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hacknet 23rd August 2004 12:25 PM

Drd Kt88?
is it possible to DRD a KT88 with operating points around 350 B+ and 100ma current draw, on 3k irons?

Thanks A million!

smbrown 24th August 2004 05:19 PM

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.

smbrown 24th August 2004 08:39 PM

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!

hacknet 25th August 2004 06:59 AM

hmm... the way it looks, i might just drop the idea of a DRD.

are there any reputable KT88/5881 SE amps that i can use as reference material?

jogas 25th August 2004 07:36 AM

have a look at this site

hacknet 25th August 2004 11:10 AM

thanks for the links. i`ve seen them before and decided against them because i don`t quite like the EL34.

any others?

smbrown 25th August 2004 09:15 PM

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.

hacknet 26th August 2004 06:14 AM

hm.. thats true... could you share you schematics?

jogas 26th August 2004 08:56 AM

have a look on this site, there are a lot of schematics

hacknet 26th August 2004 09:10 AM

many thanks!

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