 |
 |
|
|
|
These sets were designed to work with an HT battery,a grid bias battery and a "wet" accumulator. In general these are not available today, quite apart from being not particularly desirable. Suitable transformers are not readily available to make a power supply either, though there are probably specialists on the web who can help. The remedy often adopted is to rewind the secondaries of an existing mains transformer; but this is a task that not everyone wishes to tackle.
It has been suggested that a solution is to use two separate "off the shelf" transformers , one for HT and one for LT,. It is additionally possible to obtain a grid bias supply from either of these.The power required is not great and 3VA midget printed circuit board transformers offer a compact solution.
 |
The power pack above was produced to drive a 1926 Graves "Vulcan" (2 valves) A still-available 4.5 volt flashlamp battery is used for grid bias in this particular set, but the components within the dotted line may be added for sets which require a GB supply from the power unit.
The circuit diagram above shows separate HT and LT portions, but better stabilisation can be obtained by cross linking the two circuits. This modification is shown in RED on the diagram below.
