Pictures of the internals of the 819 line GM2891-13.
Nine ECL80 triode-pentodes are employed in this instrument.
Modulator employs an EC80, a high slope UHF triode. Four grid pins so it was designed for grounded grid operation. Wil check this later today.
https://www.radiomuseum.org/tubes/tube_ec80.html
DFWB.