[Mondial]

It is not surprising that the 300 ohm resistor gets hot. It replaces the field coil of the original speaker. If you look at the original schematic, there was a voltage drop of 75 V across the coil. If you consider the same drop across the 300 ohm resistor, it dissipates over 18 watts under normal operation. This is only an approximation because the actual voltage across the resistor is a rectified sine wave vs. pure DC, but it does give some idea of why the resistor gets so hot.

I would use two 600 ohm 20 Watt resistors in parallel, or use a 300 ohm 50 watt chassis mount heat sinked resistor that looks like this:

You can buy a 300 ohm 50 W like that from Mouser.
http://www.mouser.com/ProductDetail/Vish...0fVJ72M%3d

[Image: http://www.angela.com/images/products/detail/rcd.jpg]