NOS Tube Recommendation for Quicksilver Phono Pre Amp

@crawfishdaddi 

OK, now I see you have stated the result seems a bit too warm. So you want something with a bit more "zing". In that case, you should check out the following:

• Mazda silver plate 12AX7 (expensive)
• Telefunken ribbed plate 12AX7
• (Russia) new Tung-Sol 12AX7

Electro Harmonix 12AX7 are fairly bright. I usually don't like them, but they can certainly counter warmth. Later Sylvania 5751 were also pretty bright, and I didn't like them - but who knows, here. 

RCA are weird - most are warm but some of them have been unbearably bright (and those tubes have been from Andy @ VTS with the cleaned pins; wonder if that's related).

If a phono stage has a strong "voicing" on its own, you are not going to fully counteract it with tube rolling. 

thanks @mulveling  -great stuff!
I've never actually seen the fabled Mazda silver plate 12AX7 for sale anywhere... I'm starting to think it's only a myth. 

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)!

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.

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/