• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Drd Kt88?

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#2
Well, you'd have to find an output transformer that you're comfortable running at 100ma, single ended - not such a small task. I have some AN 2.6k that are rated for 180ma (two 845's), and they sound nice but weigh a ton!

Otherwise the DRD design should work fine as you've outlined. Much will depend on a driver that can swing the voltage required and offer a fairly low impedance. If you look at the design on Jack Eliano (sp?) website (electrapint) you'll see the driver is done in parallel to lower the Rp. When I built a DRD EL34 amp the lower I got the driver impedance the better it sounded. That means bypassing the cathod R on the driver, too.
 
#3
Almost forgot to add that, of course, you'll have to have a pretty high HV supply - maybe on the order of 550 to 600 volts? I will also say that when I built mine I used all Electraprint iron, and even so I found the sound to be a bit dark. I finally converted it to a regular SE amp - using EL34 in triode mode. Sounds better to me, but YMMV.
Best of luck!
 
#7
Don't be too hasty to abandon the DRD. I think there is lots of potential in any design that has no caps in the signal path (well, I guess the one from the OPT to the cathode of the output tube is one). It may be that I din't have the patience to tweek operating points fully. And if you've done the DRD you can always convert it to a more conventional SE by cap coupling, changing the output cathode resistor and you can still use the choke to load the driver stage.
 
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