Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: RCA Vacuum Tube Arcania  (Read 4528 times)
KF7Z
Member

Posts: 36




Ignore
« on: May 01, 2013, 08:51:31 AM »

There is an RCA 6293 vacuum tube now being offered for sale on Ebay as "New Old Stock" for $40, which would be a very attractive price.  However, for those of you who might not know it, there is a clear indication in the photo that could lead one to believe that this tube is misrepresented as being NOS.  That is, the RCA logo and tube ID are visible in the photo as being a muddy gray color. 

Many decades ago, as a teenager, I worked at an electronics supply house where the largest single category of sales were RCA vacuum tubes to radio and TV repair shops.  We would ship out many hundreds of RCA tubes every day to shops around the state. The General Manager of our store told us that the ink that RCA used at that time (the era of the modern red and white box, and the slightly early red, white and black box era) was of a special formula that changed color when the tube was heated to operating temperature.  The ink on a new tube started out as a reddish orange color, but would turn to a muddy gray color after the tube had been heated.  We used this indicator as the basis for accepting or declining "un-needed" tubes for return.  (The date code determined warranty replacement in the case of early tube failure.)

On this basis, it is easy to conclude that the 6293 tube now being offered on Ebay as "New Old Stock" is misrepresented.  I understand that it is not a shocking conclusion that an Ebay item is misrepresented.  I just offer this bit of tube lore for those who might not be aware of it, as a way to judge other claims regarding RCA tubes.

We only sold RCA and a few Amperex tubes.  Does anyone know if any of the other tube manufacturers used ink of this color-change nature, or does anyone know when it was that RCA started this practice?

Best to all,
John K7KEY (ex-KF7Z)
Logged
N2EY
Member

Posts: 3894




Ignore
« Reply #1 on: May 02, 2013, 11:03:08 AM »

How long would it take for the color change to happen?

Could normal testing in a tube tester do it? How about storage in a non-climate controlled place - say, an attic where it gets over 130 degrees in the summer?

73 de Jim, N2EY
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #2 on: May 02, 2013, 11:21:00 AM »

Also, there can be the possibility of chemical aging/decomposition of the substance over time, as well. 

Of course, caveat emptor should always apply to any purchase.


73
Logged
N3QE
Member

Posts: 2287




Ignore
« Reply #3 on: May 02, 2013, 11:37:25 AM »

I've gone through both "new old stock" and "old used" RCA 6146's and never saw any color-changing ink.

Red labels were used on some tubes (RCA and others) but they stayed red. Some audiophiles distinguish based on label ink and base color but I don't understand the implications.

If we want to talk about ink colors... I always liked the green that GE and Sylvania used towards the end. Far easier for me to read than anything else.
« Last Edit: May 02, 2013, 12:31:30 PM by N3QE » Logged
KF7Z
Member

Posts: 36




Ignore
« Reply #4 on: May 02, 2013, 01:09:08 PM »

I've gone through both "new old stock" and "old used" RCA 6146's and never saw any color-changing ink.

I have seen hundreds of fresh RCA tubes with red print.  I have seen hundreds of used RCA tubes with gray print.  None of that is proof, but does lend support.

Since there probably isn't any of this ink on RCA tubes that is less than many decades old, it is quite possible that the ink additive that caused the color change is no longer reactive to heat.  In the day, most tubes would sit on a dealer shelf for no more than a few months.  The color change matter was only relevant for a few years after manufacture, when the dealer might benefit from knowing if the tube being presented for return had been used.  If the date code revealed that the tube was several years old, that would influence the decision to accept the return, regardless of ink color.  This whole matter was a consideration of the old retailing environment when the shade-tree Radio and TV repairman could buy a handful of new tubes, sub them out one at a time, and return the ones that didn't affect the problem.  Or try to return the used tube in the new box.  It was a simple retailing precaution by the manufacturer.

There was surely a specification for the time/temperature curve that induced the chemical reaction, and it was probably carefully specified, but who knows where to find that information now?  The was surely also a specification for shelf-life stability of the ink.  Both are probably deep in RCA archives now.

Anyway, the information might be useful to someone thinking of buying a expensive old tube that is represented as unused.  Red print might not guarantee unused, for the above reason.  But the muddy gray ink might still be revealing.
« Last Edit: May 02, 2013, 01:21:13 PM by KF7Z » Logged
KF7Z
Member

Posts: 36




Ignore
« Reply #5 on: May 02, 2013, 02:12:10 PM »

Or maybe this is a worthless bit of arcania - decades after the fact.
Logged
K8AC
Member

Posts: 1477




Ignore
« Reply #6 on: May 02, 2013, 05:18:18 PM »

Interesting theory about the color of the lettering, but - I've been using tubes for the past 50+ years, many of them RCA, and those that had the orange lettering still do and those that had grey lettering out of the box still do.  Some of the tubes have been in service for decades.  It may be that some specific tubes had labeling that would change when heated, but none that I ever ran into.

