They can be used in modified Dynaco ST-70 PC-3 board which accepts 6GH8A instead of scarce 7199. They also can be used in original Dynaco ST70 driver board using special noval adapters.
We have few more than 50 pcs of these tubes and all pairs we have are carefully tested and matched by plate current on calibrated Metrix U61-B tester. Due to big number of tubes, they are perfectly matched within 5% or less!!!
Brand: TELEFUNKEN
Type: ECF82
Model: ECF82 6GH8A
Country/Region of Manufacture: Germany