[pubul57]

I've has my Atma-sphere for a while (don't yell at me, I also have the RM9SE) and was more than happy with the tubes that came with the unit - Chineese tubes but I don't know what manufacturer. So of course I called Roger and asked if he had any 6as7s. He was just buying a lage batch of these tubes, must be NOS from GE (they may be Russian made - don't know). Well Roger took a bit of time to get just the perfect matches, as is his way. The arrived a few weeks ago. First thing I noticed is they looked nothing like the Chineese and Russian variants I had seen before - much smaller. Put them in and Holy &(%!!!!. Everything improved, bass, mid range, highs, soundstaging, presence and detail. I have not idea if it is the fact that they are GEs or the fact actually takes the time to measure and match them. But the amps have never sounded so good. I don't know what Roger is actually does, but it seems that his tubes always have magic and worth the price.

[6BQ5]

I imagine he cherry-picks (and I say that in a good way).

[zybar]

Bet they would sound very good in my MA-1's, but to re-tube both amps would run almost $1000.00   

George

[pubul57]

I'm sure he does carefully select them ($35/each for that type of matching seems like a good deal) but these GEs also look very different.  I'm not sure how important the tube shape and size is, but they are quite different than the ones you get from Atma-sphere.

[Roger A. Modjeski]

The tubes are indeed GE, made in Owensboro Kentucky for the military (milspec). Indeed they are smaller but that's because the tube had become a GA (straight sided glass) rather than the older G (coke bottle). The Russians and Chinese never made that final step so their's are all G.

I had quite a time repairing/modifying and re-tubing a pair of early MA-1 amps for one of my customers a year ago. I bought enough tubes for both of his amps and some to spare. I had added cathode resistors (as per Atmasphere's recommendation)  which allowed me to check the current sharing of the tubes. With the resistors in place this is very easy to do and quite alarming. I put in unmatched tubes from the same lot and found that the sharing of current from one tube to the other was just horrible. I was not surprised as this tube was not designed to be biased from a fixed source. It's most common use was as a pass tube in a regulated power supply where the grid bias is controlled by the error amp and varies over a wide range as needed. This is also true of the 6C33 (triple nipple tube) which was designed to do the same. Therefore, I can't rightly blame the tubes.

The result of this study was that for a given negative bias voltage the tube currents varied more than 2 to 1. This presents a problem. I've spoken to Ralph Karsten about this and he doesn't mind the imbalance in tubes as long as one bank is close enough to the other bank be within the range of the DC balance control. However, tubes in a bank might not be sharing the work equally. It's like money, if each bank of tubes adds up to $100 that could be 5 $20 bills (5 equal tubes)  or a bunch of $1 bills making 5 stacks (tubes) that add up to 100 (e.g. 10, 20, 16, 14 and 40). That also adds up to $100. There's really no way of knowing unless you can determine the current of each tube individually. Further, the more off center you have to adjust the balance pot for 0 DC output, the more the banks are unequal as a whole. One bank may be biased at -60 and the other at -70 (or worse). That grid difference will raise even ordered distortion and cause the top or bottom of the wave to clip prematurely.The balance pot in the very early MA-1's I worked on had a very wide range.

Of course you can't determine any of this on a Hickok tube tester. I had to build a test fixture with very low drift regulated power supplies so that the measurements from one batch to another would be consistent. Plate voltage was held to better than 1% as was grid bias. I also tested them at the precise voltage and current that they would see in operation. There is no way to use double point (bias and gm) matching and get the accuracy required. BTW, I see lots of tube sellers claiming "double" and even "triple" point matching but they still aren't doing it right as several members have reported here. Ask them how double point matching works and why it is valid. I bet most of them don't know. Ask them if they measure Gm at a fixed grid bias or a fixed cathode current. So far all of them get that wrong too. They just jumped in on the research I did in 1982 when I started RAM Tubes.

As to George's cost concern; I can give guys with the big amps a break on matched set of 24. The small tubes don't require replacement nearly as often and don't cost much anyway. If you want to buy the small (driver) tubes at the same time let's call it $800 all together.

I have looked at pictures of several Atmasphere amps listed on Audiogon and could easily see the unequal tube wear. Just look at the tops of the tubes and note the size of the remaining gettering. When used at unequal currents for a long time the hotter tubes will have very little gettering left and the cool tubes may look like new.

Lastly, I have great respect for Ralph Karsten and his work. He has always been helpful with my questions about his amplifiers and he's a dedicated, no BS guy. That's rare in this industry.

[pubul57]

Roger, I don't how the word get's out on this sort of thing, and I am far from technically oriented, all I can say is that the difference in performance is so clear, that owning a pair of Atma-sphere amps without your tubes is a bit of a disservice to Ralph's great design - unfortunately they do need a lot of tubes, but really, your tubes are not that much more expensive than buying the Chineese stuff and if perfomance matters, and for folks who are willing to spend so much for the gear to begin with - it just seems like a no brainer. If w]I were Ralph, I would offer A RAM Labs Tube Upgrade Option with a little bit of a cut for him. I know he feels his amps cannot be truly appreciated with using his preamp; that may be true, but just as true is that using well matched and cherrypicked tubes is also part of optimizing the Atma-sphere amps.

[Roger A. Modjeski]

That's a good idea about the tubes. I'll also ask Ralph about why he so strongly recommends his preamp... other than the obvious. Thanks for pointing out that the price difference isn't so big. I was shocked to see how much they are charging for the Russian ones.

[pubul57]

When I last spoke with Ralph, I raised the issue of American made 6as7 and mentioned your GEs, he did not seem alarmed and actually commented that I would get even more power out of the amps, but I was not warned of problems to be concerned about. I have about 200-300 hours on the tubes and have not had any problems, I assume if there we problems they would have been made manifest by now, but I don't know that.

[Clio09]

Considering Ralph sells the Chinese tubes for about $25/tube these GE tubes look to be a good deal. I ordered 10 for my S-30 amp.

BTW - the RAM Labs Website shows on the Power Tubes page that these are GE tubes, but when you click on the link the description on the next page says they are Russian (6AS7 RU). The actual order form then shows they are GE again. Might want to correct that. It could be confusing to some.

[pubul57]

Another thing that would reduce confusion is to state the tube matching (pairs, quads, etc) charges up front, rather than just the single tube price without any matching fees; they should be disclosed before someone is ready to purchase. Matching fees, especially good matching is worth paying for, but they should be stated on the website.

[Clio09]

Well I got my tubes today and unfortunately there were issues. Upon a call to Ralph I learned that the 6AS7GA is not a compatible tube for the Atma-Sphere S-30 amp (not sure about the other models), they will short or blow when pushed. Luckily I wasn't playing music and had the amp on less the a few minutes.

So all prospective buyers should check with Ralph to see if your amp will accept the GA version.

[PaulFolbrecht]

Does anyone know if these tubes are still available?