The amp was shoe-horned into an existing gravitometer box,
complete with meter. The modulator and HV supply, (not shown), are separate.
The 813 is fed with about 15 watts of RF from the TR-7. The 811's are
fed from a RS 25 watt amp, through a backwards connected audio output transformer.
The 813 can work 40, 75 and 160 meters. Pull the yellow 'rod' to get additonal
plate tune capacitance on 160.