The 4CX800/GU74B is used in the Alpha 91b, 99, and 8100 amplifiers. These are russian tubes that have been tested in an actual Alpha amplifier and are guaranteed for 1 year from date of purchase.
Note: The 4CX800 (gu74b) tubes used in the Alpha 99 and Alpha 91ß are freely available on the Internet, however, most often not as a matched set and not with a warranty. Purchasing non-warranted (i.e. non-tested) tubes from anywhere and putting them in your amplifier exposes you to a risk of catastrophic failure – we’ve seen it happen to customers and it happens to us occasionally as part of our testing and warranty procedure for tubes
