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.
Recommended for: HH Scott 222C, McIntosh MR67, VOX, Dynaco, ...
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!!!
See also my other auctions and visit my eBay store for more vintage tubes and tube parts. More than 250000 tubes in stock and more than 35 years in tube business.