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valve tester

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colin55

Well-Known Member
I must have replaced over 2,000 values in 15 years of doing 35,000 TV repairs.
I must have replaced only a dozen valves that did not light up.
The most common problem was a cracked 6CM5 or 6AL2. If these valves were left standing for 2 weeks, they cracked. Don't ask me why.
Tandy had valve testing machines. What an absolute joke. You can't test a valve.
They become "knocky." They become weak, they become "microphonic," they become noisy. Only a circuit will show the fault. A valve may work in one circuit but not another.
It's very unwise to use a second-hand valve. You don't know why it has been disgarded. Some circuits need extra gain, that's why there's 12AU7 and 12AX7.
 

Andy1845c

Active Member
well I'm selling them locally directly to a private buyer

You don't happen to have any 6JS6's do you?

I have been trying to get my old ham radio transmitter back on the air, and can't get much power out of it. Its old and uses valves. I am thinking I may have one that has gone bad.

I was actually just researching how to test valves yesterday. This topic came up at a good time for me. :D

My dad has several of those suitcase style valve testers in his basement. But as Rolf said, I am sure they need some TLC before they are going to work again.
 

Thunderchild

New Member
You don't happen to have any 6JS6's do you?

I have been trying to get my old ham radio transmitter back on the air, and can't get much power out of it. Its old and uses valves. I am thinking I may have one that has gone bad.

I was actually just researching how to test valves yesterday. This topic came up at a good time for me. :D

My dad has several of those suitcase style valve testers in his basement. But as Rolf said, I am sure they need some TLC before they are going to work again.

erm your a bit far away aren't you ? I can check with my dad if you really want them but he's already negotiating with a buyer but with 500+ valves a couple won't make any difference unless he's after those specificly
 

Andy1845c

Active Member
Yes, I am quite a ways from the UK. Just thought i'd ask incase you had a bunch of them or something. They are used as the final tubes in my transmitter and are out of production and a bit hard to find.
 

Boncuk

New Member
The only thing which can go wrong with a tube is the cathode. It is coated with barium which produces a "cloud" of electrons when heated. The electrons move towards the positive anode controlled by the grid.

Reducing the filament heating power will not be satisfactory when testing a tube.

You can refresh a tube by applying high voltage to the cathode and the grid to burn off the used barium.

This procedure requires close watch. After that the tube might be completely worthless :mad: or work like new. :)

Boncuk
 

Mikebits

Well-Known Member
The only thing which can go wrong with a tube is the cathode. It is coated with barium which produces a "cloud" of electrons when heated. The electrons move towards the positive anode controlled by the grid.

Reducing the filament heating power will not be satisfactory when testing a tube.

You can refresh a tube by applying high voltage to the cathode and the grid to burn off the used barium.

This procedure requires close watch. After that the tube might be completely worthless :mad: or work like new. :)

Boncuk

There is much more than the cathode that can fail. Screen grids break, filaments open, Plates open. Being that the tube is somewhat mechanical in connection, many things can fail.
 

flat5

Member
Elements can twist and short (or shout, microphonics) or just change the characteristics. Solder connections can open at the base. Sockets can go bad and THAT can drive you crazy.
I had a rough time with a Yellow Cab early 1960s design transceiver with a bad socket. Low output power. Grounds were all good. As last resort I changed the socket. Lost a lot of time on that one.
 

duffy

Well-Known Member
I must have replaced over 2,000 values in 15 years of doing 35,000 TV repairs.
I must have replaced only a dozen valves that did not light up.


I must have replaced over 20 valves in my 1 year of doing 35 TV repairs.
I must have replaced one that did not light up.

They almost always light the filament. What goes wrong is a mystery. A transistor will short or open, a vacuum tube gets creative.
 

Thunderchild

New Member
Yes, I am quite a ways from the UK. Just thought i'd ask incase you had a bunch of them or something. They are used as the final tubes in my transmitter and are out of production and a bit hard to find.

sorry I just got dad to check his list and he hasn't got any, he has manily radio valves
 

Video Warrior

New Member
Elements can twist and short (or shout, microphonics) or just change the characteristics. Solder connections can open at the base. Sockets can go bad and THAT can drive you crazy.
Let's not overlook when they "get gassy" - as in lose some or all of that vacuum. Usually you *will* lose the heater when that happens. Not always though.
 

Andy1845c

Active Member
sorry I just got dad to check his list and he hasn't got any, he has manily radio valves

Okay, well, thank you and please thank him for checking. :)

eBay search comes up with 4 hits:
6JS6, Electronics items on eBay.com

Oops, just scrolled down. I mean "8 hits".

Thanks for the heads up. I need a matched set of 2 though. I only see one pair of them listed and it doesn't say if they match.

I am actually not sure if I need them at the moment or not, but them being out of production tells me I should keep an eye open for them.
 

Andy1845c

Active Member
Since this topic is already kinda off topic, i'm going to just ask....

What causes the top of a valve to get shiny? Does it have to do with metal migrating up there over time, kind of like a fluorescent lightbulb gets black on the ends? Is the amount of shine dependant on the amount of use a valve has had?
 

awright

Member
Two suggestions for finding a tube tester to use:

1. Call all the local electronics supply stores (if there are any in your area) to ask if they have a tube tester. Al Lasher Electronics here in Berkeley, an electronics parts retailer that has been in business for many decades, still has a tube tester accessible to the public. When I was in the store a week or two ago a guy was settled in with several bagfulls of tubes, just plugging away.

2. Contact your local ham radio club. The old-timers who built their own transmitters and receivers, as opposed to the appliance operators who dominate the hobby today, worked a lot with tubes. They would love to strut their stuff.

While possible, building your own tester would be a large task for a non-expert, largely due to the wide variety of filament and plate voltages required, current limiting required for safety, and interpretation of the results required. All the switches or plug-in cards and the array of sockets made those selections for you. You'd have to do a lot of research just to find out the proper test conditions for each tube type.

I believe that most of the old public access tube testers simply applied filament and plate voltages, and determined whether the cathode still emitted enough plate current. They either ignored the grids and screens in tetrodes and pentodes or tied them to the plate for the test. (That's interesting and a sign of the times. This ELECTRONICS website tags "tetrode" and "pentode" as spelling errors!)

andy1845c, the shiny area is the "getter" metal that is vaporized off an auxiliary part of the tube at the last stage of manufacturing. The evacuation process is imperfect. The getter metal vapor trapped some of the remaining air molecules as it condensed onto the wall of the tube. If you look inside the tube envelope you will see a metal ring standing on a post that does not connect to the outside world. That metal ring was heated by induction from outside the tube to vaporize the getter metal on it.

(We're dating ourselves, guys.)
 
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ecerfoglio

New Member
Since this topic is already kinda off topic, i'm going to just ask....

What causes the top of a valve to get shiny? Does it have to do with metal migrating up there over time, kind of like a fluorescent lightbulb gets black on the ends? Is the amount of shine dependant on the amount of use a valve has had?


They build (built?) a "second filament" inside the valve, and after the glass bulb is evacuated and sealed this second filament is heated with a strong RF field and vaporizes.

The metal vapors capture any residual oxigen and make a "better" vacuum inside the valve.

In the process some (nearly all) off the second filament's metal gets on the glass and is the shiny top you see in the valve.

EDIT: awright beat me with his edit
 
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Video Warrior

New Member
Yep, blame the getter for that shine. Although I did at one point have this *giant* triode with a 4-pin base that actually had mercury rolling around inside of it. Could get a nice shiny film of that going if you worked at the tube long enough. Wish I remembered the number on the side of it...
 
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