[R-390] Tube Tester

[Drew Papanek]

Bob Camp wrote:

>Is there any interest in a "R-390A only" tube tester? As far as i can
>see you could make one with a handful of parts that would test all the
>tubes in the R390A except the rectifiers. It should do as good a job as
>a TV-7 on the R390A tubes.

Go to    members.aol.com/sbench101  and you will find among other tube 
projects a design for a homebrew tube tester.  It is a transconductance 
tester and incorporates adjustable DC power supplies to operate the tube 
under test  at the same voltages used in an actual application.

It was primarily intended to characterize tubes to apply them in audio 
amplifiers but will test our R-390x tubes.   For the type of test we would 
like to do some features could be easily added:  grid emission, shorts, gas, 
"life test".

An adjustable constant current source in the cathode lead is used to set the 
tube current; that could be removed and the circuit simplified by grounding 
the cathode and using a bias pot in the grid circuit instead.  (Caveat: 
makes it easier to over dissipate on small tubes.)

The unit could be simplified also by removing the sockets intended for 
audiophile type tubes, removing facility for testing pentodes as triodes, 
removing triode mu testing capability.  The power 
transformer/rectifier/filter could be eliminated and power "borrowed" from 
the R-390x by means of a tube socket plug or clip leads (fuse protected, of 
course).

The aforementioned site has settings/ readings for testing many tube types; 
more can be found at another audiophile site:  triodeel.com

Drew

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