The L7 I recently had instability problems and tune capacitor arc has been REPAIRED.? I managed with time and a jeweler file to clean the burn from the capacitor plate without removing it.? I gingerly tried the amp again and although it didn't arc the same spot it started in other spots on the tune capacitor.? Inspecting closely I found the tubes looked like Eimac but they were imports from RF Parts.? I changed those out for some OLD Eimac and very pleased to report PROBLEM SOLVED.? Everything behaved and tuning / loading adjust is now smooth as glass with NO instability.? It is as it should be on all bands!
Not to imply the RF Parts tubes are not good but the subtle differences between Eimac and those particular import ARE significant.? Now to find good tubes for the next time
Paul K0UYA
