The Brandenburg Alpha Series II 5 kV Power Supply is from Great Britain and made in 1977. The model 2507r is specified for 500 to 5000 VDC at 5 mA, around 100 VA power rating.
I bought this Brandenburg Alpha Series II 5kV high voltage power supply from a University in France, cleaning out. I was lucky to spot this HV power supply among many pictures put up in a Facebook group called Vintage Electronic Test Equipment: https://www.facebook.com/groups/VintageElectronicTestEquipment.
I have many different power supplies, both mains and high voltage. An overview of my own power supply projects can be found here: https://kaizerpowerelectronics.dk/general-electronics/.
Inside the Brandenburg Alpha Series II 5 kV power supply
The front panel controls consists of a analog high voltage meter. Coarse and fine dials for adjustment of the high voltage. Mains switch and fuses. Polarity indication and reset of tripped over-current. The rear panel has input for a remote trigger and the polarity of the high voltage can be changed from turning a module 180 degrees.
The mains input goes through an isolation transformer down to around 40-50 VDC. 2N3055 (at the back) and BDY91 transistors (with heat sinks inside) seems to make up the inverter to drive the high voltage flyback style transformer. The manual states that the drive frequency is around 33 kHz. The output of the flyback transformer goes to a large grey module, which is assumed to contain some kind of rectification and possible voltage multiplier. The manual shows that this is a 10 stage CW multiplier, made from BY182 diodes and 2 nF capacitors.
The two controls PCBs are marked PC1 and PC2. PC1 is the amplifier and reference voltage supply. PC2 is the trip protection board.
The output was tested with a Fluke 77 that can measure up to 1 kV.