In praise of ... Loftin White

A couple articles below into LW history.

http://www.studiomaudio.info/loftinwhite.html

http://www.audioasylum.com/cgi/m.mpl...t=loftin+white

[Richard]

Originally Posted by prince of darkness

My take on the Loftin White is that the special feature is the direct coupling between the driver and output stages.
The apparently high H.T. is used to eliminate the capacitor that would otherwise be used to block the D.C. The D.C. element of the drivers output is counteracted by raising the entire output valve by approximately the same voltage. So if the output of the driver were to have a 50V D.C. content, the heater would float around 50v (if A.C.) and the H.T. would be 50V higher than a conventional design.

I don't know about what makes a LW but this feature was also used many years later by Mullard for the first stages of the 5-20. More elegant than the Williamson for example. That said, the Williamson first stage is direct coupled and the higher cathode voltage is just a result of this.

Rich

[Dave the bass]

Thanks for the pointers Will.

David and Phil, my plan is soooo cunning that the cun-detector on my pootar has cut-in and wont let me type it but I can tell you that %£%^ * *&) ^ ( (% with a great big %^ %$%& *(__))_ _*&&^^ % %££&*__(&7 % ^&%$ %&*.

Bah, look at that, the cunning detector has blotted out some of the words again

DTB

[acorn]

The Mullard SE, 3 watt valve amp using the EF86 and EL84 is DC coupled, is this not in a similar vain or am I missing something here ?.
Acorn

[prince of darkness]

I think there may be a lot of different ideas about what constitutes a Loftin White. Not all the circuits I've seen use a pentode driver. All have used a directly heated triode for the output valve. Whether a pentode or beam tetrode output stage would be accepted as a loftin White, I have no idea.
Also I note that in the Mullard circuit, the stages are coupled through a resistor, whereas the Loftin White connects the driver straight to the output valve.