Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Oct Sat 21, 2017 11:07 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 14 posts ] 
Author Message
 Post subject: Fixing tubes with open filaments....
PostPosted: Oct Sat 29, 2016 2:04 am 
Member

Joined: Jan Mon 28, 2013 9:35 pm
Posts: 761
Location: Santa Rosa, CA
....sometimes.

This is an old trick but worth repeating. Occasionally tubes that appear to
have open filaments really don't. The solder joint(s) at the pins can be cracked,
have poor solder joints or the wire has enough corrosion to cause the connection
to be poor. The solution is melting the solder on each filament pin, remove
old solder with a solder sucker then clean the wires and pins as much as
possible before applying new solder. I'll usually use a small amount
of rosin to help the new solder adhere.

I've resurrected old and newer tubes this way. Today it was an Eimac 250T
which is getting to be an expensive tube.

This doesn't work very often but its worth a try with octal and pre-octal
tubes as well as larger tubes that have soldered pins. No, this won't work
with compactrons or 7 & 9 pin tubes.
Steve


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Sat 29, 2016 4:40 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11288
Location: S. Dartmouth MA 02748-1225 USA
Steve,

The early tubes used a high tin solder. The tin develops a corrosion and the joint to the tube wire element breaks away. The high tin solder will be difficult to melt, so much so the additional heat can blister the Bakelite tube base. The trick is to file some of the tin off the end of the pin, add active rosin flux, then apply fresh solder, the fresh solder will amalgamate with the tin and allow easy extraction of all the tin and solder, lowered melting point. Using an Exacto knife with the pointed blade to scrape the inside of the pin and the sides of the element wire. applying a small amount of flux and re-solder. This technique is particularly useful for salvaging 226's because of the high current filament. Time has caught up to most of the multi-pin tubes too and re-soldering can salvage quite a few.

_________________
There Are None So Blind As Those Who Will Not See: John Heywood, 1546


Last edited by Chas on Oct Sat 29, 2016 3:25 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Sat 29, 2016 4:54 am 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 2339
Location: Tucson, Arizona U.S.A.
Hold the tube with the pins down when soldering. This keeps the solder from running down the outside of the pin. Enough gets inside anyhow to make a good connection.

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Sat 29, 2016 2:14 pm 
Member

Joined: Mar Sat 14, 2009 5:56 pm
Posts: 3826
Location: RI, 02885
There is a procedure for broken filaments also. The success rate of welding a filament is very low in my experience but has extended the life of a few expensive tubes for me. You apply high voltage to the filament pins and tap the tube to try to make the broken ends touch. If all works well, the filament fuses on contact and continuity is restored. I use a charged capacitor as the voltage source since it will discharge immediately so it will not burn the filament out again.
It's pretty much the same procedure I use to restore open audio transformers for my 20's battery sets. I have over a 50% success rate with my audio transformers so far.
You have to use caution handling charged capacitors. If you mishandle them you can receive a severe shock. Use well insulated connectors and make sure you are not grounded. I have a rubber mat in front of my bench that I stand on while working.

_________________
I'm not a hoarder, I'm a caretaker of scarce commodities


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Sat 29, 2016 5:20 pm 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 9096
Location: Santa Rosa, CA
In 1969, we experimented with "fixing" picture tubes (CRT) for Rauland. I was working for Westinghouse and involved with ruby rod lasers.

Rauland had problems with electrode welds that had gone "open" in the neck area. We succeeded in shooting a laser through the glass and re-welding wires that were sufficiently close together.

Problem: the welding vaporized metal that migrated... guess where? On to the CRT phosphor and changed all the colors!

In a receiving tube, you might get lucky with an HV weld and the vapor will just condense on the glass, harmlessly.

Rich


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Sun 30, 2016 3:06 pm 
Member

Joined: Jan Mon 28, 2013 9:35 pm
Posts: 761
Location: Santa Rosa, CA
Bugman wrote:
There is a procedure for broken filaments also. The success rate of welding a filament is very low in my experience but has extended the life of a few expensive tubes for me. You apply high voltage to the filament pins and tap the tube to try to make the broken ends touch. If all works well, the filament fuses on contact and continuity is restored. I use a charged capacitor as the voltage source since it will discharge immediately so it will not burn the filament out again.
It's pretty much the same procedure I use to restore open audio transformers for my 20's battery sets. I have over a 50% success rate with my audio transformers so far.
You have to use caution handling charged capacitors. If you mishandle them you can receive a severe shock. Use well insulated connectors and make sure you are not grounded. I have a rubber mat in front of my bench that I stand on while working.


When using a charged HV cap to attempt to internally weld open windings in
audio transformers you MUST limit the current with an internal resistor or you'll
cause more faults. In my case I use an old TV transformer that puts out about
500 VAC, use a 10 K, 20 watt resistor in series and monitor the primary
current while slowly bringing it up with a variac. This usually doesn't work
but nothing to loose and I have been able to save some fairly rare 1920's
interstage audio transformers this way.
Steve


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Sun 30, 2016 3:27 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11288
Location: S. Dartmouth MA 02748-1225 USA
O.T. No audio transformer is actually saved by creating a noisy carbon path within the windings. Winding resistance will go up, the arc path is not a valid resistor and prone to degradation for acid contamination and noise. I have done the forensics on such "repaired" transformers after getting "smoked" by a seller on a supposed "good" audio transformer. Copper expands by a factor of 67,000 times when it turns from a solid to a vapor.

