UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Adding a selectable line input to valve radiogram

Rich400 · 29th Oct 2020, 4:05 pm

Re: chassis isolation transformer sizing

the two items to draw load on this gram are the chassis and the deck of course.

I would guess 15w for the deck so that would leave 135w for the rest (Chassis).
So deducting the heater load as its covered by the T3 autotransformer would leave the loading I have to cover to perform this mod to remove the live from the chassis.

The trouble is I have researched the valve loads and I'm not confidant my calculations are reliable, so unless anyone else has a better suggestion I will size my new isolation transformer at 135w (or the closest i can find) which will give me the headroom of the load that is being performed by the heater autotransformer.

I would like the smallest physical dimensions to enable a neat fit for the mod.

I am not sure if there are preferred suppliers regarding cost/quality, but recommendations are again welcomed.

29th Oct 2020, 4:05 pm	#69
Rich400 Tetrode Join Date: Oct 2020 Location: Lowestoft, Suffolk, UK. Posts: 71	Re: Adding a selectable line input to valve radiogram Re: chassis isolation transformer sizing the two items to draw load on this gram are the chassis and the deck of course. I would guess 15w for the deck so that would leave 135w for the rest (Chassis). So deducting the heater load as its covered by the T3 autotransformer would leave the loading I have to cover to perform this mod to remove the live from the chassis. The trouble is I have researched the valve loads and I'm not confidant my calculations are reliable, so unless anyone else has a better suggestion I will size my new isolation transformer at 135w (or the closest i can find) which will give me the headroom of the load that is being performed by the heater autotransformer. I would like the smallest physical dimensions to enable a neat fit for the mod. I am not sure if there are preferred suppliers regarding cost/quality, but recommendations are again welcomed.