Velleman K4040 blowing new tubes


I have a problem with my Velleman K4040. The receiver has worked fine for several years with the original tubes that came with it from Velleman.
A couple of months ago I had to change my tubes, since one of the tubes was “dead” due to its lifetime.

I bought 8 new Svetlana C-Winged EL34, adjusted the bias with a volt-meter and everything looked very fine. But now the receiver is blowing the tubes - one after one. First the R101 resistor was blowned away, and I replaced the resistor and replaced the tube. Yesterday R102 was blown away and I have replaced this as well - with the tube.

Now I am just afraid that the next will be som other tube and resistor.
What is the reason for this? I have read several places that Velleman K4040 is blowing tubes, but why is this happening? The tubes are in good condition when I buy them (I test them in advance) so can you please guide me and give me some advice?

Thank you so much!