"BillJ" wrote in message
...
Rich Greenberg wrote:
In article ,
BillJ wrote:
I have Sylvania Electric tube tester. Has worked for
many years, but
today known good tube test flat zero. Filaments do
light. I have no
model number, it is a green panel, with roll chart.

Anybody know what might go wrong. I looked inside and
see one tube, a
1EL7 I think it was. Other wise looks good, with no bad
smells.

Is there a fuse? Is it good?


Yes, fuse in the A.C. line and is good. Turns on with
needle at center and line voltage setting works to put it
right in center. After many years of troubleshooting and
doing restorations, this is the first time I have looked
inside a tube tester. Wow, what a wiring puzzle! I had
never thought about how they work, but guess there is
actually a B+, bias, etc applied as well as filament. Then
is measures gain thru the tube? Somehow?

There are two types of tube testers, those which measure
only filiment emmision and those which measure
transconductance. Most also test for leakage between
elements or gassy tubes. Transconductance or
mutual-conductance (different names for the same thing) have
oscillators in them and measure gain. Most also test
emission.
I am not clear on whether the tester fails with only one
tube or with any tube. If its only one tube, or one type of
tube, the chart settings may be wrong. This is pretty
common. If it fails with any kind of tube the B+ maybe dead.
I can trouble shoot some stuff without a schematic but its a
pain to say the least and you are right about tube testers
being rat's nests of wiring. If you have access to another
tester test the tube in your tester if it has one.




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Richard Knoppow
Los Angeles, CA, USA