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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
crawfishdaddi OP
38 posts
 

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. 

cey's avatar
cey
362 posts
 

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

onhwy61's avatar
onhwy61
5,440 posts
 

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.

larryi
4,590 posts
 

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.

crawfishdaddi OP
38 posts
 

@larryi @cey , this is great stuff (insights like this are what I was hoping to find when I posted this question). Quick follow-up: if I decided to go with 5751s (several people have reported these clean up the sound in their phono stages), is there a particular position I should avoid so that the RIAA equalization curve isn't disrupted (I will ask the same question when I call Mike over at Quicksilver today and report back)? My current thinking is to put the 5751 in the gain position, and just roll the input and cathode follower tubes with NOS tubes (same tube type).

I'm thinking GE triple mica 5751 for gain, Rayethon/RCA 7025 12AX7 for input, and Telefunken/Amperex Bugle Boy 12AT7 for cathode follower... Also, once I go with a 5751 in the signal path, do I need to make all of the tubes 5751 because of the lower gain?

thanks again

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