Hello All,

I have a Hickok 539B which I recently have attempted to calibrate, using the
Daniel Schoo procedure, but using a calibrated standard from the Audio
Xpress article. My friend made up the standard for 1500 umhos and 3000
umhos. He has a 539B also.

For starters, a 6V6GT will test at 3400 umhos on my tester and only 3000 on
his. When I try to calibrate the tester, the 3000 standard measures about
3350 on my tester. I can adjust the R18 resistor pot and bring the
calibration standards into line nicely. However, then when I test the
6VGGT, it tests higher, at around 3900. Other tubes test too high, also,
based on comparison to my friend¹s tester (which seems to be working
nicely).

Going through the Schoo procedure, the only voltage I found to be somewhat
off was the plate voltage. Mine read about 164 volts, rather than the
roughly 154 that it should read. All other voltages were very close in the
Schoo procedure.

Any help appreciated.

Thanks,
Steve

Hi,
I can't be of much help, as I don't work on testers on a regular
basis. Chris Haedt, who did, found countless variations in "identical"
Hickok models. He had a group of known tubes for the final sanity
check of everything that left his shop. "Calibration" will take you
only so far, with a Hickok.

73, Alan