National HRO 5TA1 - Spring 2004
Click on photos to enlarge.
Lately my radio interest has harkened back to the older and older gear. Past the 1950s vintage, back to the black crackle paint of the 1930s.
The latest project to grace the workbench of W1UJR is a classic 1930 receiver from National, a HRO 5TA1. HRO’s are distinguished by their large trademark micrometer tuning knob and plug in coil sets. As found, this was a nice receiver, complete with speaker, doghouse power supply and four coil sets.
The unit was nice in the sense that it was mostly original, but in dire need of a good cleaning and replacement of the old paper capacitors. Unfortunately at some point in its life, a previous owner had drilled the cabinet and installed an auxiliary S-meter adjustment potentiometer. An xtal calibrator was also added; fortunately this was both simple and straightforward to remove. My goal was to return the HRO to its original state and use in my 1930 station. Although I understood the logic and perhaps need for these modifications, they did not fit in keeping with that restoration plan.
I carefully removed the cabinet sheet metal and front panel, perhaps for the first time since the receiver was assembled nearly 60 years ago, noting the various fastener locations for reassembly. Once free of its dusty cabinet, it was a simple matter to clean the chassis of the unit with my standard mix of citrus based cleaner and Windex. The hardware retaining the IF cans was then removed so I could clean up to and under the cans. The key to a good restoration is a clean chassis. I covered the various marking and labels on the chassis with masking tape to prevent their removal by the cleaning agents.
Once I had the chassis
cleaned, it was time
to tackle the grimy and binding air variable tuning capacitor. To
facilitate cleaning and lubrication during the restoration process the
large air variable tuning capacitor was removed from the chassis. This
is not so much a project as it sounds as there are only four wires
soldered to the unit, and four screws to remove. Once free of the
chassis, the unit was then given a run through the dishwasher. As
interesting as Millen's dial is, the gearbox design is really what makes
this radio so unique. The ball bearing worm drive and split spring
loaded gears serve to minimize backlash while the famous National PW
dial provides excellent frequency discrimination and silkily smooth
There are two caps under the small air variable used for the BFO. I left these for last, thinking that they would be a real challenge to access. From the bottom of the chassis one could barely see the two caps, hidden as they were under the air variable. Surprisingly these proved very simple to replace. I was able to unbolt the BFO capacitor from the front panel, and without unsoldering any wires, lay it back on the chassis, allowing excellent access to two formally hidden caps.
With the caps replaced and the tuning capacitor reinstalled on the chassis, it was time to tackle the installation of the unique HRO tuning dial.
A few words about James Millen's wonderful tuning dial. Obviously National went to great lengths to design and build such a wonderful tuning system, but simple as it is it still remains a mystery to many hams. This receiver and several other HROs which I later acquired have had these dials incorrectly installed. The classic giveaway to this fault is dial numbers that do not line up in the window. Once you understand the gear alignment, this is simple to correct, and most of the dials can really benefit from a removal, cleaning and lubrication. W0VLZ's site offers excellent instruction on the reinstallation of the HRO dial.
With the electronic work now done (be sure not to miss the bypass cap on top of the chassis, under the left side of the air variable), it was time to turn my attention to the cabinet. I cleaned the surface with my citrus cleaner, lightly scrubbing where needed. Black crackle has an amazing ability to hold in the dirt, and sometimes careful but firm scrubbing is the only way to properly clean it. After cleaning both the inside and outside of the sheet metal cabinet, I then applied "Cockpit Cleaner", a product manufactured by Wurth USA. I have used this product with great success, although designed for automotive use, it really makes the black crackle look like new, and it repels dirt and dust at the same time. I have not corrected the hole that the previous owner has drilled for the potentiometer modification, but as it is on the side of the cabinet it is not a concern.
The restored HRO both looks and plays great on the bench next to the Johnson Valiant. I have a Harvey Wells TBS-50 transmitter awaiting restoration. My plan is to pair the HRO up with the TBS-50, two great black crackle radios from a bygone era.
Remember, real radios glow in the dark!