Hickok 209A VTVM Restoration Part 3
This the third part of an “N” part series documenting my restoration of the Hickok 209A VTVM, SN 1333254. Hickok 209A VTVM Restoration Part 3, corrosion issues and restoration plan.
As mentioned in Part 2 of this series, a visual inspection of the chassis of the 209A revealed a serious corrosion problem with the battery holder. The corrosion had migrated to the bottom of the case but not to the remaineder of the chassis. There were no batteries in the unit when I received it.
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 4, thanks for reading.