Tubes Asylum Questions about tubes and gear that glows. FAQ

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Tubes Asylum ]

---

[ Alert Moderator ]

---

RE: McIntosh MC60 Bias Measurement

Posted by Michael Samra (D) on February 21, 2016 at 20:29:14

In Reply to: McIntosh MC60 Bias Measurement posted by rupertbear03@yahoo.com.hk on February 21, 2016 at 01:47:27:

Joe
On the Mc60s,you measure bias from pin 5 to ground of the 6550s.You should change out the bias rect to a silicon if it's original and you need to put an 8.2k or 10k depending on how the bias reads when you are done.
Keep in mind that Mcintosh uses a bias tracking system so at idle you want to have 430vdc on the plate at pin 3 and minus 45 on pin 5..You may have to use a variac to achieve this so no matter where you set the variac to get 430v st pin 3, you need to change a bias resistor to reach minus 45v..Then when you plug back in the wall,it will track where it is supposed to be.If it went up to 445v on pin 5,it will push the neg bias to minus 52 of thereabouts.That's because it is tracking properly.Put in the right bias resistor and you may have to experiment to get to the -45v if you changed out the selenium to a silicon.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

Edits: 02/21/16 02/22/16

This post is made possible by the generous support of people like you and our sponsors:

Analog Engineering Associates

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---