Coincident Frankenstein mk.2 amps

@charles1dad Thank you.  In addition to what I described above, I can say that I never thought I could achieve this level of detail, drive, realism.  The sound is incredibly engaging, more so now than ever.  

The Mullard you are using is the CV378?  Mr. Blume wrote in the manual not to try tubes other than the 5u4gb, but he suggested the CV378, so I am a bit confused.  I have also read that the KR tubes were somewhat unreliable.  

The Supremes are amazing.  The DWs could get a bit etched or strained at times.  The Supremes are smooth on the highs, relaxed but extremely detailed.  The sound is fuller and it I feel it is more coherent from top to bottom.  Placement is very important.

What is my goal with replacing the tubes?  I really don't know, but I am always looking to improve the sound.  Being surprised by some new sound is something I enjoy immensely.  

tswista,
I’m using the Mullard CV 378 and as I wrote earlier there haven’t been any performance or reliability concerns. This tube and/or the 5u4gb will serve you very well. .

The KR XLS was loaned to me and as stated had excellent sound quality. I know that some KR tubes have had reliability issues and I don’t know the status of current production. I am not sure if this issue involved the XLS 300b. The early production Elrog 300b which I owned had durability problems (I had 3 pairs fail after only 4 to 5 months of use). Elrog has new ownership x about 2 years and are said to be very reliable now. I hope this is true as it’s a superb sounding tube.

The EML XLS 300b has earned a reputation for extraordinary durability and an exceptionally long lifespan. Some of their earliest versions that have gotten very heavy use are now approaching 40,000 hours without failure. This is an outstanding result. I believe that the Frankenstein can be a bit tough on 300bs but seems to present no challenge/problem for the EML XLS. I tried the EML mesh plate (beautiful sound quality) but it failed after a couple of months. It needs to be used in an amplifier with lower operating points than the Frankensteins.

It makes me happy to know that you’re getting "incredibly engaging" sound quality and realism with your Frankensteins/Soul Supreme pairing. I completely understand how you feel. Amplifiers really thrive with good quality high impedance easy load speakers (As atmosphere has  pointed out numerous times on this forum). Who knows, you may not ever return to the high power amplifier/low impedance difficult load alternative 😊.
Charles

I ordered a pair of Mullard CV378s from Mr. Blume.  For good measure, I also ordered a pair of vintage RCA 5u4gbs.  When I scrape together the funds, I will either order a pair of Psvane Black Bottles or the Acmes, based on his recommendations.  @charles1dad I can tell you right now, that I am never turning back.  This may sound cheesy, but this path that I have finally come across has been a life changing experience when it comes to music reproduction.

@charles1dad  From what I understand, there are not many 6EM/A7 choices around.  I dropped in some NOS GEs and they were SUPER hot on the high end.  Almost unlistenable.  The amp came with RCAs.  Before I order a few backups, I wanted to see if you had anything to add.  Thank you.