Grampian ENSA UA

[Lucien Nunes]

Due to the lower cost and size, many 230-110 transformers for general use are auto because it is assumed that the appliance will provide the necessary isolation and the transformer is only there to change the voltage. Hopefully the 150VA transformer will have enough headroom to allow for the halfwave rectification. Only the HT current will appear as DC in the secondary but on a small commercial transformer even a modest amount of DC load can push it into saturation.

I think it's nicer to retain the dropper resistance and avoid the 110V stage. It helps to avoid warm-up surge that can occur when a series string is not ballasted by a fixed resistance, as some valves can warm up more quickly and see a greater fraction of the voltage until the others catch up and increase to their hot resistance. The more resistive ballast in circuit, the more it looks like a current source.

One has to decide what to do with the chassis; if there is no risk of the isolating transformer being bypassed, it would be nice to earth it, which would result in the neutral being connected to the chassis. If mains could be applied without the transformer, that would not be acceptable and it would be best to fit a new isolating capacitor as original.

[Doris The Diode]

Update,

I bought an isolation transformer and connected earth to the secondary winding which goes to the old nuetral and it works, it does not trip the fuse anymore!

Thank you for everyones help

Now to find a box for it.

DD