Where can I get RAM super low noise tubes?

Does not look to me, that the above mentioned article answers Sean's very well founded question. I sincerely hope RM will come back to this thread. He, by the way, was the designer of a wonderful preamp marketed by Beveridge, which a hatchet job review of HP in favour of the SP6 unjustifyably drove off the market and Beveridge into ruin. Cannot remember when that was, must have been in the seventies, It was then, I think, that RM started RAM tubes and his RAM Labs enterprise.

Roger has been responsible for a LOT of very good designs and products. Anyone that has read IAR from the beginning knows his name and would recognize the influence that he's had on the industry as a whole. Let's hope he pops back in and shares some of his knowledge and experience. Sean
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Sean,

Thanks for the question and thanks to Bullwnkl999 for pointing you to my article "Why and Amplifier's sound changes when you change the tubes". I started designing circuits by ear (and my oscilloscope) at a very early age, before I had studied electronics formally. I felt then and still feel now that circuits affect sound more than parts. Yet parts interact with circuits, and that's the rub. As a mature designer, I design so that part variations have the least effect on my circuits. Therefore, you may hear the least variation when you swap tubes in Music Reference products.

In the examples given in the article mentioned above, the changes were both audible and measurable and due to circuits which, in my estimation, are too sensitive to tube variations.

Now, does a certain tube, say the smooth plate Telefunken always sound the same in every circuit? I don't find it so. Does a tube have frequency response properties of its own? Definitely not. Can a tube change the frequency response of a circuit? Yes it can, but it shouldn't, not in a good circuit.

Although we can't fix overly-sensitive circuits, we can screen the tubes for operating parameters such as gain (mu) and plate voltage for a standard bias value. This is better than just a transconductance test in a Hickok as it measures where the tube will "bias up" in a typical circuit. I find that the self-bias point is the most important factor in sound as it affects distortion directly. We have rejected many of the recent 12AX7 variants as they do not "bias up" anywhere near the accepted (RCA, Sylvania, GE, Telefunken) values. As those companies used the same published curves (have a look they are all the same), their tubes biased up to the same point (except for tube to tube variations). So I agree with your last statement wholeheartedly. We keep a tight watch on operating points, and even have customers savvy enough to request tubes from the upper end, lower end or the middle of the range, as they know what they like. Since all the data is on every tube, we can easily pull what they want from stock.

With all this information on every tube, why buy random tubes where you don’t know anything about the noise, microphonics, gain or operating point.

I'll share a little story on noise. When I was visiting the EI factory in Yugoslavia I mentioned to the engineer that the folks at Sylvania (in Altoona) didn't know how to make a low noise 6DJ8, 12AX7 or any preamp triode. It's mostly a function of cathode coating. When I saw how crude the cathode coating technique was, I wondered how a low noise tube gets made anywhere. They just mix this powder up in a bucket with water and spray it on the nickel cathode sleeves. So I asked the engineer at EI how they got such low noise cathodes (theirs are the best I've seen). He said, "Well we don’t know for sure, its not a repeatable thing, we have learned to mix the coating a few days before we use it, it may be the water, it may be that the janitor takes a piss in the bucket at night". Well, they say it’s the water that makes New York bagels the best. Go figure.

Roger, THANK YOU for responding. You have at the very least acknowledged and answered many of my questions. While i have nowhere near the experience or knowledge that you do, it is good to see that many of my thoughts and findings parallel yours.

I see that you find most of the differences in tubes to be due to poor circuit stability. I can see and agree with that ( to a point ). I also noticed that you did mention variances with tubes, especially from manufacturer to manufacturer. Like anything else, I guess that this is to be expected.

As to knowing what one likes in a tube or finding out what to look for or request, i guess that this would vary somewhat from component to component. As such, we are still somewhat stuck with doing quite a bit of trial and error. I would think that, and you acknowledged this, everything hinges on one MAJOR variable. That would be the knowledge and understanding level of the engineer that built the product.

Once one was able to find out the specifics of what they preferred for that component, the service that you offer should come as a GREAT benefit to the consumer. Do you offer "suggestions" to customers as what you think might work best for them ? I do have some tube gear but am FAR from being knowledgable about various brands, production runs, etc...

Having someone that is both a VERY knowledgeable designer and "experienced tube tester" to help us along would make a lot of our lives far more simpler and possibly even less expensive in the long run. Sean
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