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Can I Test Old Vacuum Electron Tubes a simple way?

Richard King

Diamond
Joined
Jul 12, 2005
Location
Cottage Grove, MN 55016
I just bought a box of Old radio / TV / Audio Equipment Electronic tubes and I am wondering if I can use a regular meter to test to see if they are good? I have RCA, ITT, Hytron, GE, etc. They all are in boxes 1"x 1" x 4" long. I want to sell them, but don't want to sell junk. I remember going to the drug store when I was a kid to test them... a thing of the past......Rich
 
Well, you could buy a tube tester. The quick solution is to look for metallic deposits inside the glass, indicating prior use. Then look for broken (vibrating wildly when bumped) filaments. Then sell them as is. The buyer will have a tube tester.

Larry
 
Well, you could buy a tube tester. The quick solution is to look for metallic deposits inside the glass, indicating prior use. Then look for broken (vibrating wildly when bumped) filaments. Then sell them as is. The buyer will have a tube tester.

Larry

Sorry, neither of those is correct. All have a dark shiny spot in them from the "getter". This is a material that after the tube is made triggered by heating. The molten cloud grabs any remaining air molecules and deposits itself on the inside of the envelop. If the spot has turned white, then the tube is leaking air and is no good.

You will not find any vibrating or waving filaments like a light bulb, the filaments are durable structures. You can check continuity with an ohmmeter. Plug the tube number into google and bring up the internal connections. Remember that the tube diagram is as shown from the top. You will be looking at it from the bottom, hence all the numbers will be backward.

Tom
 
I just bought a box of Old radio / TV / Audio Equipment Electronic tubes and I am wondering if I can use a regular meter to test to see if they are good? I have RCA, ITT, Hytron, GE, etc. They all are in boxes 1"x 1" x 4" long. I want to sell them, but don't want to sell junk. I remember going to the drug store when I was a kid to test them... a thing of the past......Rich

If they are in new boxes, the chances are they are new. This is especially true of RCA tubes from the 30s because they were having so much trouble with fakes and people putting used tubes in new boxes that they started stapling them in. I don't know when they stopped but they were not doing it after WWII when I started working with radios. The tests can be on several levels. The first is to look for the mirror coating on the glass. This is metal evaporated onto the glass after evacuating and sealing, referred to as the "getter". The pumpdown was not really that good, partly because they didn't want to take the time to get the vacuum that far down and partly because gasses were adsorbed in the metal elements and would work their way out later. Because the getter was formed by heating the material to its boiling point, there was little or no gas adsorbed in it, so it picked up residual gasses and increased the vacuum to a better value. If a tube has a good vacuum, the getter is bright. If air has leaked in, it will be a chalky white and the tube is inoperable.

The next check is filament continuity, which you can do with an ohmmeter. Touch the test leads to the filament pins and see if you get a reading. If you do, the odds are high that the tube is good. If you need the base diagrams, send me a list at [email protected] and I will scan the appropriate diagrams for you.

The next level of test is an emission test. This involves lighting the filament (called a heater in indirectly heated cathode tubes) and measuring the electron flow between the anode and cathode. That is what most tube testers do and is a fair amount of work to set up if you do not have one. The best testers, notably Hikok Dynamic Mutual Conductance testers, actually hook the tube up as an amplifier and measure the gain. These are the highest level testers and were not used in drug stores and Radio Shacks.

Unless you find someone with a tester, probably the best course is to stop with filament continuity.

I have to relate my favorite tube testing story. A really classy couple I met at an antique radio convention, two of the nicest people I know, met because the girl was watching her brother work on a TV set. He asked her to go to a Radio Shack and buy a replacement tube if needed. He said they would test the tube for her. The salesman at the Radio Shack was a between jobs EE, filling in while he job hunted. She went up to him and asked him to test the tube. He did, then married her.

Bill
 
Try to find someone with a tube tester. There is really no other way to completely test a vacuum tube and even that does not mean they will work in every application. You might try a TV service shop if you can find one or some one who is still into tube type audio amplifiers. There is an emerging market for tube audio. The testers found in public places were relatively simple to operate but some of the professional models were more complex. I have acquired probably over 800 tubes in the last several years. I sold 2 tube testers last year - no I did not test 800 tubes. They are around but not so common any more. Good luck.

