POWER TRANSFORMER FOR 13E1 POWER AMP

The power transformer needs to supply 430V DC to the power tube anodes, and also voltages to the input circuits, EL84 driver circuits, and the 250V regulator for the power tube screens. So, the transformer secondary needs to be about 340V AC. The total current delivered will be a little less than .35A per channel. Also it needs to supply 26V AC to the 13E1 filaments and 6.3V to the 6SN7 and EL84 filaments. The input data to my spreadsheet is shown below.

I am using a bobbin with a center-leg-width of 38.1mm and a stack height of 50.8mm. The calculations give a TPV (turns-per-volt) of 1.96, which is pretty high, and will mean more wire, but it will allow the transformer to run at a lower flux density and avoid saturation of the core and rattling and buzzing and other irritating stuff. Hopefully.

With the wire sizes shown, and the number of layers required for each secondary, the spreadsheet results below show that I should be able to fit all the secondary windings on with a few mm to spare. Efficiency calculates out to 96%, and predicted temperature rise is only 13 degrees celsius.

Time to start winding. The bobbin is on the winder, and the 18ga wire is ready to go. The right image shows the first layer carefully wound onto the bobbin.

The remaining layers were applied with a few millimeters to spare. Below are the 2 finished power transformers, with the bells attached, so you can't see the bobbin, but you can see the dirty appearing laminations vacuum impregnated with varnish, so the transformer absolutely does not hum! The transformer on the right has bridge rectifiers attached to it.