[Amps] Glass Vs Ceramic

[Roger (K8RI)]

In my opinion and I have worked with glass, quartz, and metal using H2 
torches, but not sealing tubes. Sealing glass to metal has remained as 
much an art as science.
I think the results of companies being sold (bought out) and the same 
tubes (those with good seals become bad) with new people doing the 
joining might be an indication.

The area of the seal Vs the thickness of the seal "seems" to play a 
part. Small tubes with small pins and a thick base (compared to the size 
of the pins) seldom seem to have problems

External anode tubes with ceramic insulation can heat the sealing area 
hot enough to silver solder the ceramic to the metal. The silver solder 
bonds to to both materials.

Thoughts?

73, Roger (K8RI)


On 6/6/2017 Tuesday 12:05 PM, Chris Hays wrote:
> One should always be careful of generalizations.  Its all about the seals!
> While the 3-500Z indeed has a reputation for being a "leaker," you also find
> anecdotes about tubes that have been on the shelf since the 40's coming up
> just fine. Caveat: its always a good idea to bring them up slowly!
>
> Indeed, small receiving types very rarely leak.  Of course they generally
> don't have kilovolts of plate voltage, which might contribute to this
> reputation.
>
> A couple of anecdotes from my life as a broadcast engineer.
>
> When I started working at KRLA (AM)in the 70's, they had the two oldest
> transmitters in the market.  One of them was a truly amazing 10kw Western
> Electric. It had a pair of big water-cooled glass triodes for the final (it
> was a Doherty configuration). We had these tubes rebuilt over and over again
> by Cal Tube Labs and they were fine.  Then all of a sudden, they wouldn't
> hold vacuum and would arc after being shut down for a mere 12 hours or so
> (the transmitter was a backup that was run in the over-night period or if
> the main failed).  To make a long story short, it turns out that the fellow
> that had been rebuilding these at Cal Tube Labs died, and apparently took
> some knowledge with him.  That spelled the end of life for that transmitter.
>
>
> The other transmitter was a 1950's Continental 317. The driver section had a
> pair of Machlett 5531 external anode glass triodes. By the time I arrived,
> these tubes only had about 1500 good hours.  They also would arc once at
> initial turn on.  According to the supervisor (Tom Weatherall - SK), the
> problem with the tubes started when, as part of an anti-trust settlement,
> Western Electric had to divest all its broadcast interests.  Their tube
> division was Machlett labs, which was sold to Raytheon. They couldn't build
> a clean 5531 tube after that change. Unfortunately, the elaborate glass
> design meant nobody wanted to attempt to open the tubes for a rebuild.
>
> While ceramic tubes appear to held vacuum better, it probably has more to do
> with the manufacturing knowledge and skill set for the seals.
>
> Chris, AB6QK
>
> ORIGINAL MESSAGE:
>
> Message: 5
> Date: Tue, 6 Jun 2017 15:14:26 +0000 (UTC)
> From: Catherine James <catherine.james at att.net>
> To: Amps group <amps at contesting.com>, 	Kimberly Elmore
> 	<cw_de_n5op at sbcglobal.net>
> Subject: Re: [Amps] 3-500Z cool down time
> Message-ID: <1744412737.2823165.1496762066255 at mail.yahoo.com>
> Content-Type: text/plain; charset=UTF-8
>
> Kim,
>
>     It's generally recognized that glass tubes have poor shelf life due to
> slow leakage.  I have heard many reports of this from people I trust.
>
>     They will last much longer if the plate gets hot at least a few times a
> year so that any leakage can be gettered away.  For tubes in regular use
> rather than on the shelf, it doesn't seem to be a problem, but it makes it
> difficult to stock up with spares.  Many amateur users rotate their shelf
> stock into the amp at least once a year.
>
>    Is the 3-500Z used much outside of ham radio today?  If so, who are the
> primary users?
>
> 73,
> Cathy
> N5WVR
>
> --------------------------------------------
>
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