Bob
WB8NQW
 
Remember that the tube diagram is as shown from the top.
You will be looking at it from the bottom, hence all the numbers will be backward.
Incorrect.

Except for the very first tube manual (RCA R-10 and Cunningham C-10), all tube base diagrams are shown as viewed from below, i.e. looking at the socket with the radio turned upside down as it would be for service / repair.

- Leigh
 
I just bought a box of Old radio / TV / Audio Equipment Electronic tubes and I am wondering if I can use a regular meter to test to see if they are good?
Hi Richard,

The fact that they're in boxes does not mean that they're new.

TV repair guys doing home service calls always(?) put the bad tube in the box from the new tube and took it back to the shop. What happened then depends on the shop.

I would suggest categorizing them as to probable application.

The first number in the tube type is the filament voltage, like 5Y3, 6AK5, 12SK7, 50C5, etc.

The types that may have some value start with 5, 6, 7, 12, 14, 35, or 50.

Other values are almost certainly TV tubes, which are virtually worthless.

Any metal-cased tubes will likely have some value.

I might suggest you join the Forum at AntiqueRadios.com
With the exception of one sub-forum, that whole site is about tube radios etc.

The Classifieds section there is the appropriate place to sell the tubes.

You could ask for help from anybody in your neighborhood.
They're a very friendly and helpful bunch.

- Leigh
 
Gotta find somebody with a tube tester. It may or may not be worth it. The audio folk will pay sometimes incredible amounts for certain tubes, but the vast majority of old "TV" tubes are near to worthless. If you have 12AX7, 5U4 or any of the popular power tubes, EL34, KT88 (going by memory) it might well be worth it. I think a good 300B is over $1k now. Brand matters a lot, so do some searches on the specific numbers.
 
The short story is that there is essentially NO way for you to determine goodness without test equipment.

I am an old fossil and can design tube circuits, etc. I would not try to hook up some sort of tester, which is why I have 2 commercial ones.

Do as suggested and move them on to someone who wants to take on the job.

Yes, 12AX7, 12AU7, 12AT7, 6CA7, 6C4, 5U4, 6550, 6L6, and a number of others, are desirable. Others are a drug on the market, although the radio folks need some not on the above short list also.
 
Leigh could be right on the basing. I might be thinking of the schematics. One was always backward of the other. Don't throw out the old number series like 26, 27, 80, 43 and such. I just got done repairing a Tektronix 4 channel plug in that I needed 6CL6's for.

The old tubes are worthless unless you happen to be working some old equipment. How many of you have worked on the loctal base tubes and vibrators used in car radios?

Tom
 
The old tubes are worthless unless you happen to be working some old equipment.
That's why I recommended the AntiqueRadios.com site.
Those folks work on nothing but old radios.

How many of you have worked on the loctal base tubes and vibrators used in car radios?
I've serviced many of both, although I usually only work on pre-1930 radios.

- Leigh
 
Best bet for selling is to make a list, with quantities. Hardcore audio guys will not only test, but match/audition for similar performance. There are certain OEMs, like Telefunken, that are more highly prized. TV guys will be looking for specifics or rare ones, as the others are a dime-a-dozen. I'm looking for one "special" one from a combo radio/record player from the 40s. It's special because the marking is gone and I haven't dug out a schematic, so I don't know what it's supposed to be. Ugh.

I have just enough tube stuff to make a tester handy. Got one for about $60 on craigslist last year, and it included the tube chart to sort out the settings.

Chip
 
The short story is that there is essentially NO way for you to determine goodness without test equipment.

I am an old fossil and can design tube circuits, etc. I would not try to hook up some sort of tester, which is why I have 2 commercial ones.

Do as suggested and move them on to someone who wants to take on the job.

