Restoring an RA-117 is a long and involved project compared to more-typical shortwave receivers. Following are some general notes, and some examination of the various sections of the receiver. Alignment is discussed on a separate page.

Capacitors

Resistors

In the tradeoff between making an assessment of the resistors and deciding which ones to replace versus simply replacing them all, the latter approach may well be preferable.

Chassis Compartments and Modules

Main Chassis 1st VFO Subchassis Harmonics Generation Compartments

2nd Mixer Compartment 2nd VFO Subchassis 3rd & 4th Mixer Subchassis

100 KHz IF & Detector/AVC Crystal Calibrator Module Power Supply & Audio Compartment

Main Chassis

Bottom of bare chassis.

Bare chassis with components.

Main chassis completely stripped and ready for reassembly.

The receivers are based on a large cast-aluminum chassis, with several cast-aluminum sub-chassis mounted onto the main chassis.

As can be seen, the 100KHz IF strip is also removable.

Ready for final assembly.

Modules and other bits.

Rebuilt main chassis and major modules prior to final reassembly.

During any significant rebuild of the main chassis, removing or leaving off the power transformer and choke as well as other modules makes the chassis much easier to maneuver and handle.

Not shown are the side, top and bottom panels.

FRONT

REAR

Views of reassembled chassis.

LEFT

RIGHT

BEFORE

REBUILT

Bottom views of chassis. In the photo of the original, the power supply compartment has already been cleaned out.

System switch: The system switch may look like a typical rotary switch, however it actually has special make-before-break contacts. The system switch controls the main B+ line in the S5.1L section. If this line goes open arcing can result as current is interrupted through the filter choke. The make-before-break contacts are intended to keep a load on the supply as the switch is rotated between positions, in contrast to normal break-before-make contacts which would open the line briefly.

Arc-damaged contacts have nonetheless been observed on one original switch, leading to greater arcing and deterioration as the contact is eaten away and the make-before-break facility is lost.

In one unit the original system switch was missing. Replacing it with a normal break-before-make type (the white-wafer unit seen in the first rebuild here) resulted in significant arcing. It was subsequently replaced again with a proper type.

It is possible to remove the switch and rotate the wafers to provide a 'good' set of contacts on the B+ line and move the bad set to another position where the make-before-break facility is not of consequence, although removing and working around this switch is not easy.

REBUILT

Switch compartment.

The completed, fully rebuilt chassis, including new wiring harness.

In this instance the circuitry was modified to eliminate two poles on the system switch, so only two wafers (4 poles) are needed, rather than 3 wafers.

One of the toggle switches dismantled for cleaning and lubrication, showing all the tiny parts involved.

1st VFO Subchassis

1st VFO Module

REBUILT

The 1st VFO sub-chassis or module actually contains the megacycle-range Variable Frequency Oscillator, the RF front end (tuning and amplifier), and the 1st Mixer.

RF compartment, PARTIALLY REBUILT

RF Compartment, REBUILT

Closer views of the RF compartment of the 1st VFO.

Oscillator compartment, PARTIALLY REBUILT

Oscillator Compartment, REBUILT

Closer view of the oscillator compartments of the 1st VFO. The 1st mixer is also located in the oscillator compartment.

Apparently Meccano wasn't just a child's toy. The gearing on the 1st VFO actually uses bits of Meccano. (The Meccano label is readable in the larger version of the photo).

Harmonics Generation Compartments

BEFORE

REBUILT

Harmonics generation compartment.

Change: the 4.7K resistor originally mounted between two tabs on the coil is moved below and connected directly to the component board. The 47K resistor stretching way over to V1 is now mounted in this place and a wire connects over to V1.

BEFORE

REBUILT

Harmonics mixer compartment.

The small aluminum separator panel is best removed for access during the rebuild.

2nd Mixer Compartment

BEFORE

REBUILT

2nd Mixer compartment.

BEFORE

REBUILT

Component board and the little compartment for the plate circuit components of V9 (2nd Mixer).

Note two 0.001 caps stacked for compactness.

2nd VFO Subchassis

2nd VFO Module	Tuning Compartment
BEFORE	REBUILT

The KILOCYCLE tuning mechanism involves 13 ball-bearing races. Various portions of the mechanism may require dismantling to clean off old grease and run the bearings to work new lubrication in. The shafts and gears are assembled with small drift pins, and in a particular sequence; the mechanism does not come apart easily.

