[Premium-Rx] Racal 1772/78

[machine.age]

Excellent and appreciated commentary.
Re silly money, these should be going for hundreds not thousands especially those with odd duck filters (the majority) in my experience

John England

Sent from my iPhone

On Aug 10, 2010, at 9:22 AM, Dan Rae <danrae at verizon.net> wrote:

> I have owned the same 1772 for nigh on 30 years now, for better or for 
> worse, but have so far refrained from adding to the exchanges, but I do 
> have some acquaintance with them, perhaps not to the extent of Pat McA 
> however :^) 
> 
> I suppose that getting this one was the start of the downward path that 
> led to my current excessive collection of Racals...
> 
> Before you all rush out and spend silly money on one, there are a couple 
> of negative points that nobody has so far referred to.  First the 
> variable BFO has a woeful lack of stability, of no import if you are 
> mainly using the radio for AM or SSB listening, but a real disadvantage 
> if you use CW or RTTY.  The crystal BFO option provided for on the board 
> will of course help and I have implemented this on both my 1772 and my 
> 1778, but the crystals are now very hard to source, my local 
> manufacturer has gone out of business.  
> 
> Secondly the system of IF filter switching used with diode switches is 
> less than perfect; possibly this was a design decision to give some 
> "context" around the wanted signal, but for some it is a disadvantage 
> since the best available filters like the 8 pole McCoys will have their 
> skirt selectivity degraded.
> 
> Also if buying, be aware that the majority of ex-RAF 1772s were fitted 
> with an odd arrangement of filters and filter switching with ISB and two 
> offset data filters. These can be modified back to the "standard" 
> arrangement if you can find the filters but is a real disadvantage in my 
> opinion.  The ex-RAF 1778s seem to have not been fitted with a wider 
> symmetrical  filter than 3 kHz which is a bit less than useful for AM 
> listening, but at least they have no offset filters.  I did have a large 
> number of the McCoy 6.8 kHz filters, but they have all gone now. 
> 
> Thanks to a generous list member my 1772 is now fitted with a first 
> mixer board with switchable roofing filters, the usual 12 kHz one and a 
> narrow 1.5 kHz one which switches in automatically with narrow IF 
> bandwidths.  This was built in 1978, several decades before Yaesu and Co 
> were doing it.
> 
> I suspect that the PCB manufacturing process was the best available at 
> the time.  There are no VIAs, small rivets were used to link top and 
> bottom, and the adhesion of the copper to the substrate is not that 
> good, but in all those I have seen it is fibreglass, not SRBP.  I think 
> it is a little unkind to blame the designers for any failings here, as 
> with the PVC wiring, how were they to know what forty years or more 
> would do? 
> 
> I still have a very yellowed clipping of the 1974 "Wireless World" 
> article by R.F.E.Winn, the head designer of the RA1772 describing the 
> concepts behind the design which still makes interesting reading.  I 
> have an electronic copy of this, if anyone would like it, it can be 
> emailed; requests direct please.
> 
> Dan
> 
> ac6ao / g3ncr
> 
> 
> 
> 
> 
> 
> 
> 
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