_________________
There Are None So Blind As Those Who Will Not See: John Heywood, 1546


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Oct Mon 31, 2016 3:01 pm 
Member

Joined: Jan Mon 28, 2013 9:35 pm
Posts: 761
Location: Santa Rosa, CA
Chas wrote:
O.T. No audio transformer is actually saved by creating a noisy carbon path within the windings. Winding resistance will go up, the arc path is not a valid resistor and prone to degradation for acid contamination and noise. I have done the forensics on such "repaired" transformers after getting "smoked" by a seller on a supposed "good" audio transformer. Copper expands by a factor of 67,000 times when it turns from a solid to a vapor.


Sometimes the open winding will weld to an adjacent wire. Like I said this
doesn't work very often but I have had some success. Its a last resort.
Steve


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Nov Tue 08, 2016 2:42 am 
Member
User avatar

Joined: Apr Thu 21, 2011 2:00 am
Posts: 2852
Location: Georgia
Rich, W3HWJ wrote:
In 1969, we experimented with "fixing" picture tubes (CRT) for Rauland. I was working for Westinghouse and involved with ruby rod lasers.

Rauland had problems with electrode welds that had gone "open" in the neck area. We succeeded in shooting a laser through the glass and re-welding wires that were sufficiently close together.

Problem: the welding vaporized metal that migrated... guess where? On to the CRT phosphor and changed all the colors!

In a receiving tube, you might get lucky with an HV weld and the vapor will just condense on the glass, harmlessly.

Rich


I remember seeing a TV commercial on the old CBS series The 21st Century in which they showed a wire within a tube envelope being repaired by laser. I remember Union Carbide did many of the commercials for the show, But I'm not sure.

_________________
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Nov Mon 14, 2016 5:35 pm 
Member

Joined: Mar Sat 28, 2009 8:27 pm
Posts: 691
Location: Georgia
Tubes such as 5U4's etc. often have a heater current of 2 amps or more which can be troublesome for those dipped solder connections on the pins. Back in the 60's a parts salesman gave me a couple of "pin crimpers" made by the Berns company. You insert the heater pin of an octal tube and push down on the handle and it securely crimps the internal wire to the socket pin. This crimping slightly enlarges the tube pin so that it fits more securely in its socket.
I have crimped many tube heater pins over the years using this tool. "Berns PT-1 & PT-2)"


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Nov Mon 14, 2016 5:47 pm 
Member

Joined: Sep Tue 30, 2014 6:08 am
Posts: 1896
Location: The Old Dominion 23518
eeprof wrote:
Tubes such as 5U4's etc. often have a heater current of 2 amps or more which can be troublesome for those dipped solder connections on the pins. Back in the 60's a parts salesman gave me a couple of "pin crimpers" made by the Berns company. You insert the heater pin of an octal tube and push down on the handle and it securely crimps the internal wire to the socket pin. This crimping slightly enlarges the tube pin so that it fits more securely in its socket.
I have crimped many tube heater pins over the years using this tool. "Berns PT-1 & PT-2)"


Somewhere around here, I have a well worn Berns....


Attachments:
berns.jpg
berns.jpg [ 57.71 KiB | Viewed 2731 times ]

_________________
Brian
"Capacitor Cosmetologist since 1979"
USN Retired (Avionics)
Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Nov Mon 14, 2016 5:58 pm 
Member

Joined: Mar Sat 28, 2009 8:27 pm
Posts: 691
Location: Georgia
That ad is exactly referring to the tools I have. The Berns PT-2 is made to crimp RCA phono plugs so that you do not have to solder them and it works for the older style vacuum tubes.


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Jan Mon 09, 2017 11:42 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3389
Location: Olympia WA USA
The Berns pin crimp tools originally came in 5 sizes. I have looked for decades and even run WTB ads here for the other sizes. I found one for the CRT pins/octal pins, but still looking & hoping to find the full set before I die.
I crimp the pin, then run solder into it. Works like a champ!

_________________
FrankB
WB7ELC
Member: TCA & Steel Soldiers.
" Break down the wall"


Top
 Profile  
 
 Post subject: Re: Fixing tubes with open filaments....
PostPosted: Jan Wed 11, 2017 2:17 am 
Member

Joined: Mar Sat 14, 2009 5:56 pm
Posts: 3826
Location: RI, 02885
I have attached pix of the two crimpers I have from a clean-out of an old radio-TV shop. I wondered for years as to their function and kept them in an odd parts box. Thank you for opening this phase of the discussion. I can now put these devices to use should the need arise.


Attachments:
P1120569.JPG
P1120569.JPG [ 91.22 KiB | Viewed 2205 times ]

_________________
I'm not a hoarder, I'm a caretaker of scarce commodities
Top
 Profile  
 
Post New Topic Post Reply  [ 14 posts ]  Moderator: Chuck Schwark

All times are UTC [ DST ]


Who is online

Users browsing this forum: cl350rr and 2 guests



Search for:
Jump to:  




















Privacy Policy :: Powered by phpBB