|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
|
|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
In Reply to: A Question on Tube Longevity. posted by Grant99 on September 24, 2000 at 16:28:11:
In my experience, aging in class A small signal stages is determined by the static bias/load conditions the tube is operated in, and not by the excitation. Therefore the tubes will age no matter whether they are run idle or amplify signal.If you are running tubes close or beyond manufacturer's maximum ratings, they may age more quickly. Rough cold starts may have a negative influence on the tube's life, too, so soft start is recommended.
Another failure mode that is often overlooked is 'cathode poisoning' in underheated or current-starved stages - the cathode may build up a resistive/non-emissive layer over time if left heated without current, driving up noise figure and Ri, reducing gm - sometimes tubes will fail completely. Cathode poisoning was a very troubling problem in the days of TV Tuner front-ends - especially for UHF.
Some Special Quality tubes have specially treated cathodes which are immune to that failure mode, but many common small signal and power tubes do not, so it is not a good idea to try to preserve tube lifetime by running them heated with anode voltage supply interrupted.
So you will have to live with the ageing of your phono preamp tubes, or modify your amp to switch off the phono stage completely when not used...
Regards,
---mb---
========
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: A Question on Tube Longevity. - mb-de 03:36:05 09/25/00 (2)
- How do I attain a "Soft Start"? - Grant99 18:45:16 09/25/00 (1)
- Re: How do I attain a "Soft Start"? - Adrian 22:42:24 09/25/00 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
