Type 86 400Hz Power Supply

The TF16 400Hz power supply in the T86 radar is now working!!!

As previously reported our member Pete M put in a lot of effort to develop a 400Hz power supply with the aim of running the radar simulator in the LCP. However, the large synchros proved to be too much of a load for Pete’s power supply. So Pete H thought he would have a go at resurrecting the T86’s 400Hz supply (location F16).

A note of caution, it is early days and the power supply hasn’t yet had a full load and soak test  but the attached images of meter readings show the F16 voltage and frequency output parameters.

F16 Output AC wm.jpg      F16 Output Hz wm.jpg

Whilst the T86 was in the care of the RAF Museum capacitors were removed by contractors who were tasked with removing any components in the T86  containing polychlorinated biphenyl (PCB) a toxic chlorine compound.  Not only did they remove those but  also all the electrolytic capacitors from the F rack power supplies!!

F16 Caps Removed wm.jpg

The loss of the electrolytic capacitors was no big deal as due to their age all would probably allneed replacing anyway. Several replacement capacitors are ‘near enough’ the same values of the originals, e.g. 10uf being used to replace 8uf which are not available at the correct working voltage. Here we are with the replacements fitted

F16 Caps Replaced wm.jpg

For the initial switching on of the 400Hz supply we connected it to a variable auto transformer (Variac) and wound it up gradually to 230V AC. The frequency and voltage of the output can be adjusted but after several minutes the voltage dropped by 15 V. Investigation showing that the 26V DC that is supposed to be across the output of the bridge rectifier was actually 33V. The mains input had to be wound down to 190V on the auto transformer to achieve the 26V DC and at that voltage everything became stable.

These two images show the wiring of the input transformer in the power supply  and its circuit diagram. The primary windings are giving too much voltage on the secondary so we shall experiment with the links to obtain the required voltage on load.

F16 Transformer Primary Wiring wm.jpg

F16 Transformer Taps wm.jpg

We have noticed that the power supply gives off a fairly loud 400Hz tone. Not sure if this is normal as in a working radar it wouldn’t have been noticed!


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