[Premium-Rx] Racal 1778

[Dan Rae]

ik3glf at virgilio.it wrote:
> Hallo all,I've the chance to purchase a RACAL 1778 that I was searching since long time. I can choose from two of them, one has the AFC "disconnected" (the owner says it was done to improve the functionality of the receiver) but have a better "AM FILTER", the other does not have the "BETTER AM FILTER" but it is unmodified with the working AFC.
> Does somebody out there know a reason for this modification?
>   
Time was I would have had my wrist slapped for mentioning such an old 
receiver on this list :^)

The AFC in these and the parent 1772 is essentially useless in these 
modern times with stable frequency standards available to all.  In the 
days when for example the BBC world service distributed it's programme 
material using SSB with 6 kHz wide filters and a pilot carrier and for 
some RTTY systems, then yes, it had a use. 

The AFC uses one of the positions on the filter board for a 100 Hz wide 
carrier filter.  Links are available for using this filter or another in 
the same position on the board in the main signal channel.  This can 
give you an additional AM / CW width by adding another position to the 
filter switch.  This is relatively easy to do by moving the switch end 
stop; the contacts are on the wafer and I'm pretty sure the wiring to 
the filter board is also there, if not it is easy to add.

I've no idea what the "improved" AM filter is.  A while ago I found a 
bunch of really good 8 pole nominal 6.8 kHz wide filters for these, some 
of which I sold to cover my costs, including even one to Italy, and the 
rest I shared out to friends.  If it is one of these you are lucky.  
Also some of the ex RAF receivers had only a 3 kHz width available, not 
a lot of use for AM, this may be what you are referring to.

In any case the filters are easy to change, the hardest part will be 
changing the legend on the transparent skirt of the switch to match what 
you have.

So, in summary, disabling the AFC is basically just a link on the Filter 
board, and easy to reverse if you keep the filter in place.  Filters can 
be inspected simply by raising the board which hinges up and looking.  I 
would think that the first of your two choices of radio was the best.

Factors of more importance in your choice should be the condition of the 
PVC wiring round the power supply area; has the insulation hardened and 
gone brittle?  Most of these will need some replacement of the wiring, 
if not now, then soon. Also beware of the NiCad memory battery, although 
it is on a separate little board it can still leak and do damage.  Non 
leaking NiMH replacements are available from Varta.

The manuals are hard to find, if you can get a paper one with the radio 
then do so.  I know of no electronic versions.

Dan

ac6ao / g3ncr and owner of too many Racals...