[Amps] Drake L-7 arcing on 80m

[Bill Dzurilla]

Hello,

I recently acquired an L-7 amp and I tried it out
yesterday.  I used my Pro II as the exciter, an amp
keyer, and a dummy load.

There seems to be some problem on 80, unfortunately. 
On all bands, I started with 20 watts drive and slowly
increased the drive while tuning for max output.  When
I got up to about 600 watts out on 80, I heard and saw
through the meter a blue arc.  This happened twice on
80, and I did not want to try it again.  No arcing at all on 40, 20, 15, or 10.

I opened up the amp and everything looks OK, except for one of the 25 or so stators on the plate tuning capacitor has graffiti-like white traces on it.  I suspect this is the source of the 80m arcing, as the rotor does not go over the spot with the traces when set to 40m and up.  I have not tried the amp on 160m, but if my theory is correct it would arc on 160 as well as 80.

The capacitor plates are not dented or deformed in any way.  Have not tried the amp on the WARC bands.

So, do you think the stator is the source of the problem?  If yes, is there any fix?

73, Bill NZ5N