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

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tube DIY Asylum ]

---

[ Alert Moderator ]

---

Help with a Glowing Plate

Posted by darterboy (A) on August 10, 2006 at 19:43:06

Hi all-

Thanks for helping a noob! I recently brought home a Zenith stereo console amp from the junk store. It has 4x6BQ5 and 2x12AX7 and a 5U4GB rectifier. Brought it up slowly and checked for short circuits and bad filter caps with a Dim Bulb Tester, so far so good.

At full mains voltage, however, the plate on one 6BQ5 glows cherry red and no sound on that channel. I shut down quickly. Conventional wisdom (not mine, the archives') says bad coupling cap(s). I was gonna re-cap anyway.

So I replaced all the paper/wax and electrolytics (except the multi-section can) with new orange drops and electrolytics. When I powered up, Same problem. One tube still glows cherry red. The problem stays with the socket so I don't think it's a bad tube.

What to check next??

Could the un-replaced filtering caps in the PS be causing this?

If it helps, there are four test points on top of the chassis connected via resistors to the four output tube plates. There are also two pots- (bias adjustment?) one between the 6BQ5s of each channel- accesible from the top of the chassis.

Thanks for any help troubleshooting this problem.

-Stott

• The Dim-Bulb Tester (poor man's Variac)   (Open in New Window)

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

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

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

---