[Premium-Rx] Racal 177x PSU

[GandalfG8 at aol.com]

In a message dated 08/08/2010 17:52:25 GMT Daylight Time,  
john at crew-green.com writes:

Replacing D2 may be worth doing, especially if one can find a  Schottky
bridge, but there is another PSU modification that's even more  important.
All the RA177x family are excellent from an RF point of view but  the
youngest is now around thirty years old and many have led hard lives  in
professional service. Unfortunately some aspects of their mechanical  and
electrical design were not conducive to longevity. For example, the  main
wiring harness between the mains transformer, the rear-mounted PSU  board,
the reservoir capacitors and the rear heatsink carrying the PSU  pass
transistors was executed in PVC-insulated cable which in service  became 
very
hot. Over the years this caused the plasticizer to leach out  and vigorously
attack any copper it could find. The result is extensive  radial cracking of
the insulation and corrosion of the wiring and  associated terminals. The
cure is to rewire the entire harness in modern  PTFE cabling, which is a
chore but not inordinately difficult and allows  easy replacement of the
reservoir capacitors at the same  time..................
-----------------
John
 
You hit the nail right on the head as to why I find it impossible to  share 
so many other folks' enthusiasm for this series of receivers.
 
With the 17xx series Racal seemed to be struggling with the crossover  
between hard wired valve receivers and them there new fangled PCB thingies,  and 
somewhere along the way they lost the plot.
 
I don't question the performance, but that central pod of fold out PCBs and 
 all the associated wiring was a big mistake.
Externally they were fine, very nice in fact, but from an internal  
ergonomics and quality point of view I believe they were a  disaster, whilst other 
UK manufacturers of the time, Marconi and  Redifon for example, were getting 
it right.
 
I must admit I wouldn't mind a 1778, but only because it seems to  be the 
best of the bunch and I've never played with that one.
However, I don't think I'd swap any of them now for my Redifon R1001, which 
 is just as good a receiver but with engineering design and all round  
build quality that is so much better.
 
regards
 
Nigel
GM8PZR