jas@proteon.com (John A. Shriver) (12/28/90)
Well, I just got mail over the Christmas holiday from Stereo Cost Cutters. They claim that the 7199 tube used as the driver in the Stereo 70 has been discontinued. Not surprising, given the recent skyrocketing of the price to $23 each! There is no pin-compatible substitute for the 7199. This rather forces (eventually, I do have a good pair of 7199's) the issue of upgrading my Stereo 70 amplifier with new driver circuitry (not using 7199's!). SCC is offering a kit that retains the same basic topology, but using a 6GN8A tube. The design is Copyrighted by the well-known Frank Van Alstine. The 6GN8A is a triode/pentode designed for TV applications. This does not strike me as a path I would feel comfortable with. There are a lot of strange tubes out there that were designed just for televisions, and never used anywhere else. How long will it be before the market for this tube (6GN8A) dries up, and it too is discontinued? (Do you have a tube television that you would spend money to repair?) I would be much more comfortable using very common tubes, like the 12AX7 or 6DJ8. These saw use in a wide variety of fields, including instrumentation, so there will be a market for them. They may get expensive, but they will be made. Also, I have an empirical feeling that a triode design might sound better. Pentodes are not nearly as linear as a triodes, and modern designs use low feedback, and don't rely on it much. Thus, I am finally starting to consider the options for upgrades. Has anyone on this list built (or listened to) any of them? I am leaning towards the Curcio (Glass Audio 1/1) design, but am wary of the review in Glass Audio 2/1 that considered it "overly clinical". If I buy the Curcio upgrade as bare boads ($44 total), I suspect I can build it at a modest cost, but it is still a lot of time to do the work. I'd rather have some comments up front. (I have been happy with the Curcio preamp.) I know that GSI also has well-regarded upgrades. Are there any others that don't use 7199's? Is there a schematic for a dual-EL34 power amplifier in the "VTL Book"? (Of course, the day will come when the high-end audio market either gives up on tubes, or starts having them custom-built. This is not the first time a crucial tube has been discontinued. The Quicksilver mono's went through a design spin when a tube got discontinued.)