The GATES BC-250T uses the 810 tube type, two in the RF and two in the Modulator. The rectifiers shown are 866 and 8008 mercury vapor. The BC-250T could be field converted to a BC-1T that involved converting tube types to 833A. The manual  for the BC-250T or the BC-1T is available for purchase on this site. Note also that I have the field upgrade literature.
GATES RADIO COMPANY
BC-250T TRANSMITTER

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