Updating older hf amplifier
All of these amps, like the AL811H, push the 811 tubes pretty hard.
They are all rated at a kilowatt dc plate input on CW, as is the AL811H.
External airflow does not measurably improve anode cooling, and anode temperature is the limiting parameter.
See his link...airflow temperature measurements Absolutely true, if you consider operation in ICAS or CCS and not IVS (intermittent voice service).
This diode can be replaced with any 1 to 5 amp silicon power rectifier diode that physically fits.Gain is slightly higher on SSB or low duty cycle, because anode voltage is slightly higher.