What are the differences between DRD and Loftin White?

[Fai C]

Hello!
I saw this circuit that is Loftin White:

http://www.audiodesignguide.com/Fiat/GM70d.html

And this is DRD:

http://www.enjoythemusic.com/magazine/equipment/0206/welborne_laboratories_300b.htm

Regardless the tube type they both using, both are direct coupled from
the driver stage to output sections. Are there any difference?

I'm really curious. Some says the Loftin White is very hard and
dangerous to deal with compare to DRD, is it?

Happy holidays!!

[Alex Pogossov]

"Fai C" > wrote in message
...
> Hello!
> I saw this circuit that is Loftin White:
>
> http://www.audiodesignguide.com/Fiat/GM70d.html
>
> And this is DRD:
>
> http://www.enjoythemusic.com/magazine/equipment/0206/welborne_laboratories_300b.htm
>
> Regardless the tube type they both using, both are direct coupled from
> the driver stage to output sections. Are there any difference?

Alex:
It appears that the first circuit uses three fixed supply voltages, the
second one uses voltage drop on the output stage cathode resistors as supply
voltage for the driver. The second circuit is simpler, but far less
efficiens as rather considerable power will be dissipated in these
resistors.

[John Byrns]

In article >,
Fai C > wrote:

> Hello!
> I saw this circuit that is Loftin White:
>
> http://www.audiodesignguide.com/Fiat/GM70d.html
>
> And this is DRD:
>
> http://www.enjoythemusic.com/magazine/equipment/0206/welborne_laboratories_300
> b.htm
>
> Regardless the tube type they both using, both are direct coupled from
> the driver stage to output sections. Are there any difference?
>
> I'm really curious. Some says the Loftin White is very hard and
> dangerous to deal with compare to DRD, is it?

I wouldn't call the first circuit a ³Loftin White², I reserve that name for the
original circuit which used a single power supply and a screen grid input tube,
but that's just me. Although both amplifiers are spin offs of the Loftin White
circuit, if anything the second circuit, which you call the ³DRD², looks closer
to the original Loftin White.

The main difference that I see between the two circuits, excepting the different
types of input stage, is that the second circuit uses cathode resistor bias for
the output tube, while the first circuit uses fixed bias for the output tube.

It's not obvious to me why the first circuit should be harder and more dangerous
to deal with than the second, given that everything else is equal, i.e. the same
output tube and plate supply voltage.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

On Dec 26 2011, 5:33*am, John Byrns > wrote:
> In article >,
> *Fai C > wrote:
>
> > Hello!
> > I saw this circuit that is Loftin White:
>
> >http://www.audiodesignguide.com/Fiat/GM70d.html
>
> > And this is DRD:
>
> >http://www.enjoythemusic.com/magazine/equipment/0206/welborne_laborat...
> > b.htm
>
> > Regardless the tube type they both using, both are direct coupled from
> > the driver stage to output sections. Are there any difference?
>
> > I'm really curious. Some says the Loftin White is very hard and
> > dangerous to deal with compare to DRD, is it?
>
> I wouldn't call the first circuit a ³Loftin White², I reserve that name for the
> original circuit which used a single power supply and a screen grid input tube,
> but that's just me. *Although both amplifiers are spin offs of the Loftin White
> circuit, if anything the second circuit, which you call the ³DRD², looks closer
> to the original Loftin White.
>
> The main difference that I see between the two circuits, excepting the different
> types of input stage, is that the second circuit uses cathode resistor bias for
> the output tube, while the first circuit uses fixed bias for the output tube.
>
> It's not obvious to me why the first circuit should be harder and more dangerous
> to deal with than the second, given that everything else is equal, i.e. the same
> output tube and plate supply voltage.
>
> --
> Regards,
>
> John Byrns

There is no end to some folks determination to produce direct coupled
amps without capacitor couplings, thus needing rather high voltages in
PSUs.
I find it interesting, but I see no need to get rid of capacitors.
Good caps are made these days, unlike when the Loftin White was made
in the 1930s and when caps were rather dodgy technology because it was
before the time of decent plastic films and sealants etc. Coils and
transformers seemed to be far more reliable than either resistors or
capacitors.

In the amp O made with a pair of 845 in parallel SET, I used TWO main
voltage rails, +600Vdc and -600Vdc, to deliberately avoid the
existance of high voltage potential between anode OPT windings and
earthy OPT secs and other nearby metal parts. I kinda went in the
opposite direction to those who don't mind high voltages.

Patrick Turner.