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


It is currently Sep Sat 22, 2018 11:49 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 31 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Tube tester showing "false" short
PostPosted: Jan Sat 13, 2018 10:15 pm 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
Hi! I have a Superior Instruments Co. model TV-11 tube tester. It works perfectly, there is nothing wrong with it as far as I know. It's been recapped and looked over. One thing I always wondered about, was when testing a lot of dual section triode tubes and other dual section tubes, during the shorts test, There is constantly a solid short showing on lever 8 (pin 8 on tube) and when switched to the other section, often lever 3 (pin 3 on tube) then shows the same short. The tubes test good and some are NOS and others used, so they can't all be bad. I'm wondering, what causes this short to show up? It must be something common to both sections within the tube i'm thinking. It's not mentioned on the roll chart. Not all tubes do it, such as a 6J6, 6V6, etc. Just some types, such as a 12A*7, etc. Just wondering if anything is wrong with the tester circuit. Does anyone else with a TV-11 have this problem show up? Thanks for the help!


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sat 13, 2018 11:08 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11761
Location: Mpls, Minnesota
Is the Load control turned fully clockwise when doing the shorts test?

Dave


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sat 13, 2018 11:15 pm 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
Yes it is. The short light behaves normally testing other levers, but shows a short on the levers I mentioned, one depending on what side of the tube i'm testing, and as I said, happens only on certain (mostly dual section) tubes. Such as 6SN7, 12AX7, etc.


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sat 13, 2018 11:27 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2271
Location: Spring Hill, FL
On 12A*7 family tubes, pin 3 is the cathode of one side, and 8 the cathode of the other. So for some reason, it's the cathodes. But why it would do that, I'm not sure. On those tubes, the heater is pins 4 and 5, with 9 being a center tap, so you should see a short when you throw lever 9. Does that happen?

_________________
Michael


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sat 13, 2018 11:44 pm 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
Interesting. On this tester, lever 9 is in the "N" position, so I don't test that one for a short. I also noticed, this mysterious cathode short on these tubes only shows up when the cathode is hot. If I turn the filament off, the short goes away. Any idea why this would happen and what is causing it? Are these tubes defective?


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 12:18 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 33212
Location: Maryland 20709, USA
CrankTelephone101 wrote:
I also noticed, this mysterious cathode short on these tubes only shows up when the cathode is hot. If I turn the filament off, the short goes away. Any idea why this would happen and what is causing it? Are these tubes defective?

If it was really a short in the tube, it would persist for tens of seconds after removing the filament voltage, until the cathode cooled down. It's not a real short.

- Leigh

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 12:22 am 
Member
User avatar

Joined: Oct Fri 28, 2016 10:56 pm
Posts: 29
Location: Midland, TX
I have a Jackson 684S that was showing a short in a couple of particular button positions. I FINALLY tracked it down to the 7 pin subminiature socket. At some point it had arced between a couple of pins creating a carbon path that was enough to show a short when testing a tube. I disconnected the wires to those pins and the short disappeared.

It's a long shot but check out that socket.

Alan


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 12:30 am 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
Leigh wrote:
CrankTelephone101 wrote:
I also noticed, this mysterious cathode short on these tubes only shows up when the cathode is hot. If I turn the filament off, the short goes away. Any idea why this would happen and what is causing it? Are these tubes defective?

If it was really a short in the tube, it would persist for tens of seconds after removing the filament voltage, until the cathode cooled down. It's not a real short.

- Leigh

It actually does slowly fade out as the cathode cools, but I wouldn't imagine ALL of my 12A*7 tubes are defective. I have tons of them, a bunch of used ones, and NOS ones, and any one I have ever tested has shown this "short". They all test fine into the green. I'm just wondering what is causing the short on the cathodes. And I don't understand why it only seems to show up on these dual section type of tubes. Tubes such as the 6BA6, 6V6, 5Y3, etc. don't show any abnormal shorts.


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 12:33 am 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
N5NA wrote:
I have a Jackson 684S that was showing a short in a couple of particular button positions. I FINALLY tracked it down to the 7 pin subminiature socket. At some point it had arced between a couple of pins creating a carbon path that was enough to show a short when testing a tube. I disconnected the wires to those pins and the short disappeared.

It's a long shot but check out that socket.

Alan

Interesting observation! I will look into it, but I don't think that is what's causing it since it doesn't do it on all tubes, only some types. 5Y3, 6V6, 6BA6, 12AX4, etc. all test fine with no shorts, while others, mostly dual section types, have this issue, but not all dial section tubes, but most of them. Tubes like the 12AX*7, 6U8, 6GH8, etc. have the "short".


