Racal RA-117

The RA-17 was introduced in the mid-1950's, the RA-117 followed a few years later. Some revisions and modifications were made to each model during it's production lifetime. Some of the differences are minor - slight circuit improvements - others are more significant. There is not always much in the way of labelling to distinguish the revision level of a particular unit, a detailed examination may be necessary. Even examination of the front panel may not be enough to ascertain whether a unit is an RA-17 or RA-117.

From the five RA-117 units we saw, there seem to be two versions. The units are not labeled as being different - they are identified only as model "RA-117". The most easily discernible change is the removal of the pre-selector "0.5-1" range, to be replaced with a "WIDEBAND 75Ω" range. This seems unfortunate in that being able to tune the preselector for a given frequency significantly reduces the noise level. Without the "0.5-1" range even strong AM broadcast stations are noisier than they would otherwise be.

Below is a list of the known and observed differences.

Section or Issue RA-17 Earlier RA-17 Later RA-117 Earlier RA-117 Later
Sample serial numbers     N8, N16 N0115, N0144, N0714
1.6MHz IF Not present. The 2-3 MHz IF is mixed with the 2nd VFO to produce the final 100 KHz IF. The 2-3 MHz IF is a tuned filter involving multiple sections on the KC (2nd VFO) tuning cap. A fourth conversion stage with an IF frequency of 1.6 MHz is inserted between the 2-3 MHz IF stage and 100 KHz IF stage. This involves the addition of 3 tubes and another small sub-chassis. The 2-3 MHz IF filter is a fixed bandpass filter. The 2nd VFO is altered considerably: the frequency span changed, and the variable cap reduced to a single section, for the oscillator.
Power supply rectifier Tube. 4 solid-state diodes in a bridge configuration. A power resistor is also placed in the secondary/rectifier circuit with the unfortunate consequence that it adds significantly to the heat generation in the enclosed power supply compartment.
Front panel meter switch Two-position toggle switch selects RF and Audio Levels. Three-position rotary switch adds S Level.
Preselector RF RANGE switch Ranges include a "0.5-1" MC/S position. Position is replaced with a "WIDEBAND 75Ω" setting. An according coil and trimmer cap are removed from the 1st VFO sub-chassis.
1 MHz oscillator / V1 Cathode feedback.
No external 1MHz input.
Oscillator configuration changed to screen-grid feedback.
External 1MHz input added.
Minor changes to RC values.
Harmonics Generator / V2 V2 is 6AU6. V2 changed to 6AK5.
Minor changes to R values, V2 cathode RC & screen C added.
Harmonics Generator / V2 C7 is a gimmick cap in parallel with the plate coil of V2. C7 changed to a 10pF trimmer.
1st VFO / V5 V5 is 6AU6. V5 changed to 6AK5
Minor changes to RC values.
V5 changed to 6BA6.
Minor changes to RC values.
37.5 MHz Amp / V6,V8 V6 & V8 are 6AU6. V6 & V8 changed to 6AK5.
Some changes to RC values, cathode & screen caps removed from V6.
V6 & V8 changed to 6BA6.
Some changes to RC values, cathode & screen caps added back to V6.
2nd Mixer / V10 V10 is 6AU6. V10 changed to 6AK5.
Cathode R value changed.
V10 changed to 6BA6.
Minor changes to RC values.
2nd Mixer / V9 - Single BNC socket at the output of V9, which is then split via a BNC T connector to feed the backpanel RF socket and the 2-3 MC/S Bandpass Filter. Two BNC sockets and some additional componentry in the plate circuit to feed them.
2nd VFO (?) Not examined. One of the screws holding the 2nd VFO to the main chassis is screwed in from above, inside the cover on the 2nd VFO. The screw goes in from under the main chassis, making it easier to remove.
3rd Mixer / V25 - V25 suppressor grid is connected to cathode. V25 suppressor grid is connected to ground.
4th Mixer, 1.6MHz IF / V26 - Secondary of 2nd transformer in 1.6MHz IF filter feeds V26 via a capacitive divider, with a 270K resistor from pin 7 of V26 to ground providing bias. V26 is fed from a tap on the secondary, no bias resistor necessary.

  Technical | Versions | Rebuild | Alignment
Racal RA-17 & RA-117
2008 Jun