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Author Topic: Vacuum tube identification.  (Read 3814 times)
K2OWK
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« on: March 05, 2013, 09:12:11 PM »














Vacuum tube identification.

« on: Today at 09:04:17 PM »


QuoteModifyRemove
 

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I have a strange question. I am restoring a National NC-98 receiver. I guess I pulled a dumb one. I removed all the tubes for cleaning. The placement location is not a problem as I have a diagram, and the sockets in the chassis are all marked. Now for the problem. When I cleaned the old tubes the tube markings came off some of them. Two of the tubes are obvious as the sockets are of a different size. Some of the tubes still have readable markings. Now for the problem three of the tubes that I can not read the markings on have the same size sockets. Is there any way I can tell a tube number or type by looking at it internally? I have the schematic of the receiver so I can identify the use of the tubes, again is there any way to identify the tubes with the numbers that I cleaned off, or do I need to buy new tubes to replace the unknowns?

Any help would be appreciated.

73s

K2OWK
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W0BTU
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« Reply #1 on: March 05, 2013, 09:20:05 PM »

Try breathing on the glass where the numbers were. Before the fog evaporates, you may be able to read it. I've read the faded printing that way many times.
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WD8KNI
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« Reply #2 on: March 05, 2013, 10:43:30 PM »

On tubes that the moisture contained in my breath did not work, I was successful with steam from boiling water..  Fred
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KC9NVP
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« Reply #3 on: March 06, 2013, 10:18:30 AM »

Hate to make your job harder, but you may need to pull out a tube reference book and compare the internal workings, if you can see them to what is in the book.  Sounds like you are down to a couple of tubes and based on the tube number from the schematic, you should be able to identify the missing numbers.   Use the missing numbers to see what the tube book diagrams show.  I have had to do a few tubes that way, more work, but can be done.

David
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WB6BYU
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« Reply #4 on: March 06, 2013, 11:08:53 AM »

With glass tubes one who is experienced with them can often tell the pin connections just
by looking at them.  A dual-triode will usually have two separate sections within the tube,
each with grid, cathode and plate connections.  A pentode or tetrode may be more difficult,
but often you can see which lead goes to the cathode (near the center) and which goes
to the outer elements:  counting the active leads running down to the base will often
provide a good starting point.

Start with some known tubes and examine them closely to see how they are configured
internally, and progress from there.

Of course, with metal tubes, or other cases where you can't see inside, that doesn't help.
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AC5UP
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« Reply #5 on: March 06, 2013, 04:14:19 PM »

...metal tubes often have the tube type stamped into the rim around the base.

Since the metal cover needs to be crimped apparently it's no big thing to emboss the tube type into the rim. For all I know Unca' Sam wanted 'em that way as a safeguard against rust. Wire brush the rim and maybe there's enough left to ident? You'll also find common incandescent lamps typically have the voltage / wattage rating stamped near the top edge of the Edison base.
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W0BTU
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« Reply #6 on: March 06, 2013, 04:38:13 PM »

KC9NVP and WB6BYU said it very well. For an experienced tube man, it is absolutely possible to get the tubes back in the correct sockets in short order, using those techniques.

Try the fog on the glass first. That's much easier. (These aren't metal tubes, are they?)
« Last Edit: March 06, 2013, 04:40:19 PM by W0BTU » Logged

K2OWK
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« Reply #7 on: March 06, 2013, 04:39:41 PM »

Thanks to everyone for your help. I was able to identify 8 of the nine tubes, so now I know where they all go. The cold tube hot breath worked well.

Now if anyone can suggest an easy way to restring a dial, I would appreciate it? I have an excellent dial cord restringing guide, but I am finding it very difficult. Which end do I start with? I am using the original cord which came loose when to tension spring came off, so the original loop ends are there.

Thanks,

K2OWK
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KE3WD
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« Reply #8 on: March 07, 2013, 06:08:17 AM »

I spent time typing a Reply to this thread yesterday and today my reply has disappeared. 

This is not the first time. 

Anyone else experience disappearing posts around here? 
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WA3SKN
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« Reply #9 on: March 07, 2013, 07:50:54 AM »

I was going to suggest re-tubing the radio with new tubes, but looks like the problem has been resolved.  There are ways to test tubes, but it is a pain.
73s.

-Mike.
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N9JFG
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« Reply #10 on: March 07, 2013, 10:14:38 AM »

A technique taught to me 50 years ago was the rub the tube through one's hair - the oil on the hair would oftem make the markings visible -
(Sorry for all those that have lost the possibility of doing this!)

73 John
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KD0REQ
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« Reply #11 on: March 07, 2013, 11:27:24 AM »

KE3WD, I lost a post in this thread, too.  it was not exactly wisdom from God, so I'm not upset.  likely issue is they had a server issue of one type or another... lost it during a resync or backup, VM went down at a hoster shortly after posting and it wasn't out of cache, whatever.

but the upshot was if you can identify one tube of type X, then you can stare and compare to group its kin, but double-check in the tube tester to make sure the pins match up inside.  plenty of AF/RF pentodes look the same but are wired way different.
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K9YLI
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« Reply #12 on: March 09, 2013, 09:15:37 AM »

to all and  sundry..  when  you do identify  a hard to read tube. 
mark it with a  crayon.....  stays for years..

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