jas@proteon.com (John A. Shriver) (03/07/91)
If you want to maintain a Stereo 70 with the same circuit topology, you have to replace the driver board, due to the unavailability of the 7199 tube. But that's OK, because the capacitors on the existing driver board are almost certainly leaky, and the resistors drifted. While I haven't tried it, I think that Triode Electronics of Chicago has the best idea of how to replace the 7199. Their driver board repalces the two 7199's with two EF86 pentodes, and one 12AX7 dual triode. Otherwise, the circuit is pure Dyna. These tubes are still readily available, even in very good versions. They are designed for low noise. They are the classic tubes used in the orignal Mullard EL34 amp design. (They also plan to offer a version with the Mullard topology.) I have had no problems whatsoever with Triode. Sound Values (nice folks, I like them too) chose to use 6GN8A's selected for low noise. Selected tubes is a big hassle, and how long before the 6GN8A is discontinued? That's a TV tube, there aren't many people trying to keep tube TVs running anymore. On the other hand, their design does have the advantages of Van Alstine's tweaks, which are sensible. The input bandwidth filter is a very good idea, and is an old idea.