Originally posted in December, 2018
This post documents my restoration of the Hickok 209A VTVM, SN 1333254.
Outside visual inspection results:
- Overall good visual condition outside
- Meter appears to move freely and does not stick
- Meter face is excellent and there are no scratches on the glass
- Meter bezel is dirty, but does not appear to be corroded
- Area of corrosion noted at bottom of case
- The case has some minor paint scuffs and nicks accumulated over the past 60 years
- Line cord appears to be original and looks to be in good condition
- Has an original rubber grommet where the line cord enters the case
- No obviously broken parts: lamp, pin sockets, dials are in good condition
- Has DC Probe (reads 3.36 M ohms)
- No AC probe but does have the 4 wire AC probe connector
- No pin tip test leads
- Controls and switches all operate smoothly
Inside visual inspection results:
- Overall inside condition looks good
- No evidence of prior repairs or modifications
- Appears to be all original components including carbon composition resistors and paper, mica and electrolytic capacitors
- Glyptal paint on each solder joint was intact
- Uniform coating of dust on all interior surfaces
- Serious corrosion issue with the battery holder (no batteries installed)
- Chassis corrosion damage restricted to battery holder itself
- Some corrosion damage to the inside and outside of the case, but it appears to be surface corrosion and minor pitting only
- Unit has no line fuse, nor any provision for one
- Unit has a 500v mica line filter capacitor
- Unit has a non-polarized plug
From the above images, it is clear that the battery holder will require some corrosion mitigation and restoration. Fortunately, it is restorable as the parts are of heavy gauge (including the spring contacts) so that material lost to corrosion will not comprise the overall mechanical integrity.
The plan for this restoration is:
- Closer visual inspection of the chassis for any subtle problems I missed on the first pass
- Repair/restore the battery holder
- Check the meter movement with a power supply, limiting resistor and good ammeter
- Check the carbon composition resistors to determine if they need to be replaced. If they do, use 1% metal oxide resistors of equal or higher wattage
- Replace all the electrolytic/wax/paper/foil capacitors and possibly the mica capacitors
- I don’t intend to replace any divider resistors unless I have some linearity or range issues
- Put in a line fuse inside the cabinet
- Replace the mica filter capacitor with a modern Y rated capacitor
- Fit a polarized two prong plug
- Run the curves of the bridge tube and check the balance
- Check the other tubes and replace as needed
- Clean up the chassis
- Clean up the front panel and meter bezel
- Clean up the cabinet (restoring and/or repainting will have to wait until spring)
- Clean the switch contacts, pin jack contacts
- Fabricate an AC probe (I have the parts for this)
- Fabricate Ohms+Milliamp probes
- Check the meter mechanical balance
- Calibrate the unit
To be continued in Part 2……