[Boatanchors] TUBE TEST

[Jim Wilhite]

The tester I have is a Hickok disguised as a Western Electric and it 
allows me to lock the test button down.  With it locked in the test 
position I adjust the line voltage to compensate for the drop. 
Another feature it has is a toggle switch marked Normal and Test.

According to the manual you read the meter in the Normal position 
then move the switch to the Test position.  If the reading drops 
more than 10% the emission of the tube is low and not long for this 
world.  Replace at your option.

I, too, was in the 2 way business at the end of the tube era and 
chose to do as you describe.  If it dropped too much then it was 
replaced.  A tube was cheaper than a second service call to replace 
the tube anyway.  Many people don't like tube testers because they 
say the tester is not accurate and gives a false impression about 
the tube.

I believe they are like an EKG, just a snapshot at the moment.  I 
always left the tube with the Test button pressed for a while to see 
what the tube did when it warmed a considerable amount, so I had 
good luck with a tester.  It did prevent me from prematurely 
replacing quite a few tubes, which is important if you want to make 
a profit.

Jim/W5JO


----- Original Message ----- 
> Having done maintenance years ago on commercial two-way gear 
> (6146s, etc) you
> have to consider that when you push the "test" button and the big 
> tube draws
> plate current, the input line voltage drops a tad. (evidenced by 
> the drop at
> the AC "cal" point, the first setting prior to testing the tube.) 
> This causes
> a small drop in filament voltage.  A weaker tube that has many 
> hours on its
> filament will show a drop in emission and consequently a drop in 
> plate current.
> Cathode type tubes also suffered from a progressive condition 
> called, "cathode
> interface."  This does not mean it won't provide high output under
> normal voltage
> conditions, but that its capability to do so will drop off sooner 
> than later.
>
> A new tube will sustain a small drop in filament voltage without 
> losing
> detectable emission.
>
> This used to be the test for "replace" or "don't replace."  To cut 
> down on
> future "trouble calls" we usually replaced the ones showing drop 
> off.
> I was always appreciative of this particular test.  A test that 
> Hickok never
> planned, no doubt.
>
> If any NEW tube suffers this way it must be a manufacturing
> problem.  What else?
>
> Perry   w8au