[Heathkit] TT1A

[Arthur Shulman]

Peter,
You are seeing a very common problem with many inexpensive tube testers when testing power tubes with heavy current drain.
Simply, the transformer in the tester is undersize for the task when a power tube, or any high current tube, is tested and expected to draw close to its rated current. Poor voltage regulation, usually because of economies in design, allows the filament voltage to drop below normal under load. The solution is to test quickly before the filament (or cathode) has a chance to cool. Just a quick glance at the meter reading for a second or so, is enough. Holding the test condition any longer allows the reduced filament voltage to affect emission.
If you want to study the performance for a longer period, it is indeed necessary to readjust the line voltage control. Just remember to remove the tube immediately after testing, so as to not subject it to increased filament voltage.
Also, service the instrument and make sure all voltages are accurately calibrated according to the manufacturer.

Arthur Shulman VE3ZV

Peter Beka wrote:

> Ok,
> Here is an odd phenomenon I have discovered with this tester.  Being a younger less experienced tube fanatic, maybe a more "experienced" Heath user can solve this for me.  I have a TT1A, and when testing larger octal output tubes ie: KT88's El34's ect., the manual indicates to set the line voltage in the Heater Shorts position let it warm up and then run the tube through the shorts test, then test the tube.  All of my KT88's test low as do EL34's ect.  I measured the AC heater voltage and it indicates that it is 3 volts (too low) and the only way to put it to 6.3 volts is to readjust the line voltage in the "tube test" position .  This gives more accurate tests of my KT88's ect. but is not what the manual indicates.  Can anyone set me straight here on this one?
>
> I have fully restored the  unit with new capacitors, diodes and any out of tolerence resitors.  All tests are good on the "testing" section of the manual and all voltages are correct.  The unit calibrates perfect.
>
> Thanks
>
> Peter
>
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