[Milsurplus] VT-191 for Homebrew?

[Michael Hanz]

I think he was referring to that particular tube type - the VT-191, 
Jim..._not_ the vast majority of tubes manufactured during the war.  I 
take "Gone gassy" as his catchall for contamination from elements within 
or leakage of the vacuum through faulty seals.  They don't work so good 
at atmospheric pressure. :-)  His experience mirrors mine with an NOS 
batch that I found at a hamfest years ago. All except a couple of good 
ones went to friends who admired the shape.  I rather expect that the 
ones I kept have become contaminated through the seals as well - need to 
check them again when I have some spare time.

IIRC, there were several other specific tube types that had seal 
problems during the war - perhaps others might remember the type 
numbers.  I know that the early AN/APT-4 jammer split anode magnetron 
tubes only had an average documented life of about 30 hours before the 
seals began leaking.  They eventually got the reliability up to around 
300 hours, but that's not very impressive either.  Replacement was 
simply considered part of the cost of doing business.

  - Mike  KC4TOS

On 3/9/2017 10:54 AM, antqradio at sbcglobal.net wrote:
> Really Dave?  The tube making art is so shoddy that well over half of 
> the tubes produced go to gas?  This doesn't square with my experience.
>
> I just finished testing several large boxes of used tubes and found 
> that only about 10% didn't meet minimum performance or were special 
> purpose TV tubes like HV rectifiers or damper diodes.  Only about 1% 
> of those tested were outright dead.  Didn't see any difference due to 
> age as big pin, octal, 7, and 9 pine tubes didn't appear to fail in 
> larger numbers then any other.  Didn't bother to test compactrons 
> since they are, for the most part, special purpose TV tubes.
>
> I think the Tube Collector's Association has well over 400 members and 
> perhaps there are several times that in tube collectors who are not 
> members so I hope that the McDonalds are much larger in Texas!
> Regards,
> Jim
>
> ------------------------------------------------------------------------
> *From:* David Stinson <arc5 at ix.netcom.com>
> *To:* milsurplus at mailman.qth.net
> *Sent:* Thursday, March 9, 2017 6:26 AM
> *Subject:* [Milsurplus] VT-191 for Homebrew?
>
> While it's a cool-looking tube and all (UFO!),
> I'd hesitate to build a transmitter for it.
> The majority of those tubes have gone gassy.
> I've seen many NOS in the box and exactly
> *two* that still had intact seals.  I'd suspect that
> once a "good" one was placed in service with
> all the heat it generates, the flawed pin seals
> will let go on them as well.
>
> But then- it's not like we're talking about the
> Mona Lisa here.  If you gathered every person
> who still cares about preserving these tubes in
> the entire world to lunch, you probably could
> get them all in the local McDonalds.  So maybe
> it would be worthwhile just for your personal
> joy and satisfaction.  If not used for something
> like this, their inevitable fate is to sit in a box
> until their trip to the landfill.
> One man's opinion....
>
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