[Premium-Rx] Plessey PRS 2280 series

[Michael O'Beirne]

Good afternoon group,

Regarding the continuing PRS 2280 thread, my ex-Plessey contact comments as 
follows:-
>
> "Your understanding of the 2280 family numbering is entirely correct.  In
> view of the limited production run anticipated for each variant, only one
> silk screen was commissioned for civvy use."
>
>>Q. Someone referred to the 2282A with a digital BFO presentation.
>
> "I can't recall anything much of this model.  Quite a few variants were
> made
> for the RAF, the Swedish military, GCHQ and other people.  Some of them
> had
> front panels of different colours and/or different languages."

He adds that only a few were sold to GCHQ partly because they were concerned 
about the overheating problems of the PSU of the earlier PR2250 (from which 
the 2280 was derived).

In fact as regards the 2250, I share Paul Reeves' comments made today that
arguably the 2250 is a better set.  My same Plessey contact agrees, as do
several other professionals.   I am not at all surprised to hear that the
Royal Navy still use them.  I had heard a while back that quite a few were
in use at the RN/USN intercept station just south of Scarborough - (Staxton
Wold?).   However, the 2250's unusual construction makes it a bit of a pain
to work on, as I am discovering to my cost.   I thought it was the PSU
module (usually the Achilles' heel) but mine seems OK under external load
and I think that some other faulty module is pulling down one or more of the
supply rails.

When the 2250 was working it delivered a most acceptable audio quality.  A
couple of drops of thin machine oil into the shaft bearing improved the
tuning feel.

You can do even better by replacing the tuning knob with a heavier one.  I
use a spare for an RA17.  If you look underneath one you will see that the
knob is mostly hollow and, most importantly, it is completely symmetrical
because the fixing mechanism is a centre screw clamp, as you get on many
Sifam knobs, not a grub screw in the side.  I filled my knob level to the
top with outdoor quality "Polyfilla" compound, the stuff we use in the UK to
fill in holes in walls prior to redecoration.  This gritty grey/pink stuff 
is better than the finer white internal Polyfilla. It trebles the weight of 
the
knob.  I can now flick and spin the knob like a traditional Eddystone
receiver - no, better, as there is almost no mechanical drag!

I have another RA17 knob filled to the top with molten lead, and that is 
really heavy, but before you all rush off to visit your local church roof, 
take note that the whoever filled my one did not get the weight completely 
evenly distributed.  I guess you don't argue much with molten lead as you 
pour it!!   The result is that there is a small imbalance that causes the 
knob to turn to one position.  I suspect one could remove this by carefully 
filing the lead or adding small drops of Araldite, like balancing a car 
wheel, but that's a lot of fiddly work.  There is no such problem with 
Polyfilla and smoothing off evenly with a flat knife.

73s
Michael
G8MOB