blaupunkt: F52UP (F 52 UP); Arioso

Dear tube radio friends Got a chassis of the Blaupunkt F62 UP Arioso. When the dial lamp and rectifier with its ellytics was replaced and the main switch repaired the set works very well. Even the magic eye (UM11) showing up bright and clear There's however a phenomena I'm wondering about, it's when turning on the set, I notice the dial lamp lighting up with a quite low brightness successively increasing to its normal light. The UL41 Telefunken (with a metal base) is the first tube in the heating chain. The chassis came with two spare UL41 tubes made also by Telefunken but without the metal base and when I tested these two I noticed that the dial lamp lit up with a very bright light successively decreasing until it reaches the normal brightness. The UL41 tubes are all made by Telefunken but yet you'll get a different function behaving of the tubes. Why is that? Is the UL41 with the metal base equipped with some kind of NTC or is it simply worn out and knocking on the tube heaven’s door? Best regards Lars-G.

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