Yes, 12AX7, 12AU7, 12AT7, 6CA7, 6C4, 5U4, 6550, 6L6, and a number of others, are desirable. Others are a drug on the market, although the radio folks need some not on the above short list also.

Michael Marx wanted me to make a tester for transmitting tubes until he heard what the tariff would be. Mike would probably buy your tubes, although he would not give you a lot for them. You can find him as SND Tubes, derived from his ham call WB0SND. The glass audio types are a large part of his business so he has to be nice to them, but they drive him crazy. They aren't happy with a good 12AX7, it has to have black plates with a certain sized getter and only certain brands, which is especially funny because manufacturers would trade tubes. They would set up for certain types and swap them for ones they didn't make, so there is no telling who actually made them.

An unrehearsed shot of a corner of my living room. The dark object at the top is an African communications drum, probably a South Congo chief's drum. The large water cooled tube directly below it came fro a transmitter at Rocky Point, NY. Below that is one of the tubes used in the British Chain Home radar system.

Bill

IMG_2839.jpg
 
See if there is an electronic salvage store in th earea. I am in Colorado Springs and the local electronic salvage store has a tube tester.
 
I made a list of them and think I will sell them on E blay and see what happens. i have a bunch of fuses on there now. I get these deals from time to time from local online or in person auctions .Im a sucker for them...Last night I looked the value or what folks are selling them for on bay. I think i will sell them in 3 batches ..as is..for 1/4 of the prices the others are selling them for. Some numbers are: 3BA6, 6DJB, 3DT6, 6DR7, 6EA8, etc...have about 19 different numbers and a total of 88 tubes. You guys are a great help. I just want to sell them. I was thinking as I opened some of the boxes, they look new, because the boxes haven't been opened before. When I open them these old boxes get torn a little, so I hate to open them.
Have to see if anyone wants them. For example I saw a 3BA6 selling for 2.69 and I'm thinking 50 cents each as is. here are 4 3DT6's sellin for 32.50...I was thinking 10.00 each. what a deal...lol...Thanks. Rich
 
Done those.

Also 'acorns', 'peanuts', Dekatrons, Klystrons, and Traveling Wave Tubes. Cavity magnetrons are a different sort of critter, but also on my list.

And if 'unit count' of vacuum tubes matters?
Mcguire AFB. Summer of 1965. Cross-trained on Semi Automatic Ground Environment, NYADS AN/FSQ-7.

My 'regular' mount was AN/GSA-51, BUIC II, 680th RADRON, Palermo, NJ.
Modern stuff. 'Transistors'. Didn't need 3 Mega Watts of power, nor a man-made lake for cooling. SAGE surely did.

AN/GSA-51 was also the first-ever dual-CPU 'puter, (SAGE just alternated its two IBM Whirlwind II). Moreover could have either CPU switched-out and replaced on-the-fly while still managing the Air Battle.

Never touched it, but IIRC, SAGE BOADS was actually slightly larger and a wee wee bit more capable among around 26 or so of the monsters. Closer to Lincoln Labs, so got more TLC from the Gurus with their experiments.

You didn't really think there were only teen-agers in the room did you?

:)

Bill

You are a young squirt. I spent 1966 at Adair AFB, Corvallis, Or after receiving my Master's. Grade E2. I will always remember the 'Q7, one of a kind. Programmed it in Coseal.

Most people will have little use for the tubes you quoted, that stuff is all microwave except for the Dekatraons. Peanut tubes to me were the 7 and 9 pin miniatures, like a 6J6. If you want specials, don't forget the Williams Memory tubes.

Tom
 
This thread makes me feel old. I remember being able to walk into the local radioshack and they would test for you and had drawers full of tubes. I wonder who got all of those old testers. ... and the left over tubes for that matter. Willing to bet most hit the dumpster.

JR
 
I am working on an amateur radio transceiver (Drake TR-4) as we speak. It is from the mid 1950s (Civil Defense era) and has been unused for a considerable period of time. All I know for sure now is that all the tube light up and get warm. No sound from the speaker but many of the RF circuits seem to be operating somewhat. With headphones I can hear background noise.

Bob
WB8NQW
 








 
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