Tube rejuvination - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th January 2012, 11:19 PM   #1
diyAudio Member
 
thaumaturge's Avatar
 
Join Date: Aug 2011
Location: Utah
Default Tube rejuvination

In broadcasting, a fairly standard practice for squeezing an extra bit of life out of a very expensive tube whose emissions have dripped off is to up the fillament voltage say 10% and let it cook about 12 hrs with no HV applied. This seems to somehow free up a bit more cathode material. At multiple thousands of dollars each even an extra six months of time is worth a little effort.

My question is has anybody tried a similar practice with audio tubes and if so what were the results?

Doc
__________________
Ne timeas a facie mulierum ea ignorare
  Reply With Quote
Old 5th January 2012, 08:07 AM   #2
diyAudio Member
 
Join Date: Jul 2008
I've tried raising the tension even more (50%) but just for shorter periods, 30-60 seconds. It works pretty well on some tubes, but has no effect on others, depending on type and quality, I guess.
  Reply With Quote
Old 5th January 2012, 09:23 AM   #3
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
I believe this just works with directly heated tubes. The higher heat causes some of the thorium to come to the outside of the cathode where it has been depleated.
  Reply With Quote
Old 5th January 2012, 09:40 AM   #4
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The same trick was used for indirectly heated CRTs.
  Reply With Quote
Old 5th January 2012, 04:57 PM   #5
diyAudio Member
 
thaumaturge's Avatar
 
Join Date: Aug 2011
Location: Utah
Thanks for your replies. I know the cathodes are different in smaller glass envelope tubes. I knew that the main cathode material was thoriated tungsten. In broadcast tubes I've seen amazing results from the rejuvination process. Saw a Klystron that was basically dead come back to life and live another year and a half. At $36,000 ea. that was significant.
Doc
__________________
Ne timeas a facie mulierum ea ignorare
  Reply With Quote
Old 5th January 2012, 05:35 PM   #6
iko is offline iko  Canada
diyAudio Moderator
 
iko's Avatar
 
Join Date: May 2008
Location: Toronto
Got some direct heated transmitting tubes and a bunch of them have the following issue. With the heater on and 0V on the grid, when I bring up B+ there is very little current passing through. At around 300V on the anode a purple/bluish glow appears at the bottom of the tube and the current through the tube goes up abruptly. Looked around the net and found some advice on tube rejuvenation which involved baking the tube for 12 hours or so at about 100C, which I did, last night. But it didn't help even one tube. The tube needs 5V/7.5A for the heater, so I also tried to give it 10V for a few minutes. Tough tube, the filament didn't die; the plate was nice and red.

Not sure what else I can try. Any advice?
  Reply With Quote
Old 5th January 2012, 05:47 PM   #7
diyAudio Member
 
thaumaturge's Avatar
 
Join Date: Aug 2011
Location: Utah
Run the filament up to 5.5 volts and let it cook a day. No HV on. Check for emmission then repeat. But it may not be emmission but a gas problem. Depending on the tube, you might check to see if they are rebuildable. Some are. Surprisingly you get better results out of rebuilt tubes because they run much longer without gassing up because all the components are pretty much through outgassing. Basically they just replace the filaments then resuck a vaccuum and reseal.
Doc
__________________
Ne timeas a facie mulierum ea ignorare
  Reply With Quote
Old 5th January 2012, 05:59 PM   #8
iko is offline iko  Canada
diyAudio Moderator
 
iko's Avatar
 
Join Date: May 2008
Location: Toronto
I'll give it a try. The tube is 4E27.
  Reply With Quote
Old 5th January 2012, 06:14 PM   #9
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally Posted by ikoflexer View Post
Not sure what else I can try. Any advice?
It would help to know the type/number of the tube in question. However, the symptom you describe is a large amount of gas that most likely makes the tube unredeemable. However, with certain smaller types, I have had fair to good results with this treatment. First, make a diode out of the tube by connecting the grids and plate together. Next, light the tube filaments to the normal level. Then, apply 120 volts AC across the tube (cathode to plate) in series with a 60 or 100 watt light bulb and let it run for several hours. If the bulb grows dimmer, the gas is recombining inside. You may also need to apply forced air cooling with an external fan and chimney setup depending on the tube type. Use an isolation transformer if you're squeamish about the AC.

edit: I just saw that it's a 4E27. Those are very old. If the bottom of the tube has green glass, these are always leaky and almost never work out well. And if they're anything other then Eimac, forgetaboutit.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell

Last edited by HollowState; 5th January 2012 at 06:21 PM.
  Reply With Quote
Old 5th January 2012, 07:30 PM   #10
diyAudio Member
 
thaumaturge's Avatar
 
Join Date: Aug 2011
Location: Utah
My question answered, this thread now up for sale... grabs... whatever.
Doc
__________________
Ne timeas a facie mulierum ea ignorare
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
need diy tube preamp (line-stage) recommendation and general tube advice Musiclover4 Tubes / Valves 16 18th May 2013 03:19 PM
FS: DIY Tube parts, tubes 845's teflon, tube phono PCBs tronan Swap Meet 4 3rd December 2011 01:19 AM
Telefunken Tube Receiver, Magnetophon 97 (Tube R2R) and Record Player Dredfred Swap Meet 1 3rd April 2011 01:12 AM
FS tube tuner, Active filter kit, tube amp, amp3 Josephjcole Swap Meet 9 20th July 2007 04:05 PM
SS or tube voltage amplifying stages in an amp with tube output? ray_moth Tubes / Valves 14 4th July 2007 03:09 AM


New To Site? Need Help?

All times are GMT. The time now is 06:33 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2