[Arran]

The 41-280 uses a power output circuit called "Screen Grid Inversion", the 40-290 just uses a more conventional tube based push pull power output with a phase inverter. The screen grid inversion circuit actually works quite well, but the power output is not as high and the distortion level is higher then a proper push-pull circuit, but less then a single ended output. It did everything that it was supposed to do, the 41-280 and it's 1940 and 42 siblings were extremely popular, and they used the same chassis and circuit in a series of table sets too.
Regards
Arran