872A... or is it?...

[Sparky95]

I have recently purchased two (supposedly) 872a's off ebay. I wanted to make a set of 4 with my 872AX's, though I found they look different. Unfortunately the AX's are hard to come by. Long story short, it looks like an 872a, but I see no mercury droplets, and when heated there's no mercury fog or coating at the top before it's completely hot. They also have a getter, indicating high vacuum? What have I stumbled across?

 

[HollowState]

A picture would sure help, but it might be a 4B32 xenon rectifier.

 

[Sparky95]

The internal structure looks like it, but not the bulb.

 

[HollowState]

Well, the envelope is incidental and may vary somewhat by manufacture.

 

[Sparky95]

True. Unfortunately there is little in the way of markings on the tube. Though judging by the lack of a gap between anode/cathode, the lack of the characteristic bowl shape of mv anodes, and not a speck of mercury in the tubes, I reckon they are indeed 4b32 rectifiers. I hope $20 shipped wasn't a bad price...

 

[hpeter]

wire dc psu , (30-40v and 100mA) and watch the voltage.. heaters on.
if it has gas/hg, it should drop like zener <20v.
adjusting current, gas tubes are more Ufwd constant than vacuum t.
look from bottom for heater and plasma color
xe-dim pink

 

[hpeter]

curve tracing it will show for sure if is gas or vacuum.

 

[Sparky95]

Did the testing. (except curve trace). Definitely Xenon, nice purple glow, but nowhere near as cool a glow as MV.