NOS Tube Recommendation for Quicksilver Phono Pre Amp


I recently upgraded from the onboard phono stage in my Technics 1500SL to an all tube Quicksilver Phono Pre Amp. I’m about half way through the 30 hour recommended break-in period and so far, there is a lot to like about this piece of gear: Much thicker/more pronounced bottom end (I’ve had to readjust the gain on my subs quite a bit) and much wider/more defined sound stage. However, because I’m also running an all tube integrated amp (Raven Audio Osprey), there is now a very noticeable "warm" coloration to the music that wasn’t there before. I don’t want to give up on my new phono stage, but it’s like I’m listening to music with a wool blanket over my speakers. I’m thinking rolling the tubes to something a little cleaner/brighter could give me the best of all worlds. There are 3 tubes in the circuit topology: 2 12AX7s (one input, one gain) and 1 12AT7 (cathode follower). I’m currently considering a matched pair of Raytheon JRP black plate 12AX7s and either an RCA or Telefunken for the cathode follower (all NOS). Any and all suggestions/inputs are very much appreciated! P.S. my speakers are Raven Audio Corvus Reference Monitors and my current cart is the always amazing Nagaoka MP-500.

crawfishdaddi

@skiznfliz & @crawfishdaddi 5751 are not a drop-in substitute for 12AX7--thats circuit-dependent, and a phono circuit theyre almost never a substifute for 12AX7. quicksilver will tell you if 5751 can sub for 12AX7 in their phono stage. 

Good thought @cey , I ran a quick search of Audiogon and found this:

https://forum.audiogon.com/posts/2446823
 

sounds like 5751s are interchangeable, but I’ll follow up a with a call tomorrow. 

most tube enthusiasts dont know enough to know that that is incorrect, @crawfishdaddi

to be clear, 5751 is not a drop-in substitute for 12AX7 . that particular substitution is circuit-dependent. its rarely the case in a phono circuit.

glad to clear that up.

ceylon

If I'm wrong please correct me.  The 5751 has lower gain than a 12ax7, but the are otherwise interchangeable.  As such either one may or may not be an optimal choice for a particular circuit design, but they will work.

Yes, it has only 70% of the gain of a 12AX7.  Aside from reducing gain, if it is used as part of the equalizer circuit, that lower gain could screw up the equalization curve and mess up the sound that way.