Once again we have here in the RA66A, a very desirable piece of kit.
The RA66 is used to visually display signals in any 1mhz wide band from 1-30mhz using an RA17 receiver. The Cathode Ray Tube fitted to the RA66 can be adjusted to display between 1mhz to 100khz of spectrum and controls can be adjusted to centre the display on any part of this spectrum. Sweep time can be adjusted to 2,1,0.5,and 0.2 seconds (RA66B only). Signals can be displayed with bandwidths of 1.2 , 3 and 8 khz. Sensitivity will give 1" deflection on the CRT for 4uv input to the RA17. To aid tuning a marker can be set which will track the vfo on the CRT as the RA17 is tuned, and fixed markers can be switched in covering intervals of 100khz.
Unfortunately this is one adaptor which cannot just be connected to the RA17.A buffer amplifier is needed to connect between the RA17 and the RA66.This is called the MA251 and it is fitted on to the main chassis of the RA17 and connects electrically between the second and third mixers.Alterations have to be made to the I.F strip and also to the A.G.C. Once made these alterations affect the signal handling characteristics of the receiver. Something a UK reviewer should have known about before criticizing Racal's AGC system.
.These modifications are well worth the effort,watching the CRT and seeing signals appear and disappear is quite interesting,as is watching a signal suddenly appearing and then immediately tuning to it.
Here is a picture of an RA17 fitted with the MA251
The MA251 is the assembly screwed onto the main chassis and is fitted with a single valve. It is in the center of the picture.
Here we have 100kcs sweep centered on
1.250 mhz . 
This image shows the full 1mhz sweep from
1-2mhz.
There are three variants listed by Racal. RA66A for the RA17, RA66B for the RA17 and Mufax Recorder and RA66B-1 which was modified with all American valves , plugs and sockets.
Last updated 05/03/2002