[Amps] FL2100Z VHF surpressors failure

[Thomas Hoeppe]

Hello amp specialists,

at my home QTH I am using a small Yaesu FL2100Z amplifier since some months. I like this quiet little box, as 500W is the maximum I can run here at home. All my home made amps caused too much troubles here.  Since some days I am QRV again on 20/15/10. Unfortunatelly the beam has bad SWR in the CW segment of the 20m band. Today I tried to break a pile-up running 500W at SWR 1:4. Yes, I know I am guilty! But I am still used to my homebrew stuff where such things never caused troubles. The best matchbox was the built in Pi-filter, hi. 
Suddenly I got full current without drive, and there were arcings in the VHF traps. The arcs occur from the small coil to the 33 Ohm resistors, again without drive. It is amazing.....is it possible that these lazy tubes oscillate on higher frequencies? The gain is low, and the maximum frequency of this old bulbes is low, too. Both VHF traps show several traces of arcings, and both resistors have holes in the ceramic. Sometimes I saw the idling current again, and the next RX/TX switch over showed full current again. I got the linear with the advice that the tubes are damaged, but I am on the air with them since one year. If the tubes were damaged, there would be just DC current, but arcs in the surpressors show the presence of HF in the higher frequencies.

Anyone has experience with those kind of linears?

Tom, DJ5RE

PS: I also wondered about the DC blocking C: 1000nF only, although this linear is made for 160, too. The diagramm shows 5000 pF.....hmm!