I just got my B&K 747 tube tester back from professional
calibration and service at CTech Electronics, and I'm now very
careful in how I use it, so as not to damage anything like I
aparently did before.

My question is this: I now hit the 'shorts' button first thing
after the filament is lit. If it lights, I pull the tube and do NOT
hit the 'test' button.

But is there ever a circumstance where a 'good' tube will cause
the shorts light to light? I ask because I had some 6146s a while
ago that would light the 'shorts' light up, but tested far into the
'good' range scale.

Any input would be helpful,

Thanks

Dave WB7AWK

On Tue, 15 Jan 2008 21:26:15 -0800, None wrote:

I just got my B&K 747 tube tester back from professional calibration and
service at CTech Electronics, and I'm now very careful in how I use it,
so as not to damage anything like I aparently did before.

My question is this: I now hit the 'shorts' button first thing after
the filament is lit. If it lights, I pull the tube and do NOT hit the
'test' button.

But is there ever a circumstance where a 'good' tube will cause the
shorts light to light? I ask because I had some 6146s a while ago that
would light the 'shorts' light up, but tested far into the 'good' range
scale.

Any input would be helpful,

Thanks

Dave WB7AWK

On my tube tester there are some settings on some tubes that'll cause a
short indication, but they're listed in the manual (and presumably you
don't do an emission test across those terminals).

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

None wrote:
I just got my B&K 747 tube tester back from professional
calibration and service at CTech Electronics, and I'm now very
careful in how I use it, so as not to damage anything like I
aparently did before.

It is very hard to damage a tube tester... but an interelectrode
short can do the trick. Usually the meters have a diode in parallel
with their movement to limit current to a safe value.

My question is this: I now hit the 'shorts' button first thing
after the filament is lit. If it lights, I pull the tube and do NOT
hit the 'test' button.

That is always a good idea.

But is there ever a circumstance where a 'good' tube will cause
the shorts light to light? I ask because I had some 6146s a while
ago that would light the 'shorts' light up, but tested far into the
'good' range scale.

Yes, many tubes have intentional shorts that can show up on some of
the test positions. They should be mentioned on the tube chart.
If you check your tube tester manual, it may have a table that shows
what the different positions on the shorts switch test for.

For instance, on Hickok, position 1 is heater-cathode shorts...

-Chuck

It is very hard to damage a tube tester... but an interelectrode
short can do the trick. Usually the meters have a diode in parallel
with their movement to limit current to a safe value.

Hi Chuck - I am sure that's what I did. I fried 2 zener diodes in the meter
circuit, and also took out the bias pot (wirewound) in the process, plus of
course blew the internal fuse (soldered in place)
..
I still don't know exactly what I did, but CTech did a great job
repairing and recalibrating it to factory specs so I'm now very careful
to not do stupid stuff again!

Dave

But is there ever a circumstance where a 'good' tube will cause the
shorts light to light? I ask because I had some 6146s a while ago that
would light the 'shorts' light up, but tested far into the 'good' range
scale.

One of the calibration steps in the manual is to set the "shorts"
sensitivity, using a 1 megohm resistor. Power tubes are allowed a
little more leakage than receiving tubes, so could exceed the "shorts"
threshold and still be good.

Alan