Greetings friends,
Recently, I lucked out and received a very cool vintage metronome from someone in my local "Buy-Nothing" group. As some of you know, music is a big part of my life and I was very excited about this find and at the prospect of restoring it to fully-functioning condition.
Let's start with a little bit of history on this device, since it has some cool design features and is one of the first electronic metronomes to hit the market. The Franz electromechanic metronome was invented in 1938, and saw production through 1994. The mechanism by which the metronome operates is very interesting in that it uses a synchronous motor to spin a wheel which drives a shaft containing a ledged cam lobe (not sure what else to call it?), which on each rotation strikes a spring-loaded hammer onto the interior wall of the metronome box. Changing the angle of the wheel with respect to the motor spindle by way of the external dial ("selecting the tempo") changes the frequency of the hammer strikes.
The metronome I received was in fairly good condition, but with a fair amount of dirt on the exterior. The mechanism worked well at higher tempi (80+ bpm) but was very irregular at slower tempi. The bottom plate, seen above, is in good enough condition that I won't be altering anything about it during this restoration. I'm happy that the label is legible, so I won't try risking any damage to it by trying to clean it. I'll just have to live with the small amount of rust.
To start the restoration, I disassembled the entire mechanism and right away cut the old power cord which was very brittle and starting to crack in some places. I bought a cheap 8-foot extension cord to re-purpose as the power cord for the metronome. The socket is interestingly designed, and it's plenty obvious how the cord connects. The other end gets soldered to the switch and motor, which we'll see later.
To clean the exterior, I started off with simple dishsoap and warm water, and used an old toothbrush to get into the dirty crevices. Since the white lettering was oxidized and already chipping out a bit, I decided to just scrub until all the letters were cleaned out. With all the dirt removed the appearance of the case was already hugely improved, but I decided to polish a little bit using rubbing compound just to give it a little bit of shine.
The mechanism itself was quite clean and didn't require a whole lot of manipulation, though I did need to make some adjustments to make the slow tempi more consistent. I noticed that at the lower settings the wheel that operates the hammer was not making full contact with the motor spindle. To fix this I simply cut some pieces of thin leather to act as shims, which lowered the height of the motor and allowed the hammer wheel to make full contact across the full tempo range.
I used a lacquer-stik to fill in the numbers on the face on the metronome as well as the "ELECTRONOME" lettering underneath the dial (although these didn't seem to be filled when I received it). The metal indicator on the dial was polished using Brasso, and the reassembly went without a hitch.
Fully functional again, the metronome has a permanent place on my piano. I use it occasionally, especially when showing off to guests. After 80 years of use, it's great to see some new life in this metronome!
Thanks for reading,
Juju
References:
1. http://www.franzmfg.com/history.htm