Valve Tester

The picture shows my part complete valve tester which is based on a simplified version of the AVO model 163 with some ideas taken from the Sussex valve tester. The top section is complete and the lower section is under construction. The two sections will be connected via a multiway flexible cable and a D15 connector on the lower unit front panel.

I have added a simple facility to check Voltage Regulator tubes and Nixie tubes with a small selection of current limiting resistors.

The AVO selector switch or similar could not be procured so I have used a separate combination of rotary and toggle switches around the outer edge of the upper section to provide the equivalent functionality. The toggle switches cater for the heater connections (3A max) so the rotary switches only need to handle voltages up to 300V but relatively low currents (100mA max).

A D15 socket has been provided on the upper unit to connect to an assortment of external less common sockets or direct on to a valve via flexible cables and crocodile clips.

The main difficulties were in obtaining the multi-tap transformers to provide the heater and HT supplies. The solution was to obtain another, somewhat older, valve tester and use key components from that with some additions to fill in the gaps - a total of four mains transformers.

The picture on the right shows the lower chassis unit with the selector switches installed but less the mains transformers. A high current relay is used to switch the heater supply on and off, reducing the load on the rotary switches.

Quite a few of the 38 switch wafers on 9 switches have mostly wire links and just a few wires so the wiring process is not quite as difficult as it looks. All switches are break before make to avoid putting shorts on the mains transformers or rectified supplies.

The mains transformer wiring is complete and the transformers have been soak tested for several hours with no issues.

More to follow…..