Home  |  Audio Reviews  Audiophile Shows Partner Mags  News     



Enjoy the Music.com Review Magazine

Sound Practices Magazine Online!

Sound Practices Magazine Online!

The Rejuvenation Process

How to get the longest life out of your power triodes.
Article By Heiner Jakobi
From Sound Practices Issue 8, Winter 1994/1995


Sound Practices Issue 8, Winter 1994/1995  Since there is a shortage of high quality power triodes just like in the 1940s although, touch wood, for different reasons -- it is necessary for the tube amp user to consider some old recipes which were common in the 1940s and earlier on. This one was passed on to me by an old tube lover from Germany.

I will use as an example the European type AD-1. This tube is considered by some to be one of the best output triodes ever built and it has become very rare.

The AD-1 was invented by Philips in Holland and built there under Philips and Valvo and by Tungsram and Telefunken in Germany. Later, Tesla made a copy which was not on par with the Western European production. A professional version with different basing called the Ed was produced by Valvo under contract for Siemens for use in telecommunication systems. Also, RFT from East Germany built a tubular version, later replaced by the even more powerful, indirectly heated Ec.

A regenerated tube does not look like a new tube. The shiny getter deposit will still look "burnt" or "bleached" like it was - but the tube will perform for its full life one more time, usually another 2000 hours. If regenerated yet another time, it might last another

AD-1 data
Filament 4V/0.95A
Plate voltage 250V/60 rnA
Negative grid voltage - 45V
That's all you need to know!

We start with the heating process: Instead of 4 volts we use about 7 volts and overheat our triode for about 10 minutes! Then go down to 5 volts on the filament and add plate voltage. Apply so much that the plate starts to glow red. That's right! Most important is a milliampere meter to read how much current the triode is drawing. With an AD-l, the max current is around 250 mA and this occurs around 600 V on the plate.

When new tubes are produced, a small amount of barium compound is vaporized inside the sealed tube in order to bind gases and impurities inside the glass. What we are doing is using getter material that wasn't used during the initial production process. Up to 60% of the barium is left over from the first process and we can use this potential now to rejuvenate the tube! As you heat the tube, you will see the barium glowing green, evaporating, and doing its proper job all over again.

The critical thing in this process is that you keep your eyes on the meter. After about ten minutes (and this time will vary), the current drops. You must switch off IMMEDIATELY!!! One second too late and the tube is dead! Forever. You have not lost anything since you couldn't use it anyway. I leave all you tube lovers to experiment with this idea and to use your common sense about which settings are correct for each triode.

Some Guidelines:
1) Heat the filament for about 10 minutes with around 40-50% more than the rated value.

2) Drop down to around 20% overrated filament voltage, then,

3) Add plate voltage until your milliamp meter does not rise,
i.e. max current, and the plate shall glow red!!!

4) Keep your eyes on the meter until current falls and immediately switch off!

In the old days there were special tube rejuvenators on the market, but nowadays you will have to build it yourself!


Note: Enjoy the Music.com highly encourages our readers to buy the Sound Practices CD filled with all 16 issues in high quality format from publisher/editor Joe Roberts' eBay store by clicking here. What is below is merely a small sampling of the many great articles within the CD.











































Quick Links

Audiophile Review Magazine
High-End Audio Equipment Reviews


Equipment Review Archives
Turntables, Cartridges, Etc
Digital Source
Do It Yourself (DIY)
Cables, Wires, Etc
Loudspeakers/ Monitors
Headphones, IEMs, Tweaks, Etc
Ultra High-End Audio Reviews


Enjoy the Music.TV


Editorials By Tom Lyle
Viewpoint By Roger Skoff
Viewpoint By Steven R. Rochlin
Various Think Pieces
Manufacturer Articles

Show Reports
AXPONA 2023 Show Report
Salon Audio Montréal Audiofest 2023
CanJam Singapore 2023 Report
Florida Intl. Audio Expo 2023
Capital Audiofest Show 2022
KL International AV Show 2022
Toronto Audiofest Show 2022
CanJam SoCal 2022 Show Report
Pacific Audio Fest 2022 Report
T.H.E. Show 2022 Report
HIGH END Munich 2022
...More Show Reports


Audiophile Contests
Cool Free Stuff For You
Tweaks For Your System
Vinyl Logos For LP Lovers
Lust Pages Visual Beauty


Resources & Information
Music Definitions
Hi-Fi Definitions


Daily Industry News

High-End Audio News & Information


Partner Print Magazines
Australian Hi-Fi Magazine
hi-fi+ Magazine
HiFi Media
Sound Practices
The Absolute Sound
VALVE Magazine


For The Press & Industry
About Us
Press Releases
Official Site Graphics


Contests & Our Mailing List

Our free newsletter for monthly updates & enter our contests!




Home   |   Industry News   |   Equipment Reviews   |   Press Releases   |   About Us   |   Contact Us


All contents copyright©  1995 - 2023  HighEndAudio.com and Enjoy the Music.com®
May not be copied or reproduced without permission.  All rights reserved.