Pete, Aren't you glad you asked?...(:-> Jim w5ifp at gvtc.com On 4/3/2014 8:19 AM, Pete Smith N4ZR wrote: > I need to trouble-shoot my QSK system, which is built into my SB-220. > Will it do any harm to apply filament and plate voltages, but no > drive, to the 3-500Zs in the inverted position for a few minutes at a > time? >