[Milsurplus] 2X2 question

[Scott Johnson]

It has probably become gassy, or more correctly, is at atmosphere from a 
breached glass-to-metal seal. The nbright blue is the classic nitrogen 
discharge color, which is what 80% of our atmosphere consists.

Scott
----- Original Message ----- 
From: "Sean Barton" <sean_ee02 at hotmail.com>
To: <scr287 at sbcglobal.net>; <milsurplus at mailman.qth.net>
Sent: Friday, April 07, 2006 4:05 AM
Subject: RE: [Milsurplus] 2X2 question


> Jack,
>
> A blue glow is an indication of a gassy tube.  Air has somehow gotten into 
> the tube and is being ionized at the high voltage, causing the blue glow. 
> Replace the tube.
>
> Sean
>
> ----Original Message Follows----
> From: Jack Antonio <scr287 at sbcglobal.net>
> To: boatandhors at mailman.qth.net, milsurplus at mailman.qth.net
> Subject: [Milsurplus] 2X2 question
> Date: Thu, 06 Apr 2006 22:36:30 -0700
>
> Hi all
>
> Recently I've been working on a WWII countermeasures
> receiver, that uses a 5" scope for display, sort of
> an early "spectrum analyzer". And it was starting
> to work, the scope had a nice bright sharp trace,
> and the signal circuits were working, but needed
> a little troubleshooting to solve a calibration
> problem.
>
> High voltage for the scope tube is generated by about
> 1250 VAC delivered to the cathode of a 2X2 rectifier,
> about -1500 taken from the anode.
>
> After a disassembly/re-assembly trying to troubleshoot
> the IF, when I fired it up, the 2X2 glowed bright blue and
> the line fuse instantly blew. Of course I thought it was
> something I did in the re-assembly, and spent a couple
> of days getting nowhere. Then I pulled the 2X2 plate cap and
> applied -1100 VDC from an external supply  to the circuit with no 
> problems(thinking a capacitor was breaking down).
>
> Then I put the -1100 on the plate cap of the tube, and
> the tube drew lots of current, and glowed a nice blue.
> (No filament voltage)
>
> I pulled the tube and put a variable DC supply across the
> tube, reverse biased, and the tube breaks down at about 290 volts,
> at that voltage it has a nice blue glow inside, the higher the voltage,
> the more intense the glow. The manual says it should withstand 12500.
>
> My question is, anyone have an idea of what the failure mode is?
> (I have some replacement 2X2s coming).
>
> TIA
>
> Jack
>
> Jack Antonio WA7DIA
> scr287 at sbcglobal.net
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