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RE: You're welcome

"Its a big deal getting rid of that output coupling cap!"

We're definitely on the same page on that point. I'm expecting this to provide an output Z of a few hundred ohms, and there won't be any phase shift or coloration from a large series cap.

About the opamp, I already have a few OPA445s on hand for this project. This device is rated to +/-45V, and that's what I need to handle the bias voltage directly. The followers will be 5686s in pseudo-triode. With this tube, the DCR of the cathode choke (~2,200 ohms) dictates a negative supply of roughly 24-28V at the bottom of the choke. With the cathode at zero, that will produce about ~12mA current into the cathode. To keep the cathode at zero, I'll need about -18V to -20V on the grid. So, I believe the simplest plan will be a +/-28V supply using a LM317/LM337 pair. That will provide the negative voltage for the tube, as well as powering all the active components and the output relays. Now, if I can just find time to start on the chassis...




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Buy Chinese. Bury freedom.


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  • RE: You're welcome - Triode_Kingdom 13:53:09 08/10/17 (0)

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