Stewart-Warner R-390A (S/N 5157)

From this...

To this...

This project started as a user-repairable from Fair Radio.  This was both a challenging and enjoyable project which was completed over several months during the winter of 2000/2001.

Restoration Details

The manufacturers, contract numbers, and serial number of the individual decks are:

The gear train was fully disassembled, cleaned, lubricated, reassembled, and mechanically aligned.  Here is how the gear train initially appeared.

Here is a picture after the gear train was rebuilt.  This gear train is very smooth.

Three reversible modifications were added.  The SSB/AGC modification was added to enable reception of SSB signals without continually adjusting the RF gain.  Two jumpers were added to the ballast tube socket to enable this receiver to use the 12BH7 tube in place of the much more expensive 3TF7 ballast tube.  An inrush current limiter was added to give the power supply a "soft" start and to reduce 120 VAC input voltage closer to the 115 VAC design value.

The PTO was disassembled, lubricated, and the internal corrector stack was adjusted to maximize accuracy across each 1000 KC band.  The maximum error at any point after calibration is 250 Hz.  The calibration oscillator was synchronized to WWV for accuracy.

The front panel was stripped to bare metal, imperfections filled, primed, painted with several coats of paint, baked, and polished.  The knobs were also stripped, primed, and repainted.  New stainless steel screws were used to remount the front panel.

All paper capacitors were replaced with new, Sprague orange drop capacitors.  The electrolytic filter capacitors were rebuilt, with new capacitors installed inside the existing aluminum cans.  All tubes were checked, and were replaced as needed.  Tube placement was then optimized based on sensitivity.  The IF and RF circuits were aligned twice, and the following sensitivity measurements were recorded.

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© 2005 by Walter Wilson, KK4DF.  All information is offered for non-commercial use without warranty, expressed or implied.