[R-390] QSK; standby reduced fil. voltage; separate B+ on/off

[2002tii]

Sheldon wrote:

>Reduced filament voltage operation should be
>used for thoriated tungsten emitters only and does not
>apply to oxide cathode-type tubes.

And high-power transmitting tubes invariably use thoriated tungsten 
cathodes, while receiving tubes invariably use indirectly-heated 
oxide-coated cathodes (except for some rectifier tubes and some 
ancient triode types favored by certain audio loonies).  So 
procedures applicable to transmitting tubes may not apply to 
receiving tubes, particularly where the cathodes are concerned.

Best regards,

Don