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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
 

Ok, I just talked to Mike at Quicksilver and here is what he said:

1. The 5751 can be substituted for the 12AX7, but ONLY in the input position. Using it in the gain position will cause the phono pre to not operate correctly. 

2. As I described my issue, he was a little surprised and said that it is an unusual problem to have when using the stock tubes. He went piece by piece through my system checking input/output resistances (all check out). He finally said, "what cables are you running from the turntable into the phono pre?" When I mentioned that I'm still waiting for my Morrow Audio phono cable to arrive, so I'm using a high quality spare RCA that I had lying around for my Reel to Reel across the room, he asked, "across the room? how long is that cable?" 17 ft. Convo stopped there. "oh! the problem is most likely that cable!"

I had no idea how sensitive the MP-500 (and most MM carts) are to cable capacitance. If this turns out to be the problem, I will feel more than a little sheepish. I'll report back, but many thanks for all the replies in any case (I ended up learning a ton about tubes)!

mulveling's avatar
mulveling
2,154 posts
 

1. The 5751 can be substituted for the 12AX7, but ONLY in the input position. Using it in the gain position will cause the phono pre to not operate correctly.

By "not operate correctly" I am sure he means that the RIAA EQ will fall a bit outside of specified +/- error range. It will probably sound quite fine, for the most part, and at no risk of damage anywhere. But sure, it’s best to follow the manufacturer’s / designer’s recommendations here.

vthokie83
1,018 posts
 

Reach out to Brent Jesse. Most knowledgeable guy I know, and carries a HUGE selection of NOS tubes of all varieties https://www.audiotubes.com/

marco1's avatar
marco1
610 posts
 

While some of the more “famous” NOS tubes are still available the quiet ones that are needed for a phono stage generally are not. Most important, make sure you get tubes suitable for a phono stage. Unless you have VERY deep pockets I think you’ll find that most NOS tubes will be too noisy even though they’re advertised or you’re told that they are not.

yogiboy's avatar
yogiboy
5,827 posts
 

@crawfishdaddi I have that preamp. The only tube location that is labeled is the gain tube. Can you please tell me where is the cathode and the input tube position located?

Thanks!

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