The CV7136 is at the cross roads between valve rectifiers and solid state silicon diodes. The housing and base is conventional looking, indeed the base is a standard IO, but inside are four silicon diodes. These can be used as required as each is brought out to separate pins.
A valve rectifier would be limited by the peak current and the input voltage would normally be given as an AC RMS voltage. The silicon diode is also limited by peak current but the voltage is given in terms of the Peak Inverse Voltage (PIV) this is because the reverse voltage, if too high, will cause a breakdown across the diode and lead to a complete short circuit. For a sine wave input the peak voltage is 1.4 times the RMS value. These rectifiers have a PIV of 400 Volts. This equates to an RMS input of 285 Volts. With a safety margin, silicon diodes die very fast if abused, this equates to a transformer voltage of 250 Volts.
The connections and conventional diode symbols.
The top of the envelope is domed - just like a valve. The envelope is black to radiate heat, but soon power diodes would be encapsulated so that their metal case could be bolted directly to the chassis or a suitable heatsink surface.
A standard International Octal base.
The wide metal tube envelope is 34 mm in diameter, and excluding the IO base pins is 31 mm tall.