The first thing I like to undertake when staring a restoration is to decide if I am restoring or repairing. For me a restoration is to make the unit look, and function as new again, with correct period parts and repair techniques.
A “repair” means that I am going in to do targeted repairs to make the unit work and play correctly, but not necessarily make it look like new again. This involves cleaning cosmetically of dirt, dust, debris, and whatever else as found it’s way into the set over the last 50 years. For me, this set was worthy of a restoration, at least as much possible, some components, like the old chassis mounted electrolytic capacitors are hard to come by now, and any NOS units are likely to be nonfunctional.
The next step is to document known problems with the set. Fortunately this one played, so that made things easy. Right away I noted the s meter was not operating properly, a common issue with the early National sets, noted some loud 60 cycle hum when the audio was turned down, likely a failed filter cap, and the sensitivity seems low, likely a leaking wax paper cap, and this set has a number of them. So here is where I might differ from the purist. I’ll replace the wax paper caps, and install “orange drops”, without a moments hesitation. While I admire those who will heat the old wax paper caps and hide modern caps inside, I really don’t like to take the time for this, I understand their point, but for me, I’d rather make the set look and play as well as possible.
Someone had removed, and incorrectly installed the HRO dial, a common finding, and the controls needed a general cleaning and lubrication, not unexpected after 80 years.
So my restoration plan for this set went something like this:
- Remove from cabinet, photo document any wire and components
- Check tube voltages to chart, check caps for leakage, plan on replacing all
- Thoroughly clean of the accumulated dust and grime
- Remove and test all the tubes
- Clean and lubricate the HRO dial and gearbox
- Reset the HRO dial properly
- Replace all caps needed
- Recheck voltages
- Check/adjust set alignment
- Play outside the cabinet for a few days to test, then reinstall
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