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Old 9th January 2012, 12:05 PM   #1
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Default High voltage driver for AB2 operation GU81m tubes

Dear All, out of another users's kindness and expertise (lem8r) a design was developed to push a gu81m, full pentode design, into AB2 operation.

the design is attached to this message.

Please feel free to comment....I m just a messenger so hopefully lem8r will jump in to reply to any observations:

Alex
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Old 9th January 2012, 03:11 PM   #2
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Seems like the long way around... using a KT88 to provide voltage drive to a Mosfet follower?? No power is required, only voltage swing from the tube driving the Mosfet.

I think I'd consider other means myself, and perhaps decide if a Mosfet is what I want or if I want to drive the output tube from another tube or not.

I'm not too sure about the bias means for the Mosfets either, but perhaps that will be sufficient...

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Old 9th January 2012, 03:34 PM   #3
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Well, pentodes are a good idea when you need lots of swing, but yeah, I'm with bear, KT88 is not an optimum choice. I'd scout through some databooks and find a HV pentode with a more reasonable power rating (a few watts, not 35!), then start experimenting. There are some interesting linearization tricks you can do with the pentodes in a differential configuration.
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Old 9th January 2012, 03:46 PM   #4
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thankyou to both of you for the inputs.

Unfortunately custom transformers must be made to suit specific design requirements. The idea is to have a working design to fabricate transformers....with a working basis experimentation can begin...

I personally do not have enough spare material to simulate this design on a breadboard

What would greatly help would be to have a working design with very good or good chances of working adequately.. Modifications would go from there to an optimized design.
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Old 9th January 2012, 03:59 PM   #5
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Have you seen this? Apparently it's a working prototype.

Class A2 Direct MOSFET Coupled SE
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Old 9th January 2012, 04:15 PM   #6
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AB2 on a GU81m? Are you nuts? A pair in full class A is still going to deliver 400W, give or take all without swinging the grid positive. You have an OPT good for 400W? AB2 ought to be capable of nearly 1kW output. Back to the 'Nuts?' question...
cheers,
Douglas
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Old 9th January 2012, 04:18 PM   #7
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OT, hey Douglas, can I ask you privately a few questions about your 4E27 amp? I'm planning to build something around the few 4E27 tubes I got.
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Old 9th January 2012, 04:21 PM   #8
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A custom transformer can be made for this application.
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Old 9th January 2012, 05:00 PM   #9
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Quote:
Originally Posted by Alexontherocks View Post
A custom transformer can be made for this application.
I don't believe it. Biggest I have seen is for the Altec 260. 813 amp, power output under 300W and I will bet against going any bigger w/o significant issues. Go ahead though, I'd love to see how you do it.
cheers,
Douglas
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Old 9th January 2012, 05:05 PM   #10
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will be happy to surprise you..
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