Markus,
Have you discussed with George the option to change your cathode resistor from the stock 1K ohms to the recommended 1.2K ohms value. They are said to reduce the initial power surge (current) stress on the output tube. The Elrog engineers believe that this is issue with the Frankenstein amplifier. I've done this modification, only timewill tell if this is the answer.
Charles,
Have you discussed with George the option to change your cathode resistor from the stock 1K ohms to the recommended 1.2K ohms value. They are said to reduce the initial power surge (current) stress on the output tube. The Elrog engineers believe that this is issue with the Frankenstein amplifier. I've done this modification, only timewill tell if this is the answer.
Charles,