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Sunday, February 16, 2014

The Restoration of Louie, the Zenith Clock Radio

Usually the old radios that find their way to my shop are just old radios; junk that no one else wants and they come in all sizes and shapes and condition. Housed in dirty, bug-infested cases with wiring that often looks like it was used by a rat lynch mob and then eaten, these pieces are usually just inanimate lumps of metal, plastic and wax.

That was my opinion until I started working with Louie, the Zenith radio.
Louie, the 1953 Zenith Clock Radio

Unlike most radios that come into my shop, Louie emanated a certain joie de vivre and looked almost new from the moment he was acquired. Made in 1953 and housed in a beautiful teal green painted bakelite cabinet, this radio was always well cared for and loved for all of its 61 years. Sadly, after the passing of its owner, it had nowhere to go and none of the family cared to keep it. Louie caught my eye immediately at an estate sale. I really liked the color and the boxy early fifties design which reminded me of the DeSotos and Plymouth automobiles of that era. Although I have previously owned and restored the lesser 515 model, this was the first higher end 622 for me.

In the shop, I did a quick evaluation and found the radio worked really well, the clock ran quietly and kept good time, and all the knobs and functions were operational. However, knowing that if no work had been done to the radio over its life, the likelihood of incipient operational issues was high. As a matter of course, I always remove and examine all radio chassis to check the condition of the wiring, the insulation and the critical components. I also test the vacuum tubes with a mutual conductance tube tester. These checks are done no matter how great the radio looks and sounds. Like most things and people at 60+ years, things are starting to wear out and joints get creaky. So even though this radio sounded great, I had concerns about long-term reliability for whomever becomes Louie's new owner.

To start, the chassis was removed from the case. With clock radios, this is a more complex operation as the clock mechanism often has to be taken out in order to remove the chassis far enough from the case to be able to work on it. This is nerve-wracking because those little plastic knobs on the clock have to be removed. Often, a previous repair has resulted in them being glued onto the stems because years of wear and tear make them loose. If that has occurred, it's literally impossible to remove the knobs without some damage. For me, it's hard to tell until I try pulling them off; and, if they're glued, it is not uncommon for the knob to break. If that happens, it's almost impossible to find an exact match replacement. So with heart in hand, I gave them a yank...and off they came, no problemo. Removing the clock assembly after the knobs are off is no more than a matter of removing the hold down screws underneath the cardboard protective backing.

The clock mechanism removed
From the start, Louie made it clear that he didn't think I needed to be messing around with his innards. Since the radio hadn't been opened in over 60 years, I didn't agree. The screws holding the back on were stubbornly stuck as were the two large chassis screws on the bottom. An impatient person would have wrenched those things off, taking bits of bakelite with them and devil take the hindmost. But the cosmetics of this radio are so fine I did not want to chance damage. So with some chiding and negotiating and little WD 40, everything came apart nicely to expose the heart of this fine radio.

Underneath circuitry as found
The first thing to do was to run tests. Almost all American radios made since the 1920's have specs that someone has published. In the early years, it was the Rider manuals, and the Beitman manuals. Later, Sam's Photofact Folders were available. Voltages and resistances within the typical AA5 circuitry are essentially the same from one radio to the next and it's not hard to guess what they should be. But different manufacturers made tweaks to their circuits for specific models and that can sometimes make a difference in how the radio performs. For that reason, I like to find the schematic for the radio I'm restoring in order to most closely approximate the range of specs called for by the original maker. Testing Louie, then, was pretty easy as I had the schematic. With the manufacturer's information, I've devised a form on which I can record the optimal factory specs from the schematic, my test results prior to messing with the chassis and the final specs after I've fixed everything. This form helps me be consistent in the steps I go through in evaluating and renewing these old radios.
My voltage and resistance test form

As it turned out, Louie was not in perfect health. A number of capacitors and resistors had dried up and were not functioning within their required ranges. As a result, a lot of electrical stress was being placed on the vacuum tubes, a good indication that the radio would fail before too long. Clearly, some renovation was in order before putting Louie up for sale.

The necessary replacements were made, all of the solder joints re-soldered and wiring with old insulation replaced.  In addition, a new polarized power cord was added to further assure safety of operation.  With this done, the radio really, really sounded nice.  The volume range was high, the tuning sensitivity excellent and the full fidelity of the radio came booming through the large speaker. It was time to perform the final tests to make sure everything was operating within specifications.

Suddenly, while checking pin voltages on one of the tubes, there was a nasty flash as the pilot light blew out and everything went dead as a door nail.  What the heck had I done?  Was there a short? Were wires touching someplace? What?

There's always a sinking feeling when something like this happens.  Old radios can be mules when it comes to behaving properly. This radio, though, had not demonstrated bad behavior.  Every new component added a layer of quality to its operation, and it seemed as happy as I with the results. So what perverse trick was it playing?
Troubleshooting sheet - Zenith radio

Troubleshooting non-working radios is a study in logic and step by step reasoning.  Since I'm not great at that, I've devised a method and format for uncovering circuit faults. Luckily, in this instance, it turned out that one of the tubes had failed. This was fine since I was replacing all of them anyway.

As soon as the new tube was plugged in, everything returned to normal and the radio sang like a bird (but without the chirps and squeaks that can be annoying in anything but birds)

Now it was time to turn attention to the case.  The paint job after 61 years was in remarkable shape.  No renovation was needed; just cleaning.  The case was cleaned thoroughly inside and out and some of the inner insulating paper glued.  The gold colored grill was cleaned bar by bar and all the knobs done over with a toothbrush.  After it all dried, a coat of protective carnuba wax was applied to everything. The loudspeaker was treated with a special coating I've formulated to restore flexibility and add strength to the speaker paper.

All the components were re-set back in the case, the pointer knob aligned and the clock movement lubricated.
Case parts after cleaning and wax
Although Louie can't talk, he can certainly sing and there's no doubt that whenever you turn on his switch, he couldn't be happier. The warm tube driven AM sound is full and sharp and his little pilot light shines strong and steady for hours and hours.  His clock with the copper motor runs silently and keeps excellent time and all his alarm and radio on-off functions work as they did when he was new.

Through the mid-1950's, Zenith, one of the biggest name in electronics,  made some of the finest consumer radios available. They were colorful, innovative, great sounding and solidly designed pieces that could work anywhere with any decor. Zenith radios were the choice of many radio repairmen.  Louie, the Zenith radio is a great representative of those times.

© David Simons, Feb. 2014