK for a KT88 with 42 Watt plates, then that’s analogous to ~ 58 mA on a KT120 with 60 Watt plates (don’t go that high though lol). I’ve heard of guys happily going up tp 50mA, but proceed at your own risk there.

Try that all together: 12bh7, 45 - 50mA KT120, and 5751, and you will be shocked at the difference!