Audio Research SP-10 6922 or 6DJ8

The electrical characteristics are close enough that the 6DJ8, 6922 and 7308 will all three work in the ARC circuit. There is one other possibility, the 7316, which is very low noise military version, also electrically similar to these other three. If you want an ultra clean and linear sound, try the USA Amperex 7308, especially the CEP version. Somewhat less linear and more warm would be the Dutch Bugle Boy 6DJ8, or the Mullard 6922. The Siemens 6922 CCA is a very detailed and low distortion tube, but is less friendly to bright recordings with the ARC. You did not say what you were listening to right now, and if you were happy with the tonal balance and dynamic range provided. I and others here can probably advise you, given that information, and what you like and dislike about the sound right now.

I owned an SP-10 for 8 years in the 80s and found the RAM tubes to work very well. In the later years these were 6922. When I switched from the older 6DJ8, the sound was less noise and more resolution but I did not know if this due to newer tubes or the new tube type. I typically replaced the tubes in the phono stage every year and ALWAYS went with the lowest noise tubes as possible. RAM Labs had a special series of low noise tubes. I then rotated the existing phono tubes into the line stage. It was just too costly and I think unnecessary to replace the entire tube set very often. But the phono stage was very sensitive to tube noise. ARC has come a long long way since then to make lower noise preamps, but only a few models since then have had the musical involvement and magic of the SP-10. Hope this helps a lot.

Thanks to both of you for your advice. My SP-10 MK 2 posessed the most perfect midrange phono reproduction I had ever heard.....until my phono (4) tubes went. They were big bottle 6dj8s marked with no name, except "made in USSR" The sound was big, lush, 3D bigtime! and no brightness. The plates on these tubes were extra wide. Tried the ARC preferred Sovtek 6922 and was astonished at how bad the sound had become. The line section tubes were also a bigger bottle tube marked AMPEREX, made in Poland, Anyone ever seen an Amperex made in Poland? Also wonderful sound. The Telefunken ECC88 is wonderful, but somewhat hyper/detailed and missing the ultimate vocal warmth of the old tube

Frap, the Tele ECC88 is a warm tube, I think you may have suffered a slow loss of resolution and bandwidth over the years, and are perhaps forgetting the sound of those original (supplied) tubes in your ARC. I agree that just before they departed this earth, they probably were very dark and in their own way, beautiful. An easy and inexpensive way to find if this sound is really what you want, is to buy some tubes at or near the lowest usable transconductance. A tube dealer would be selling you VERY used tubes and the price should be remarkably low. I suggest Telefunken, as the midrange is still beautiful, until it dies. I do agree with your comments about the Sovtek 6922, it sounds remarkably bad when compared to at least a dozen other possible candidates. You mention that the line section tubes "were" also bigger. Does that mean they were replaced at the same time? If so, you have two things going on at the same time that effect the SP10's tonal balance. Have you checked all the other tubes? If you are having to replace this many tubes in the output section, how about those in the power supply? If power supply tubes are bad, and you put in new 6922's, that would really provide a situation for poor sound.

Thank you Albertporter for confirming my suspicion that the"naturalness" was in fact due to tube wear. All other tubes in my unit were not replaced.Has anyone been able to replicate the great sound of these NOS tubes. We read how the Chinese and Soviets have "EQUALLED" the sound, but it may be a case just like the Stradiarious violin. What do you think?

The topic of tubes has been covered here many times, but to answer your question, the Russians have done a great job on some tube types and not well at all on others. Unfortunately, the tube you and I are discussing ( 6922 / 6DJ8 / 7308 ), has not seen quality manufacturing by anyone that can equal the best of the new old stock. There is a huge demand for this tube type, and the need grows every year. Perhaps a US importer or distributor will invest the money needed to get a break through in quality on this particular type. I suspect the Russians are currently building the best tube they can, given the budget, tools and materials they have to work with.

Any thoughts on tube selection (6922,6dj8, ecc88) for ARC SP9 mkII?