The Precision ST-22 Signal Tracer Part 1: Observations.
Monday, April 6, 2026 at 08:39:44
This is a device I picked up at Dayton 2025, mostly because it was cheap, and was being ignored because it was very dirty and wasn’t a desirable EICO unit.
This is how I found it:
And how it cleaned up. It was missing a knob so I pulled a gray PACO knob from my stock. Same knob, different color. Yeah…the selector control should have had a different color on it, that’s the way it is…
This one might have been a factory build. There are names on everything as if multiple people had their hands in this.
The tube compliment, save the eye, is all Precision or PACO branded. Either this has it’s OEM tubes from the original sale, or the owner replaced like-for-like.
The bottom of the unit is quite lovely. All those old Dumont capacitors, tho…
Notice all of the holes are grommeted for wires. Quite a different level than other manufacturers.
Even the eye tube is held in with a band made of wire.
But…
Fortunately, the chassis is return, but that still probably caused some noise.
Some basic checks on the unit before applying power…
That one is no good.
That one is ok. Kind of.
I’ll have to do some other checks with voltage later. I’m curious as to how well the Dumont capacitors held up.
There is one part, however, that needs to go, and that’s this across the line capacitor:
A new safety rated part was installed.
So…does it work? Sure does:
The eye tube is just about as dead as can be without being unusable, so this thing has a lot of hours on it. The gain control has a thunderstorm in it after multiple cleanings, so that will need to be replaced. Other than that, if may be a use as-is assuming the electrolytics don’t go popboom. I’ll still do some diagnosis on it to see if any resistors are way out of tolerance, or any of the other capacitors leak. Some will need to go, but the rest? Who knows.
This model seems to be somewhat unusual. The PACO Z-80, which looks like this one save it doesn’t have the chart diagram on the left side, appears to be identical. I can’t find a manual listed as the ST-22, so I’ll compare to the Z-80’s schematic and see if they are the same.
Stay tuned, this one will be on the bench maybe later this year if I have the time.
Next part of this series: Coming soon.