Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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 8th March 2007, 06:39 AM   #1
Nixie is offline Nixie  Canada
Banned
 
Join Date: Jan 2006
Location: Vancouver, BC
Angry Repair vacuum tubes?

I have two ancient GE-KR9 and two GE-KR9A Kenotron rectifiers. I got them to use for my [censored by diyaudio policy on HV stuff], but I now noticed one of the tubes has a crack in the ribbed section. I put cyanoacrylate glue on it but I'm guessing vacuum has already been lost.

My question is twofold--can I on a mere propane torch flame fix the crack, and can I reestablish sufficient vacuum from a water aspirator (I can run ice water through it with a pump and the cold water has pretty low vapor pressure)? Also, about dropping in some getter material?

Alternatively, I'll trade these tubes for a solid state bridge or discrete rectifiers that can rectify 130 kV RMS AC at 25 mA DC.
  Reply With Quote
Old 8th March 2007, 08:28 AM   #2
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Hi

You can normally melt glass with a propane flame, but you've to be sure there is already the atmospheric pressure inside, otherwise it will form a bubble that will blow inside.
Restoring the vacuum is much more difficult: most tubes require a hard vacuum, that can only be attained by diffusion or turbomolecular pumps.
LV
  Reply With Quote
Old 8th March 2007, 08:38 AM   #3
Nixie is offline Nixie  Canada
Banned
 
Join Date: Jan 2006
Location: Vancouver, BC
I was under the impression that the getter material will complete the vacuum as all seals leak a bit over time. In light of this, why is a hard vacuum needed initially, when it's the getter that maintains it in most tubes?
  Reply With Quote
Old 8th March 2007, 11:02 AM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
If you've got a crack, the getter is gone. The getter does not have the capacity to convert a poor vacuum to a hard one, it is useful for taking an already good vacuum into a superb one. At minimum, you'd have to evacuate to a micron or so using a rough pump/diffusion pump combo, use glass-blowing methods to seal up the tube, then flash the getter (already been done when the tube was first made, so you're SOL).

Cyanoacrylate will pass air like a colander passes water.
__________________
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it." Upton Sinclair
  Reply With Quote
Old 8th March 2007, 06:19 PM   #5
Nixie is offline Nixie  Canada
Banned
 
Join Date: Jan 2006
Location: Vancouver, BC
I can do resealing since the nipple is quite large, and I can easily stretch it out even more. But looks like I can't reach sufficient vacuum.

Finding solid state rectifiers that can meet my requirement is proving difficult. I see very cheap 20 kV 10 mA diodes on eBay, but I'd need a 100 in parallel/series to make a bridge with sufficient overhead in current and voltage... Higher voltage and current ones are very expensive. It's cheaper for me to wind a filament transformer for these old tubes than to buy the expensive solid state rectifiers, and is why I'm so interested in fixing there.

Anyone know if there's a place that can fix tubes, i.e. can do sufficient vacuum and maybe replace the getter? I can get the glass repaired no problem by a retired scientific glassblower I know for next to nothing, but he doesn't have vacuum.

Click the image to open in full size.
  Reply With Quote
Old 8th March 2007, 09:23 PM   #6
diyAudio Member
 
tomtt's Avatar
 
Join Date: Aug 2002
Location: kansas city mo, and on occasion, around the world ...
Blog Entries: 15
i've seen , where refrig- and ac compressors,were/ are used

for 'vacuum forming'

less $$ than-

http://www.torontosurplus.com/redire.../mys/mys80.htm


how well this would work, i don't know.


at least give this a try.
  Reply With Quote
Old 8th March 2007, 09:29 PM   #7
Nixie is offline Nixie  Canada
Banned
 
Join Date: Jan 2006
Location: Vancouver, BC
A water aspirator such as I have can achieve 10 mm Hg with very cold water. How much lower do I actually need, if I add more getter in the tube?
  Reply With Quote
Old 8th March 2007, 09:42 PM   #8
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Get it down to a micron or two and then we can talk.
__________________
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it." Upton Sinclair
  Reply With Quote
Old 8th March 2007, 09:59 PM   #9
Nixie is offline Nixie  Canada
Banned
 
Join Date: Jan 2006
Location: Vancouver, BC
Explain, SY, why not just putting in more getter wouldn't work? How much gas exactly can a given amount of getter absorb? It seems to me that you figure out how much the amount of gas left in the tube is with the partial vacuum, and then put enough getter to absorb it all. What am I missing?
  Reply With Quote
Old 8th March 2007, 10:03 PM   #10
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Time and quantity. Remember, you're not going to be able to flash the getter, you'll have to rely on Boltzmann and a relatively poor surface area.

If I can get to it tonight, I'll send you some references.
__________________
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it." Upton Sinclair
  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
DIY vacuum tubes! sss Tubes / Valves 1 17th January 2008 12:49 AM
vacuum tubes smak Swap Meet 2 25th January 2006 05:44 PM
Cooling of Vacuum Tubes Gunders Tubes / Valves 19 18th July 2003 01:12 AM


New To Site? Need Help?

All times are GMT. The time now is 12:41 AM.


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