73, K8AC
Logged
KD0REQ
Member

Posts: 971




Ignore
« Reply #7 on: May 03, 2013, 08:58:15 AM »

didn't Amperex orange fade away on hard usage, too?
Logged
KF7Z
Member

Posts: 36




Ignore
« Reply #8 on: May 03, 2013, 11:28:48 AM »

Interesting theory about the color of the lettering, but - .

Nothing else that I can add, but that the friend who informed me of this, the manager of the facility, S.K. Hank Leaders W7BDU, was a brilliant and very respected ham with a lifetime in the industry.
Logged
N2EY
Member

Posts: 3894




Ignore
« Reply #9 on: May 03, 2013, 02:41:30 PM »

The color-changing-ink story may or may not be true. I've heard a lot of tube stories but never that one.

But IMHO, even if true, it just doesn't matter any more.

Most of the US-made tubes you see on sale today are decades old. (There are a few exceptions, of course). Many types were made over a very long period of time by a wide variety of manufacturers.

If they really did use a color-changing ink, there's no way to know for sure that it would retain the color-change feature for decades. Particularly if stored in hot, cold, and/or humid locations.

Maybe the ink changes color all by itself over time. Maybe it doesn't.

The only way to know for sure if a vintage tube is still any good is to test it.

73 de Jim, N2EY
Logged
N3QE
Member

Posts: 2287




Ignore
« Reply #10 on: May 04, 2013, 08:47:10 AM »

Went and looked at a mix of new and used RCA tubes I have in the red-and-white box era.

For GLASS tubes:

Most of the new miniature tubes I have came in a sleeve of ten and I have no suspicion they are washed, I am sure they are genuine new tubes.

The most common new tube, had red RCA logo, along with grey tube number.

The most common used tube, had red RCA logo, along with the grey tube number.

I found many RCA 6146(A,B)'s both NIB and in use in rigs for decades. They all have silver tube number on the glass, and black RCA logo on the metal base. I would guess that the transmitter tube in your original post would be very very similar in manufacturing to the 6146's.

The new not-miniature not-6146-number RCA glass tubes I have came in original JAN boxes. I have a particularly large stock of 807's and I might assume these receive the same attention paid to other transmitter tubes like the one mentioned in your original post.

The new RCA JAN 807's I have, have no red RCA ink on them, just the tube number on the glass, and the JAN markings on the base.

The used RCA 807's I have, have no red RCA ink on them, just the grey tube number on the glass, and the JAN markings on the base.

For METAL TUBES:

New RCA metal tubes (esp 6AC7 which for some reason I have a very large stock of) have red RCA logo and red tube number. These are in early 70's era red-and-white-rectangle boxes. I stuck one in the tube tester for a few days with filament voltage on it, and the ink color did not change at all.

Old RCA metal tubes found in radios around the house (in use for decades ), have red RCA logo and red tube number.
Logged
KE6EE
Member

Posts: 398




Ignore
« Reply #11 on: May 04, 2013, 12:47:39 PM »

Went and looked at a mix of new and used RCA tubes I have in the red-and-white box era.
For GLASS tubes:
Most of the new miniature tubes I have came in a sleeve of ten and I have no suspicion they are washed, I am sure they are genuine new tubes...

Nothing, but nothing, beats real evidence, well-documented. I think it's called science.
Logged
AC5UP
Member

Posts: 3893




Ignore
« Reply #12 on: May 04, 2013, 04:49:25 PM »

I've been playing with tube gear for nearly 50 years and this is the first I've ever heard anything like this....... Not saying it wasn't possible in some special application or that I've heard it all, just sayin' I have my doubts. Many tubes turn slightly grey inside the glass as they age and some, like the 6CB6, had a smoky grey band inside the middle of the envelope when new. The closest I can recall of an ink changing color was due to heat fade and that was obvious as the middle of the tube would be more faded than the top or bottom.

BTW:  RCA changed logo's every 20 years or so and they used white, grey or red ink on their glass tubes depending on the decade. Some of the metal tubes that N4NYY doesn't like were silver on black and looked good, in an industrial chic kinda' way..................  Roll Eyes
Logged

Never change a password on a Friday                
K1DA
Member

Posts: 513




Ignore
« Reply #13 on: May 06, 2013, 09:54:53 AM »

Tube companies regularly made tubes for each other, Raytheon being a prime example, and I doubt there was a special ink involved.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!