In working on one unit, three issues needed to be addressed to get it running freely and smoothly:

The grease in the bearing races may be dried up, causing a 'chunky' feeling as they rotate. A small drop of light oil in each one may free them up. A sticky grease was found around the shafts of the film-scale reels. The reels are tensioned by springs connecting the reels to the tension-balancing gears above them. The sticky grease affected both the rotation of the reels and dampened the spring tensioning. Alcohol was used to clean these bearing surfaces. There is a thrust bearing at the top of the vertical shaft holding the film-scale drive sprocket which may need greasing and adjustment.

Electronically, refurbishing the 2nd VFO is quite straightforward.

3rd & 4th Mixer Subchassis

Ready for assembly.

Under assembly.

While not too critical in that the RF frequencies involved are relatively low, this is a very awkward module to work on due to the cramped interior.

BEFORE

REBUILT

Views of 3rd and 4th Mixer subchassis. The internal separator panel has been removed to improve access.

BEFORE

REBUILT

Several paper capacitors are buried underneath other components. Some reorganising of the layout has been done here to improve access slightly (observe new ground lug at base of terminal post in center of side seen to the rear).

BEFORE

REBUILT

Shown at the far end below the black connector block is a slightly altered wiring layout connecting the two 1.6MHz IF filters. A 0.005 disc capacitor replaces the original paper type.

100 KHz IF & Detector/AVC

BEFORE

REBUILT

100 KHz IF strip components left.

Note all the missing paper caps in the 'original' photo, these had already been stripped when the receiver was received.

BEFORE

REBUILT

100 KHz IF strip components right.

Stripped.

Components ready for re-assembly.

In this instance the 100KHz IF strip was completely stripped and rebuilt.

Top/component side.

Bottom/wiring side.

New component boards for the IF and Power Supply/Audio sections.

The original IF boards had been broken during the 'de-milling' process. Some reorganisation of the components has been performed so the component ordering does not match the original exactly.

The Power Supply/Audio board is a new design to replace the original point-to-point wiring in that section.

Amp load, BEFORE.

Amp load, REBUILT.

Output coil for secondary IF amp.

BFO, BEFORE.

BFO, REBUILT.

Gaining access to the BFO for component replacement requires unsoldering and removing the unit. Alternatively, access may be adequate if the entire IF strip is removed from the main chassis.

Forward half, REBUILT.

Rear half, REBUILT.

The fully rebuilt and installed 100 KHz IF strip.

Crystal Calibrator Module

BEFORE

REBUILT

Redoing the little crystal calibrator module is straightforward. Some minor modifications to the wiring were performed: the post in the upper-right of the component board was used for the B+ bypass capacitor rather than as a tiepoint for the output signal, and a duplicate ground lead was not replaced.

The unit shown was actually from an RA-17, note the funny coax connector in the picture of the original. For use in an RA-117 it was rebuilt with a BNC connector. The little mounting bracket on the end opposite the octal plug also had to be remade as the thumb-screw mounting hole on the 2nd VFO was moved about a quarter of an inch from the RA-17 to RA-117.

BEFORE

REBUILT

Power Supply & Audio Compartment

BEFORE	REBUILT
BEFORE	REBUILT

The power supply/audio compartment of the 5 units we worked on suffered from corrosion of wires and component leads, along with brittle and cracked insulation on wires. Heat would appear to be the primary culprit, exacerbated by a salt-air (naval/coastal) environment. There is over 8W of heat being generated in the enclosed compartment from resistors in the power supply.

In the instances shown, the compartment was completely stripped and all RC components replaced. The layout was redesigned to clean up some of the wiring. Two redesigns are shown.

The first uses common terminal strips to hold the new axial-lead filter caps and other parts of the power supply, along with a new component board (seen on the left in the photo) to hold the audio cathode-circuit and feedback components. This space was originally occupied by the power supply filter electrolytic capacitors. This arrangement has the benefit of better separating the audio and power supply circuits: the wires to the power supply filter caps do not have to traverse through the audio area.

The second redesign incorporates a new component board holding almost all the smaller RC components of the power supply and audio sections.

Power resistors.

Power resistors, and modern IEC connector.

In both redesigns of the power supply / audio compartment, to solve the heat problem, the power resistors were moved out of the compartment to the top of the chassis, occupying the space where the rectifier tube was located in the RA-17, an area left empty in the RA-117. Shown are two methods of installing the three power resistors.

Note also the IEC power connector in the one photo. There is just enough room on the back panel of the chassis between and below the two fuses to install a standard IEC power connector if one is so inclined, to replace the original fixed line cord. Some may not like such a 'modern' alteration, but I can't stand equipment with dangling power cords.