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Robust Driver stage recommendations
Robust Driver stage recommendations
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Old 31st January 2011, 10:39 PM   #1
alexmoose is offline alexmoose  United States
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Default Robust Driver stage recommendations

Hello DIY audio-ers,

I am looking for a driver stage to drive two KT-88s to AB2 in triode mode. Maybe even KT-120s if I feel the urge. I have all the expensive stuff purchased (Power transformer, OPTS, all that good stuff), and a pretty standard input stage, now all I need is a good PI and Driver. Any suggestions? I like Tubelab's octal driver circuit, but is the design sea worthy?

Any Help would be greatly appreciated, this amp will cook as soon as I get it up and running.

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Old 31st January 2011, 10:59 PM   #2
SpreadSpectrum is offline SpreadSpectrum  United States
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Use whatever voltage amplifier you want and drive with a mosfet source follower. If you do this right, you could even use a 12ax7 since the source follower gate is easy to drive.

A word of warning: do not full-power sine wave test KT88s in AB2 with mosfet drivers. You risk damage to the tube. Ask me how I know.
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Old 1st February 2011, 12:03 AM   #3
aardvarkash10 is offline aardvarkash10  New Zealand
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George's powerDrive setup has had what could only be described as "rigorous" testing...
"It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
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Old 1st February 2011, 01:30 AM   #4
Tubelab_com is online now Tubelab_com  United States
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I like Tubelab's octal driver circuit, but is the design sea worthy?
The octal driver circuit was designed in this thread in response to a question asked by member chrish that provoked my curiosity. It took 2 years and several diversions but Chris finished his amps and is happy with them. I built a breadboard and ran it through my usual abuse testing with good resuts. The breadboard still exists, and still works but I haven't made a complete amp yet. Yes I used it to crank 75 watts per channel out of EH KT88's in triode mode. I have also cranked several types of sweep tubes and other tubes with this driver circuit. The breadboard is saved for eventual comparison with another driver that I am currently developing.

6L6GC AB2 Amp

Pictures of Chris's beautiful amps can be found in post #111 here:


I have spent a lot of my rather limited spare time abusing and learning about Petes magic red board. This design won't do AB2 and is meant for sweep tubes. I am experimenting on another version of my driver circuit using pentodes in one stage and triodes in another with PowerDrive for AB2 operation. This is based on some of the things I am learning on Petes board. It will NOT be done any time soon. Petes board with minor modifications can make stupid amounts of power with cheap sweep tubes. My current version makes 125 WPC from $5 output tubes! I have seen 250 WPC from tubes that I got for $4 each.

Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 2nd February 2011, 08:00 PM   #5
alexmoose is offline alexmoose  United States
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Thanks a bunch guys, that circuit looks great. I'll let you all know how it works out
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