Hickock 533A 12AX7 testing questions

[Dswankey]

I have a coupe of questions and I'm hoping some Hickok owners can get me sorted out as to what I'm doing.

When testing a 12AX7 for mutual conductance am I correct that the Micromhos switch should be set at 3000? (as seen in the first pic)

Per the roll sheet the "Mut. Cond" setting is 1250, is that a max reading? if the meter arrow goes beyond that am I doing something wrong? (as seen in the 2nd pic)




Looking forward to the knowledge that is forthcoming

 

[zackthedog]

Nothing wrong there. 1250 is the "average" new tube rating. Yours may measure higher (or even lower) and still be perfectly fine. Bob Putnak's old blog is an excellent resource on the do's and don'ts of tube testers.

https://tubesound.com/tube-testing-how-to-use-a-tube-tester/#more-743

 

[Catmanboo]

If it says 1250, yes set mu switch at 3000, since that figure is below 3000. If your spec mu is over 3000, set at 6000. On 533a's, supposedly they read ax7's conseratively. You can pretty much tell a good one from a dud though. I recently ran a couple handfuls of ax7's, found one that wouldn't even move the needle on English setting, but it lit up. So, I crank filament voltage up until she blows!

 

[Dswankey]

Thanks to all for the replies

 

[Dswankey]

Gonna clean up the pins on a bunch of 12AX7's and get to testing this weekend.

 

[larryderouin]

I was taught as a kid to interpret it (Hickok roll chart mHos level) as the Minimum good (normal) reading. I've found that over the years that Hickok's measure 12xx7's mHos somewhat low anyway. More important to me is fairly equal sections, even down to 800-900 or so mhos. Below that and most of them higher levels of distortion. Set the switch to the next highest reading vs. the mHos level. If the tube reads higher or close to the set level on the switch, swith it to the next higher level (6000). Have fun.

 

[Dswankey]

Another question I have is should I test a tube after it has warmed up a bit or does that matter?

 

[zackthedog]

Another question I have is should I test a tube after it has warmed up a bit or does that matter?

Definitely warm it up for a few minutes.

 

[larryderouin]

Most tubes will heat up and stabilize within a minute. Use you're own judgement on it, as you'll get as many different answers as members answering.