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 12:37 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11761
Location: Mpls, Minnesota
Perhaps you tester is too sensitive, did you replace the capacitor in the shorts test section with the proper value? Did you check the resistors in this section? Clean the toggle switch (#8) and the tube socket with alcohol and see if that helps.

Dave


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 12:57 am 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
easyrider8 wrote:
Perhaps you tester is too sensitive, did you replace the capacitor in the shorts test section with the proper value? Did you check the resistors in this section? Clean the toggle switch (#8) and the tube socket with alcohol and see if that helps.

Dave

Could be, but I don't think so. I checked and replaced all capacitors, and all the resistors checked out pretty good. When I got the tester I cleaned the switches real good. And it also happens with octal tubes, so it's not the socket. Could it be a wiring error somewhere from the factory? I'm still wondering if anyone else with a TV-11 has this issue.


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 2:17 am 
Member
User avatar

Joined: Dec Tue 01, 2015 5:31 am
Posts: 1622
Location: Columbus Ohio
Did you happen to replace the diode, BY1 rectifier? I see a schematic where it says it's drawn backwards.
Looks like 2 caps. both in correct?

_________________
Joe - There's no shortage of cruelty to animals: http://joinASPCA.org


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 2:31 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11761
Location: Mpls, Minnesota
The diode is not used for the shorts test, it is out of the circuit.

Dave


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 8:22 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2271
Location: Spring Hill, FL
If you figure this one out, please fill us in because this one is screwing with my mind now.

_________________
Michael


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 6:22 pm 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
glue_ru wrote:
Did you happen to replace the diode, BY1 rectifier? I see a schematic where it says it's drawn backwards.
Looks like 2 caps. both in correct?

I haven't replaced it. And I took it apart last night and found that I did not replace the .5 uf cap, but I don't see how this one cap could cause this issue, as the other levers do the shorts test fine, and most tubes don't have this issue anyway. The other cap is in correctly.


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 6:25 pm 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
TPAairman wrote:
If you figure this one out, please fill us in because this one is screwing with my mind now.

I certainly will. I am very puzzled by this and curious about it. I wonder if anyone else with a TV-11 could reproduce this issue or if it's a problem with my tester? Could it be a wiring error of sorts? I found a resistor going to one of the condenser test jacks to have never been soldered from the factory! I will have to solder that just for the heck of it.


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Sun 14, 2018 8:15 pm 
Member
User avatar

Joined: Dec Tue 01, 2015 5:31 am
Posts: 1622
Location: Columbus Ohio
its not so much that those components will cause the issue as getting in and checking any work and other connections.
Check wiring socket to socket for shorts, burned insulation, tube pins hitting leads below a socket.

_________________
Joe - There's no shortage of cruelty to animals: http://joinASPCA.org


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Mon 15, 2018 2:25 am 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
That's true! I checked everything over, and everything seems intact and untouched. I cleaned the switches, the tubes socket wiring is good and the tube sockets are tight, so the tester doesn't seem to have had a lot of use anyways.


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Mon 15, 2018 2:37 am 
Member

Joined: Sep Tue 30, 2014 6:08 am
Posts: 3040
Location: The Old Dominion VA 23518
CrankTelephone101 wrote:
Could be, but I don't think so. I checked and replaced all capacitors, and all the resistors checked out pretty good. When I got the tester I cleaned the switches real good. And it also happens with octal tubes, so it's not the socket. Could it be a wiring error somewhere from the factory? I'm still wondering if anyone else with a TV-11 has this issue.


What did you clean the switches with? Many cleaners leave a residue that could affect the leakage/shorts function.

The residue often will provide a parallel path, reducing leakage values....and creating a problem.

_________________
Brian
"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


Top
 Profile  
 
 Post subject: Re: Tube tester showing "false" short
PostPosted: Jan Mon 15, 2018 2:52 am 
Member
User avatar

Joined: Nov Sun 22, 2015 9:07 pm
Posts: 550
Location: Chicago, IL
When I first got the tester, I cleaned them with regular contact cleaner, and oiled them with 3-in-1 oil, since they were stiff. I also cleaned and oiled the shafts of the pots. This tester had this problem before I did any work to it though, and it's all original as far as I can tell, besides the cap I have replaced. The shorts circuit works great other than this one issue.


Top
 Profile  
 
Post New Topic Post Reply  [ 31 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: dholland, Majestic-12 [Bot], TechyMechy and 8 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB