[time-nuts] Distribution amp - Use a video amp unit ?

ALAN MELIA alan.melia at btinternet.com
Mon Mar 26 17:22:49 UTC 2012


I dont think so, pure quartz melts at, I think, 1440C but glasses (like lead-glass) melt at much lower temperatures 500 to 600C. Remember the chemical glass-blowing skill of the technicians. 

The glass mix has to be formulated to match the expansion rate of the lead seals. A iron alloy with a small expansion coeff. whose name I dont recall was used for the leads. Glasses soften well below melting temperature (I remember "sucked in" 807 and 6146 tubes that had dissipated a few watts to many) Then the softened glass is "rolled" onto the lead. If you look carefully at some glass wire-ended diodes you will see a slight waist where this happened. The seal and adhesion is a thin metal/oxide/glass interface. Soldering temps rarely cause trouble but bending the lead wire close to the glass should be avoided. I used an oxy-hydrogen flame micro-welder for making connections for high temp life tests, so the wires got quite hot, but not close to the metal-glass seal. I only had peripheral knowledge of glass technology but most of the technology was developed in the lamp and valve (tube ) industries. I guess there are great references in the web now :-))

Alan G3NYK

--- On Mon, 26/3/12, Chuck Harris <cfharris at erols.com> wrote:

> From: Chuck Harris <cfharris at erols.com>
> Subject: Re: [time-nuts] Distribution amp - Use a video amp unit ?
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Date: Monday, 26 March, 2012, 15:10
> Yes, but....
> 
> The glass used to make the body of the diode melts at
> something like 1500C!
> 
> -Chuck Harris
> 
> ALAN MELIA wrote:
> > Si juctions are formed at temps of 1000C or more.
> Thermal failure is more likely
> > to be due to alloying of metal contact areas. I used to
> lifetest transistors up to
> > 360C for 20 hours with power applied!! and anything up
> to 6 months at 200C. You
> > cant get those temps with plastic encalsulations though
> glass (double dummet)
> > diodes will stand 300C easily
> >
> > Alan G3NYK
> 
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