atkelar | Restoration Project #33 - Precision Model 612 Tube Tester - Part 2/2 @atkelar | Uploaded April 2022 | Updated October 2024, 16 hours ago.
I got some vacuum tube based projects in my pipeline and might get more of those over time... so I decided to go for a "tube tester", which were quite common in the days of tubes. There are different categories of those: simple short and heater testers that might include a "yes/no" light indicator to show that they are doing something; on the other end of the spectrum are complete classification devices that can accurately measure tubes. Neither of which makes sense for my intended purpose. I want a bit more than a pure yes/no result but I don't need a full lab setup either. So the third category in the middle was my choice: an emission tester. These heat up the tube and put a current through it, connected to an analog readout to show how good or bad the tube is, compared to its "should" current.
As a complete random coincidence, I found a Prcision Instruments - or Precision Apparatus? I've seen both names on plates and documents - model 612; It is a rather versatile device in this category and it fits the Precision VTVM that I restored last year perfectly! Exact same case! Down to the two random holes in mine, which are used in this one, so now things make sense!
This is part two (of two) and in this one I'm finishing the assembly of the tester and show how the buttons are used to measure things; except the capacitor test, since I'm not sure it is all that helpful, and I don't have any test subjects around right now;
A note about the "permanent" magnet issue: I am aware that hard knocks and heat might "weaken" them, so I took care that the dremel cleaning wouldn't get them hot to the touch... I am at a loss why they lost so much strength. But the added rare earth magnets do the job nicely. It is back to linear 0-2-4mA display characteristics.
Also, some of the contacts where so much oxydized that even a Dremel and wire brush wouldn't help: I had to use a file and sandpaper for some...
I saw @MrCarlsonsLab use one of these recently (an older video, I just saw it after I got my version here) - would love to hear what he thinks of my work; even if it doesn't quite measure up to his standard...
0:00 Intro / Meter Assembly
2:33 Meter Test / Calibration
4:09 Potentiometer Cleaning
5:48 Push Buttons
7:17 Toggle Switch
8:27 Capacitor Replacement / Painting Base Plate
9:15 Tube Cap Contacts
10:12 Solder Resistant Resistor
10:45 Switchboard / Voltage Selection Switch
12:15 Assembly Time! / Banana Jacks
13:00 Tube Sockets: Mounting / Wire Loom
13:59 Transformer
14:45 Switch Bank Mounting / Knobs
15:39 Battery Tester Test! / Tube Database Cleanup and Cover Sheet
17:18 Tube Sockets: Soldering / Finalizing Packaging
18:15 Calibration Procedure
19:27 Battery Test Example
19:50 Tube Test Example
21:00 Finished Overview / Summary / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)
You can support me on Ko-Fi: ko-fi.com/atkelar
Calibration Guide found here: oldradios.50webs.com/precision/600/612cal.html
Compiled test data list: oldradios.50webs.com/precision/600/600_series.pdf
I got some vacuum tube based projects in my pipeline and might get more of those over time... so I decided to go for a "tube tester", which were quite common in the days of tubes. There are different categories of those: simple short and heater testers that might include a "yes/no" light indicator to show that they are doing something; on the other end of the spectrum are complete classification devices that can accurately measure tubes. Neither of which makes sense for my intended purpose. I want a bit more than a pure yes/no result but I don't need a full lab setup either. So the third category in the middle was my choice: an emission tester. These heat up the tube and put a current through it, connected to an analog readout to show how good or bad the tube is, compared to its "should" current.
As a complete random coincidence, I found a Prcision Instruments - or Precision Apparatus? I've seen both names on plates and documents - model 612; It is a rather versatile device in this category and it fits the Precision VTVM that I restored last year perfectly! Exact same case! Down to the two random holes in mine, which are used in this one, so now things make sense!
This is part two (of two) and in this one I'm finishing the assembly of the tester and show how the buttons are used to measure things; except the capacitor test, since I'm not sure it is all that helpful, and I don't have any test subjects around right now;
A note about the "permanent" magnet issue: I am aware that hard knocks and heat might "weaken" them, so I took care that the dremel cleaning wouldn't get them hot to the touch... I am at a loss why they lost so much strength. But the added rare earth magnets do the job nicely. It is back to linear 0-2-4mA display characteristics.
Also, some of the contacts where so much oxydized that even a Dremel and wire brush wouldn't help: I had to use a file and sandpaper for some...
I saw @MrCarlsonsLab use one of these recently (an older video, I just saw it after I got my version here) - would love to hear what he thinks of my work; even if it doesn't quite measure up to his standard...
0:00 Intro / Meter Assembly
2:33 Meter Test / Calibration
4:09 Potentiometer Cleaning
5:48 Push Buttons
7:17 Toggle Switch
8:27 Capacitor Replacement / Painting Base Plate
9:15 Tube Cap Contacts
10:12 Solder Resistant Resistor
10:45 Switchboard / Voltage Selection Switch
12:15 Assembly Time! / Banana Jacks
13:00 Tube Sockets: Mounting / Wire Loom
13:59 Transformer
14:45 Switch Bank Mounting / Knobs
15:39 Battery Tester Test! / Tube Database Cleanup and Cover Sheet
17:18 Tube Sockets: Soldering / Finalizing Packaging
18:15 Calibration Procedure
19:27 Battery Test Example
19:50 Tube Test Example
21:00 Finished Overview / Summary / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)
You can support me on Ko-Fi: ko-fi.com/atkelar
Calibration Guide found here: oldradios.50webs.com/precision/600/612cal.html
Compiled test data list: oldradios.50webs.com/precision/600/600_series.pdf
