Tube tester / measuring device

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beatnik

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Joined
Oct 18, 2009
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I am jumping into some tube projects and acquired a decent stock of nos tubes

Would like to buy a measurement machine to test the tubes and select / match them for stereo units

I have seen some devices, especially on ebay, but because lacking knowledge, I still don't know what parameters of the tubes are important to measure, thus I don't know which kind of machine I should be looking for

Would really like to hear your recommendations on this one

Thanks !
 
What types of tubes, primarily?  This is something of a sensitive subject as people tend to trust their testers but I feel that most are not very useful for matching.  So much that I'd recommend just testing the circuit with the tubes in use rather than spending a few hundred on a tester that may or may not be giving you results that are relevant to your circuit.  Since you say your tubes are NOS (not used), that's good because determining health/remaining life is another thing most testers are poor at (they're usually far too generous). If I had to use one mid-priced tester for popular 9-pin signal tubes I might go with a TV7 as they are usually reasonable when it comes to12A_7s and such.  If you don't have a lot, I'd send them to someone to get tested on an Amplitrex.  Of all the testers I've used, that's the only one I trust enough to rely on for my business.  Noise testing is another thing entirely, but I'm assuming you will just do that on your equipment.
 
I use an AVO MkIV, but was lucky enough to get it for almost free.
I don't know the second hand value in Britain, but I believe they're expensive over there too.
Might get lucky.

There are lots and lots of testers around that won't give you the possibility to actually measure/get readings of  tube transconductance (sensitivity), which is the essential parameter.

Tip: Google tube testers and mA/V
 
Bowie said:
I'd recommend just testing the circuit with the tubes in use rather than spending a few hundred on a tester that may or may not be giving you results that are relevant to your circuit.

this is actually the best advice, but i will keep an eye open for the models you recommended

thanks !

 
If you are ready to spend some money, take a look at http://www.amplitrex.com/
PS: L3-3 is my choice.
 
I think matching tubes in the specific circuit is the best.
I have a Hickok tube tester, it measures transconductance, and when I built a guitar amp and put in the output tubes that had same transconductance, they had very different anode current. I was able to pick a pair of tubes with similar anode current afterwards.
 
+1

I use a tester (AVO MK4) for general Go/NoGo, and then in-circuit measurement for matching the needed parameters.

But then I'm much more dependent on good matching than most others, as I mainly build stereo-tracking devices with little or no feedback.

Jakob E.
 
yeah a basic tester would be useful to avoid at least putting dead tubes in the circuit

which tools you use the most for stereo matching measurements on tube circuits ? multimeter, oscilloscope, dB meter,.... ?
 
ungifted said:
If you are ready to spend some money, take a look at http://www.amplitrex.com/
PS: L3-3 is my choice.

+1 for  L3-3 (or L1-3).
Measured thousands of different tubes.
Very flexible and informative device.
 
If you have an amp that is going to use your tubes, and you have multiple of the same tube to mix/match, then I also recommend using the amp as the tester - especially if it has fixed bias adjustment of each side of output stage (assuming PP).

What you can test for depends on the tube you are rolling.  For example:

- use a variac to confirm the tube is operating nominally at a reduced voltage prior to any damage being caused.

- use a voltmeter to compare bias settings of preamp stages.

- if an output tube, then use a voltmeter to set nominal output stage bias current (to optimise low frequency response of OT).

- use a PC based spectrum analyser like REW to observe the amplifier output, or the output of a preamp stage (depending on the tubes being assessed).  Distortion level is one metric to use.  Hum level can be used to identify poor heater-cathode performance.  Apply a calibrated 'clang' to the chassis or tube to compare microphonic output.  If there is no global feedback, then output signal level may indicate changes in stage gain.
 

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