Questions about tubes and their subsitites

For some reason, I swore I'd read that the 5814 had 70 db gain but I am obviously wrong. It does make more sense now. I have used Sylvania GP 6189's and still have them. I have a pretty fair collection of vintage tubes.

Next question is alittle more weird. I have a very low output MC cartridge. Fidelity Research FR1MK3F which has .14 mv output. I use an SAEC SUT, which only provides 10db of gain. I have often thought that I'm still a tad low in gain for this cartridge so I tried an experiment. I put a second pair of Sylvania Gold Pin 5751's in the AU7 spots. 

This obviously provides more gain and to my surprise, it sounded very good to my ears, and to my wife's as well. Everything seemed to sound better than it should. My system has undergone many changes over the past few months as old pieces began to fail and I inserted multiple new (used) pieces into the system and would evaluate each with mostly disappointment and a few pleasant surprises. Things may not be perfect back to where I started but it has become very pleasant to sit and listen. I've gone through half a dozen preamps or more, 2 turntables and several cartridge tries. It's been fun and frustrating at the same time. 

Anyway, the question is this: Am I hurting anything by having 5751's in the Cary where it was designed to have 12AU7's?

Thanks,

Bill

I doubt that you would hurt anything. But just to make sure you should ask Cary if it is okay to do that. I swap preamp tubes in my phono preamp to lower the gain and I never had a problem. It never hurts to ask the manufacturer!!

I am also using lower gain tubes at the 12AX7 spots, using 5751's which are 30db lower than what it calls for. 5751's are often used this way and many favor them, including myself. I have never found any AX7's that sounded  better than the various 5751's that I've used, my favorites being the Sylvania Gold pin 3 micas but there have been others that were good such as RCA clear tops and a few others that I've tried were good.

I've tried a multitude of different tubes in the AU7's spots, including Bugle Boy long plate AU7's, which are considered among the best. In my situation, they were OK but I didn't find them to be "great". Many factors involved here, many different preamps etc.I'll give them a try again at some point as I'm on about the 6th or 7th, preamp in this system. The Cary has been used in nearly every situation as I've found nothing better or even nearly as good.

At any rate, I'll see what Cary says. I think they recommend against such things but my personal belief is that it is unlikely to actually cause any harm, it's just very curious that things are sounding so good. It's been the best combination I've found with all the reserve pieces that I'm using. My main turntable is down as well as my main preamp. It's been an interesting journey and I've found some pleasant surprises along the way. I shelved this preamp 25 years ago. Loaned it to my son many years back, got it back and tried it after all the pieces that I bought in between. Kind of funny really. 

I have used Sylvania /Baldwin green label tubes and they are outstanding. I am now using GE 12 type and 5751 tubes in all my gear and I won’t be replacing them. I like them a lot!

I just got a batch of 5 Sylvania 3 mica 5814's to see what I think of them. I have not tested them yet to make up pairs. After I do, I'll see how they compare to the Gold Pins. I've never really been disappointed by any Sylvania tubes. I have a pretty good collection of Sylvania, RCA, Amperex and others. I do have a fair amount of GE's. I'll have to check to see if I have any of their 5751's but I don't think I do, probably just have AX and AU7's. They were fine when I used them, I just found the Sylvanias more to my liking. I'm sure this stuff varies a great deal from one component to another. I don't think there is any way to make cheap Chinese tubes sound good but I'm sure really good tubes will vary from one component to another. 

Also, wrote to Cary to see what they have to say about my experiment. I've noticed that for a serious listen (which is pretty loud), I've gone from 12 or 1 o'clock to 11 o'clock on the preamp volume. I may remove the SUT just for kicks to see if it gets better or worse. At 11, with no record spinning, I hear a slight tube hiss so I may be close to where I need to be even with the SUT. Only way to figure it out is to try both ways.