atkelar | Restoration Project #31 - Precision Instruments Model 98 VTVM (2/2) @atkelar | Uploaded January 2022 | Updated October 2024, 20 hours ago.
Part 1 is over here: youtube.com/watch?v=fOM5Zf8JaPg
Last summer, I found this old school vacuum tube voltmeter on ebay for a reasonable price. It was sold as "for parts" and the inside was shown in pictures, so I knew that it was a restoration project. Still, I had no idea just how much restoration it would be.
This video - part two of two - takes care of the meter itself, including a replacement transformer and some troubleshooting. I wonder if people like @MrCarlsonsLab or @UsagiElectric see my work and cringe or are happy about a working result... ๐ I am after all just a fan of vintage tech and want to keep it functional...
The original transformer was a bit rusty and looked quite drenched. So I didn't really trust it to begin with, and also I live in 240V land and needed a replacement anyhow. But since the voltages are quite...umm.... special, I resorted to rewinding it myself. It works surprisingly well!
The meter movement was working rather well: the current ranges worked right from the start within needle width the same value that I read on my DMM. But the other functions: not so much. The absolute values were way out and every other function wouldn't even move the needle. Since the Ohms range was working perfectly fine, I figured that it couldn't be the main tube... or at least not alone. Troubleshooting led me to a wonky trimmer that is part of the alignment circuitry.
After fixing that, I could finally get within the ballpark of the measurements; But the alingment might be off: I have to put all the trimmers to one extreme to get good readings... that doesn't seem right...
0:00 Intro - Presentation / Liberating the Chassis
1:28 Meter Movement
2:53 Selection Switches
4:44 Potentiometers / Current Sockets / Paint
6:00 Assembly: Jacks, Meter, Wire Loom
7:30 Assembly: Chassis, Battery Holder
8:58 Transformer Unwinding
10:30 Transformer Winding Adapter / Rewinding
11:60 Finishing Wires / Repacking Core / Smoke Test
12:48 Installing Transformer / Measuring / Fixing...
13:45 Mains Cable / First Tube, UB Check / Rough Check
14:50 First Test: DC Current
15:25 Second Test: Ohms
16:00 Problems in other Functions
17:25 Successful Measurements! / Packing Up / Battery Clip
18:45 Finished / Now with Sticker! / Presentation / Goodbye / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)
You can support me on Ko-Fi: ko-fi.com/atkelar
Part 1 is over here: youtube.com/watch?v=fOM5Zf8JaPg
Last summer, I found this old school vacuum tube voltmeter on ebay for a reasonable price. It was sold as "for parts" and the inside was shown in pictures, so I knew that it was a restoration project. Still, I had no idea just how much restoration it would be.
This video - part two of two - takes care of the meter itself, including a replacement transformer and some troubleshooting. I wonder if people like @MrCarlsonsLab or @UsagiElectric see my work and cringe or are happy about a working result... ๐ I am after all just a fan of vintage tech and want to keep it functional...
The original transformer was a bit rusty and looked quite drenched. So I didn't really trust it to begin with, and also I live in 240V land and needed a replacement anyhow. But since the voltages are quite...umm.... special, I resorted to rewinding it myself. It works surprisingly well!
The meter movement was working rather well: the current ranges worked right from the start within needle width the same value that I read on my DMM. But the other functions: not so much. The absolute values were way out and every other function wouldn't even move the needle. Since the Ohms range was working perfectly fine, I figured that it couldn't be the main tube... or at least not alone. Troubleshooting led me to a wonky trimmer that is part of the alignment circuitry.
After fixing that, I could finally get within the ballpark of the measurements; But the alingment might be off: I have to put all the trimmers to one extreme to get good readings... that doesn't seem right...
0:00 Intro - Presentation / Liberating the Chassis
1:28 Meter Movement
2:53 Selection Switches
4:44 Potentiometers / Current Sockets / Paint
6:00 Assembly: Jacks, Meter, Wire Loom
7:30 Assembly: Chassis, Battery Holder
8:58 Transformer Unwinding
10:30 Transformer Winding Adapter / Rewinding
11:60 Finishing Wires / Repacking Core / Smoke Test
12:48 Installing Transformer / Measuring / Fixing...
13:45 Mains Cable / First Tube, UB Check / Rough Check
14:50 First Test: DC Current
15:25 Second Test: Ohms
16:00 Problems in other Functions
17:25 Successful Measurements! / Packing Up / Battery Clip
18:45 Finished / Now with Sticker! / Presentation / Goodbye / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)
You can support me on Ko-Fi: ko-fi.com/atkelar
