Seeking a Warm 12AX7 Tube for Preamp

@spacecadet65 I bought a bunch of 12AX7, 7025, 5751 and 12AT7 NOS and a couple new production variants to replace a stock JJ 12AX7 that I also found “bright and strident” in a Willsenton R800i 845. The R800i uses one 12AX7 as the V1 signal tube in the preamp section so it has a noticeable impact on tone not withstanding a GFB design. 

The clear winners for “warmth,” which I would describe as enhanced bass response and rolled off treble are the RCA and Brimar black plates. The RCA is the much better of the two, the Brimar is smooth and warm to the point of sounding a bit mushy with lack of detail. The RCAs are warm, smooth and retain detail. A real stand out in my rig is the Raytheon black plate, it is warm yet linear with no high roll off, strong bass, clear airy treble and neutral yet present midrange and superb soundstage depth. Can you tell I really like it!? 

Of the remaining lot, in order of neutral, transparent to detail and airy I’d rank as follows:

GE

Mullard

Telefunken

Gold Lion gold pin from Russia

Sylvania 5751 black plate

RFT

Amperex Bugle Boy

My three favorites are the Raytheon black plate, Telefunken smooth plate, probably the most balanced linear and neutral of the bunch without losing any details, and the Amperex BB. The Amperex is in a class of its own for airy details and a much higher soundstage. The Raytheon has depth and detail with punch, the BB has more detail in the higher frequencies and the soundstage appears two or three feet higher. It’s a great jazz or modern well recorded Indie track tube. 
 

The biggest disappointment is the Mullard. Everyone raves about them online, but in my system, it is just average. Balanced, yes, linear, yes, but nothing special. 
 

It’s possible some of the strident edge is coming from too much gain. You might consider rolling in a 5751 or even a 12AT7 depending on speaker sensitivity. Just a thought.

Cheers,

@spacecadet65 (love the name btw), if you picked up the triple mica black plate GE 5751, you've got a real winner, I have one of those as well.  I also have a couple regular GE 5751 grey plate, they're pretty good too with a neutral, linear "softer" sound signature. 

If you're volume pot is 9 o'clock and 90 dB speaker output, something is running with high gain.  You could try attenuators on the amplifier inputs.  Initially I could not get the Willsenton volume past 9 o'clock, 10 max with 99dB sensitive Klipsch Fortes.  With 10dB attenuators I can now use more of the volume pot, the VU meters move more than a centimeter or two and no loss in sound quality, dynamics, rhythm pace or timing. Check out Parts Express, they have Harrison Labs in-line attenuators for RCA inputs.  You can also find XLR attenuators if you're running fully balanced interconnects. 

Another thing to consider is "tube synergy." What are the other tubes in the pre-amp circuit?  The next stage in the Willsenton is two 6SN7s each driving a 300B which drive 845 output tubes.  I've found mixing and matching the 12AX7/5751/12AT7 with certain 6SN7s can also make a sonic difference. 

My favorite 6SN7 in the Willsenton are Tung Sol WGTA brown base JAN.  Great combination of warmth, lots of detail and punch.  Sylvania WGTs, WGTAs and WGTBs are more mellow, less detail but have a lot of warmth.  RCAs are smoother, less detail, less warmth, but very neutral, linear frequency response and can stand a "hotter" 12AX7 to punch them up a notch.  Raytheon WGTAs and WGTBs are a touch grainy, think guitar amp in overdrive, and marry better with a softer V1 like the GE 5751 or a Telefunken 12AT7.   

I probably spend too much time swapping tubes in and out, but that is part of the fun of a good tube amp I guess. 

Oh it’s a rabbit hole for sure! I’ve ended up with four tube amps, one tube/SS hybrid and a collection of over 250 vacuum tubes. The tubes will outlive me AND my children! Unlike my wine cellar which always seems low, wonder why?

BTW, rolled in one of the GE 5751s last night in front of Raytheon GTB listening to Beth Hart’s new release.  Very relaxed, smooth and warm presentation with plenty of detail.  I think you’ll really like the GE vs the strident JJ.