Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Use this form to submit comments directly to the Asylum moderators for this forum. We're particularly interested in truly outstanding posts that might be added to our FAQs.
You may also use this form to provide feedback or to call attention to messages that may be in violation of our content rules.

You must login to use this feature.

Inmate Login

By default, logging in will set a session cookie that disappears when you close your browser. Clicking on the 'Remember my Moniker & Password' below will cause a permanent 'Login Cookie' to be set.

Moniker/Username: The Name that you picked or by default, your email. Forgot Moniker?	Examples "Rapper", "Bob W", "joe@aol.com".
Password:	Forgot Password?
	Remember my Moniker & Password ( What's this?)

If you don't have an Asylum Account, you can create one by clicking Here.

Our privacy policy can be reviewed by clicking Here.

Inmate Comments

From:
Your Email:
Subject:

Message Comments

Original Message

RE: You're welcome

Posted by Triode_Kingdom on August 10, 2017 at 13:53:09:
"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...