I bought a IT21 tube tester on craigslist and am having problems and hope someone can help.
The unit powers up and the set line switch works, the meter gets to the middle of the dial and everything seems fine to that point.
When I insert a tube, set the switches and then use the test switch the meter always pegs all the way (good or bad) never a reading in the dial mid range.
I opened the unit and found an additional resistor wired in parallel to the 75k ohm resistor. The additional resistor was around 500k ohms. It isn't in any documentation I can find.
I removed the extra resistor but the meter still pegs when testing a tube. I checked all resistors in the unit and they all test OK but
when I teak a reading across the 75k resistor I get a reading of around 1000 ohms. I take a lead out of the circuit and the resistor is 75k ohms.
If someone has an IT21 and can do a check of the 75k ohm resistor and let me know what it reads in circuit on their unit I would really appreciate it.
I looked and do not see any parallel circuit in the tester that would bring the value down and I don't see any mis-wiring in that area of the tester.
Thanks for any replies.
Jim
The unit powers up and the set line switch works, the meter gets to the middle of the dial and everything seems fine to that point.
When I insert a tube, set the switches and then use the test switch the meter always pegs all the way (good or bad) never a reading in the dial mid range.
I opened the unit and found an additional resistor wired in parallel to the 75k ohm resistor. The additional resistor was around 500k ohms. It isn't in any documentation I can find.
I removed the extra resistor but the meter still pegs when testing a tube. I checked all resistors in the unit and they all test OK but
when I teak a reading across the 75k resistor I get a reading of around 1000 ohms. I take a lead out of the circuit and the resistor is 75k ohms.
If someone has an IT21 and can do a check of the 75k ohm resistor and let me know what it reads in circuit on their unit I would really appreciate it.
I looked and do not see any parallel circuit in the tester that would bring the value down and I don't see any mis-wiring in that area of the tester.
Thanks for any replies.
Jim