- 2024
- Oct
- 30
A Waterman OCA-11A “industrial / pocket” oscilloscope.
This little scope came from the recent MARC hamfest, and was sold as not working - the previous owner stated that someone had removed tubes, and all he did was verify the heater in the CRT was lighting up. He was right, someone removed all of the 12AX7 tubes as well as a 6U10 compactron, leaving only a 6AG11 compactron in place. All of these devices are triode amplifiers, with the 6AG11 having two diodes in addition to the triodes.
The device appears to have a solid-state power supply with solitary diode. There’s some small evidence of repairs being made over the years, but for the most part it seems to be fairly original.
Tube compliment for this device is:
4x 12AX7 dual triode
1X 6U10 triple triode
1X 6AG11 dual diode/dual triode
The device is capable of operating on 50-400Hz @ 115VAC
The front offers all the controls, and uses pin jacks for input on a strip at the bottom. That’s kind of unusual. The metal under the paint appears to be oxidized, and the enamel with the lettering is flaking off. The potentiometers are brought out to the front by long internal shafts, some of which are bent. This could be an easy fix, as they’re just connected internally with nylon unions.
The back offers a cord wrap and some screw terminals, presumably for grounds. It also offers a badly exiting cord from the previous owner.
The device is relatively clean inside with the transformer, power supply, and high voltage all riding in the back.
The bottom is well packed, but there’s no wax paper stuff as far as I can see. Looks like films and other decent capacitors, but I bet some of those carbon comp resistors are drifting. There’s an electrolytic that’s probably baked out, and some neon bulbs of unknown type probably being used as regulators that would need to be replaced, but that’s about it.
You can see where the previous owner removed all of the “good” tubes. The 6AG11 is also a triode pair, so I’m not sure why they didn’t remove it as well. Fortunately, if you’re not concerned about the make of the tubes, all of them can be relatively cheap - there’s about $25 worth needed for this device.
It’s an interesting little scope, and would be perfect for a benchtop radio repair station - tube scope with tube inputs doesn’t care if you hit B+ for a second.
I think I may give it a shot and see if it will live again. If someone out there has a schematic for this unit, I’d appreciate a copy.
Next part of this series: https://wereboar.com … oscope-part-2-tubes/