Conclusion regarding the National NCL-2000 band switch:
The band switch that was used in the NCL-2000 is the same OAK switch configuration as the Beta switch that Hallicrafters used in the pre-release SR-2000. It failed almost immediately when using the 20 or 40 Metre bands. Arcing could be provoked by increasing the line voltage to 122 or 244 volts and very lightly loading the finals (35 ma) of screen current in high power mode.
The changes that were made to the SR-2000 switch can be replicated to the NCL-2000 switch to eliminate the arcing risk on 40 metres and significantly reduce the risk on the 20 Metre band by more than 50%. There are newly manufactured switches available for the NCL-2000 but they are simply the same old switch configuration and further, they use silver plated copper. The original switch used coin silver or spring hard sterling silver not silver plated components. Doesn't make sense to install a switch that is certain to fail again.
The notion that the switch in the NCL-2000 is mainly attributable to operator error is ludicrous. Also ludicrous is the notion that the 10 pf capacitor used on the rear wafer between the 20 and 40 Metre contacts is somehow responsible for the arcing problem in the front switch. Had they used a shorting band switch like most designers, the problem with unintended resonant conditions in the unused coil section would not exist. You won't find this capacitor in the SR-2000 because it used a shorting switch in the rear wafer.
The shorting rear switch leaves the unused inductor segment so fractured that it can only resonate at well over 150 Mc. Too many octaves for any disturbances. The UNSHORTED band switch leaves a much larger coil segment that will be resonant at very close to the second harmonic of the fundamental frequency on at least one of the higher bands. What does this do? The transmitter does not pass harmonic muster. Does it cause the peak voltage in the tank to increase? NO, it reduces the Q of the coil slightly. The 10pf capacitor on the rear wafer is not responsible for the front wafer failing.
If you do nothing else, install the jumper or 50pf capacitor between the 40 and 80 Metre contacts on the front wafer. This will eliminate the risk of arcing on 40 Metres. If you use the 20 Metre band, configure the front rotor plate as per the B level switch update. It doubles the gap on the front switch. Do not use the 1971 update because it has not been regression tested using AM mode. The B level update is fool proof to install.
ADDED NOTE: Please review the New band switch configuration for SR-2000 and NCL-2000 service note for a fix for the front wafer on the SR-2000 and NCL-2000. The photo's are of the NCL-2000 switch integrating double gaps for both 80 and 40 Metres. The SR-2000 requires only three contacts; the 80 and 40 meter contacts are jumpered together not requiring the additional 80 Metre contacts.
Hope you found this interesting and helpful. Thanks for taking the time to review this material.
Kindest regards Jim K9AXN 10/07/2014