Testing Ck5703 tubes

[Zero Cool]

Anyone have any info on testing micro sized CK5703 tubes as used in the Musical Fidelity Tri Vista 21 DAC?? one tube has lost vacuum and im not sure if the others are any good.

I have access to a Hickok 539B and a Amplitrex. have not looked to see if the amplitrex has settings in it or not yet. I would need to make an adapter in any case i guess.


Zc

[wa2ise]

If that tester is at all similar to a TV7D/U (from a few pictures googled off the web, it does look similar except a different layout of the switches and sockets) the settings for a TV7D/U for a 5703 is DU5 1060, heater 6.3v, bias setting 20, range setting D, button to press 3, minimum meter reading is 25.

If a tube loses vacuum, the meter response will be zero, as the tube fails to conduct any current, and usually the heater will not be glowing (the air convects enough heat to cool the heater and cathode so it doesn't get hot enough to emit visible light. And forget about electrons.

These tubes were designed to take a fair amount of physical abuse, the sort you'd get in aircraft and rockets. So if the other tubes light up, they are probably in good shape and thus fine. And if the getters stay silver shiny, and not turn white, that's also a good indication that the vacuum didn't leak out.

There's probably a small crack in the glass envelope (maybe at the leads) that let the vacuum out.

[Zero Cool]

the way these tubes were mounted seems to be the issue. they used rubber grommets which out gas oil over time and the rubber turns hard and brittle. the one tube that lost vacuum did turn white and the glass is cracked under where the grommet sat on the side of the tube. I need to figure out a better mounting system.