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I am taking about coupling capacitor between driver tube and the DHT. There are zillion way to do it and no one said that they need to be used. No one proved yet that a very good quality of caps shell be worse than other methods. In my case since the amp will be ultimately only HF it might use any coupling with equal success.

Since I might keep with 2A3 a very high grid resistor then I might use a very little cap. Furthermore if I want I might use the coupling cap as the high-path filter for my MF channel (it is 3200Hz electrical and 1000Hz acoustical). If so then the cap would be in nF level and it might be some kind of crazy expensive cupper in Teflon for instance… or even air. With 250K on 2A3 grid we arrive to 0.00018uf... what is 180pF – very much the capacitance that air cap can handle if they will be able to care the couponing voltage. I am a bit suspicion with this approach as in the past what I was wring the DSET curve with coupling capacitor in Mild I was not able to get my MF to sound right. I do not know what the reason was.

Alternately, since my driver stage has a very good RL filter in it’s grid and all the rest MF amps will run no bass I might use galvanic coupling. The problem with transformers is also bandwidth and phase distortion but in my care it might not be the factor (the beauty of DSET topology). Since my MF amp will not care LF the intestate transformer might have no inductance and to have as few tune as it need to do the coupling. I have ordered a very fast 1H transformer with 80% nickel core, 50ma gap, that shell theoretically run TV signal. OK, I am kidding about TV but it will have no phase problems under 100K. The transformer is made by a quite knowledgeable person, so it might be very interesting.

Probably I shell give a try to one of the direct-coupling versions. If I have higher voltage in super Milq then 400V then I might try the Jack Elliano’s idea of reactance coupling.

http://www.electra-print.com/2a3drd.php

Still, my leading at this point are air cap or a small and very none-inductive transformer that at HF shell be as good as a straight wire.

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