Try the lower gain version of the 12AX7 as a 12AU7 sub, know as 5751.
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The 5751 has a gain of 70 compared to the 12au7 gain of 19. I've never heard of using that in place of a 12au7. I do replace 12ax7's with them and like them.
As far as low gain 12au7's I don't know of one. Someone may give recommendations for a tube to try. If not you could put a simple two resistor voltage divider network on the input to your amp.
Are you sure those are preamp tubes? Mastersounds claim to fame has always been their passive gain stage. The 12AU7 tubes are drivers for the output tubes. Using one of the low gain alternatives will result in a very dull sound.
Apparently yours is a CD based system. What CD player are you using? Do you know what the output voltage is? If you want to cut back the gain someplace the source may be the best place to do it. The other alternative is a less efficient speaker.
I'm no tech. expert, but I always thought the 12AU7 was designed as a "unity gain" tube. Meaning it does not provide gain at all. Usually used at the end of a preamp as a cathode follower to improve that circuit's ability to drive the cable and the next amplifying device. By experimenting you will probably find another 12AU7 that you " perceive" to have lower gain.
I guess I'm just looking for a smoother tube with a "Perceived" lower gain. I'm using a TT with a cambridge 640p on MM for my input.
I guess I'm just trying lower the gain of the whole amp. Seems to be a hiss running through the speakers, even with the volume off. Cd or TT doesn't matter. Unplugged all accessories, doesn't matter.
Maybe I just shouldn't be trying to run this amp with my La Scala's. Higher volumes sound amazing!! Lower, I get a hiss.
"A simple solution to the gain issue is to use an attenuator between your CD player and the input of the Mastersound"
Yes thank you. That's not the problem though. I unplug all my accessories. Just the amp and speakers hooked up, thats all, and the hiss is still there.
It doesn't change at all when I turn the volume knob all the way up, no feedback noise(as per the amp specs!) just the same steady low hiss.
I'm just guessing now that it's that the La Scala's are too efficient, even at idle they'll have a small hiss with this amp.
I'm also guessing that swapping tubes isn't gonna change anything from the posts I'm getting here.
Oh, well. It sounds Excellent at higher volumes! I will have to just ignore this one issue that my new amp has introduced to my system.
The zero negative feedback still really blows me away....
Then you have asked the wrong question. You just need quieter driver tubes, not lower gain tubes. Tubes vary quite a bit in the amount of their ambient noise. You just need tubes that are selected for low noise. They are available from most dealers. Many of us, myself included, use tube amps with Klipsch speakers and have minimal issues with noise.
I'm Sorry for asking the wrong question.
I want my amp to be less noisy in the hiss department.
Where can I find tubes that are selected for low noise?
Do you think that it could be that the EL34 power tubes are too noisy as well, or probably just the preamp tubes?
In my current setup I'm running 2 JJ ECC82 Gold pin tubes for the preamp, and 4 SED Winged C EL34's in the power end, on a Mastersound Due Venti through Klipsch La Scala's.
If I can find some low noise tubes, is there any particular brand or model that someone with a similar set up would recommend?
Thanks to anyone that can help......
Roger Modjeski at Ram Labs sells low noise tubes. Follow the link:
I've had much better luck buying from him and Andy at Vintage Tube Services than Upscale Audio.
I suggested that you speak with Jim because he is very candid and has a great deal of experience. There is another option that you should speak with a good tube monger about and that is the ruggedized, industrial grade, 12AU7s that are less microphonic than the standard breed. My favorite is 5963 but 7189 and particularly 6680 are other industrial direct substitues. They will still need to be graded for noise however. I am somewhat less than sanguine about my RAM Labs tubes, but that's what makes horse racing.
A friend lent me a 300 BPSE I think it was (24 watt 300b) and it was such a beautiful amplifier. I don't remember anything but a black quiet noise floor and beautiful blooming music with that amp.
Is it something you notice during playback or is it something that bothers you in some other way? I second the Andy rec but just take your time waiting as order to ship time is s l o w.
On another note I've heard the Trienta with all Valhalla and a Thor conditioner and it was extremely clean and clear with stock tubes. In other words maybe look at something other than tubes??? Cell phone near by, modem, lighting, computer plugged into same breaker, etc..??
I've found el34's- the Winged C, actually, to be "noisy", with a hiss at idle even with the volume turned all the way down. That, however, was on a Golden Tube Audio amp, which don't have the best build quality. MastersounD is in a different league.
I don't know if it's your drivers or the power tubes. What I do know is that MastersounD amps don't usually do this sort of thing- they are of high quality. My Compact 845 is dead quiet with 97 db/w/m speakers.
What I can do to help rectify the issue is this- I don't use the preamp section on my Compact 845. I use it as a straight power amp. Hence, I took the preamp tubes I bought for it- Telefunken smooth plates- out and tossed the Electro Harmonix back in the amp. No sense running the Telefunkens if they're out of the circuit.
So....if you want to try out a Telefunken 12au7 and see if the hiss goes away, let me know. Fire me an e-mail through Audiogon. You can try mine. If they work, great, you can then get a pair yourself and send mine back. If they don't eliminate the hiss, send them back to me, knowing they're not the issue. When I did use the Compact 845 as an integrated with the Telefunken tubes, it was dead quiet. No hiss. So, I know these NOS tubes are not defective. Let me know.
Follow up number 2!
Destroyed all 4 SED EL34's in the amp. The bias was way too hot when I got it and I never checked, thinking it was auto bias. Every tube was red plating with in a week.
Contacted the Italians and they were kind enough to show me how to bias this older "Semi-automatic bias" amp???
They sent pictures and everything. Very nice people.
Bought a matched quad of the EH 6CA7s last week, biased them to "no more than 6VDC" (I'm still not sure how this stuff works...)
Everything sounded beautiful. Way better.
The hiss was cut in half as well.
Then I ended up finding a guy on eBay from Moldova selling NOS RFT ECC82s matched pairs for $10 a tube...(sketchy?)
Many people on tons of threads recommended these German made tubes as the quietest tubes you could find and one of their favorite 12au7s for detail and value.
Got them today, plugged them in and Wow!
I can turn the amp to top volume and I have to stick my ear right into the squawker of the La Sacala's to even hear a slight buzz.
And for detail, they blow the JJ Golds away! Even after just a days listen.
Maybe I'm just too excited about the whole thing and posting too soon. But I PRAY that things stay this way!!
Thanks very much for all the help you guys!
Very Very appreciative!
Thanks to Viridian as well for lots of good advice keeping me a little more sane.
Derek, thanks for the heads up, I often get my hookers and Viagra from Moldova, but never thought of getting tubes there.
In all seriousness, it's so great to correspond with someone that has had some issues with their first tube experience and works through it in the spirit of a greater connection with the music. Tube gear has a reputation, in some quarters, of being unreliable, and that is because, as you have learned, there needs to be a small amount of knowledge and involvement from the owner. But once sorted out, my experience is that tube gear is at least as reliable, and oft times more reliable, than solid-state. I am glad to see that you are finally enjoying the fruits of your labor.