Additional Preamp Tubes

Just ordered the Premium Matched Pair CV4003/M8136 NOS Mullard tubes. They are Markham manufactured, so while less warm than the Blackburn’s they may in fact be a perfect fit. 

Mitcham was Mullard’s specialized plant for military, industrial, and high-reliability tubes. Consequently, their CV4003s often sound slightly more linear, detailed, and open than their Blackburn siblings. You still get that beautiful liquid midrange, but with a touch more top-end extension, a slightly faster transient response, and a tighter bass grip.

We shall see. Thank you for your advice. 

Amperex 7316 are my favorite, 1950s if you can ever find a matched pair/quad, but most likely 1960s.....these are easier to find and slightly more affordable, and are brilliant. 

I had the BHK preamp for a while and used the tubes mentioned previously, i.e., Brimar, Mullard and RCA.  I tend to like a warmer rather than analytical sound.  I purchased the Mullards when it was easy to deal with the UK.  It was when I stumbled upon and tried RCA black plate triple mica that I was happiest.  It provided warmth, clarity and bounce, allowed the highs to come through but nice and round in the mids and bass, much to my liking.  And, it was around half the price of the others.

I changed my system completely since then, and found the Amperex was a good match after the change.  The good news is there are options, but it's your ears that need to be happy.

If anybody is still listening, you might consider some new production tubes. Ray's Select 12au7 are nicely balanced tubes. I also tried new production Mullards. Currently I am using PSVane Horizons (GASP!) in my Backert Labs Rhythm. If you want a more controlled sound with lots of depth, give them a try. At 65$ pair from Amazon (Gasp again!!) not much to lose. 

+1 on Psvane!  I've had terrific luck with Psvane tubes.  For new production tubes, they come pretty damn close to NOS, (and sometimes better).  Highly recommended.