[AMRadio] Step Start

D. Chester k4kyv at charter.net
Wed Dec 13 17:01:56 EST 2006

> Problem is that this stuff is not mercury at least not liquid.  There is 
> plenty of that also but I not concerned with that.  It's the flaky stuff 
> clinging to the top inside of the glass that bother me.  It is more like 
> ash but shaped like the anode as though small pieces of it flaked off. 
> There so thin and light that they cling to the glass and no amount of 
> shaking will get them to drop to the bottom and out of the way.

I have had that stuff in MV rectifiers.  If you can't jar it loose from the 
glass, the tube will probably flash over.  At least that's been my 
experience.  I have been able to jar it loose and let it fall to the bottom 
of the tube, and the tube would work properly.  But if you have that stuff 
inside  the tube, the tube is pretty much shot.  I think it is some kind of 
coating or reaction between the mercury and the anode metal, that has flaked 
off the anode.  Its presence anywhwere near the anode-cathode space in the 
tube, even on the glass envelope, will cause flash-over.

Best to get a good tube.

I have also had good results with xenon gas rectifiers.  4B32 replaces 872A, 
and 3B28 replaces 866A.  They are less cantankerous than MV rectifiers, but 
they don't have the pretty blue glow.

Don k4kyv 

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