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#1
Posted to rec.audio.tubes
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What are the differences between DRD and Loftin White?
Hello!
I saw this circuit that is Loftin White: http://www.audiodesignguide.com/Fiat/GM70d.html And this is DRD: http://www.enjoythemusic.com/magazin...ories_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!! |
#2
Posted to rec.audio.tubes
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What are the differences between DRD and Loftin White?
"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/magazin...ories_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. |
#3
Posted to rec.audio.tubes
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What are the differences between DRD and Loftin White?
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/magazin...boratories_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/ |
#4
Posted to rec.audio.tubes
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What are the differences between DRD and Loftin White?
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/magazin...lborne_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. |
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