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I finally got around to
plugging this old Eddystone receiver into the mains supply to
see how it performs.. straight out of the box.. as it were.
The first thing I noticed was
the absence of a headphone jack socket (in my opinion a glaring
omission) and one must use the rear loudspeaker terminals. I
connected headphones to these and a signal generator to the aerial
terminals.
I then switched on the receiver
and noticed the dial lamps were pretty dim, but the receiver
warmed up and tuning it to Range 5 and 1MHz to match my generator
output gave a response at something like -84dBm (I noticed the
RF gain wasn't turned fully clockwise). I turned the gain to
maximum and connected a convenient 80m dipole and tuned across
the range. I found broadcasts at 560, 700, 890, 915, 982, 1033,
1060, 1097 and about 1115KHz but with a horrendous background
noise. Most noticeable was that all the recovered audio sounded
muffled and without clarity and also that the tuning response
didn't feel quite right. Switching on the BFO produced a very
weak response and twiddling the Crystal Phasing control indicated
this was working as was the selectivity switch. The Send switch
killed the radio as expected and AF and RF gain controls worked,
albeit a bit crackly due to disuse.
It'll need realignment.
Below
is the circuit diagram but click it to see it full size. |
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Now, a little more about the
receiver.
The design is that of a standard
single-conversion superhet with an IF of 450KHz and a frequency
coverage over five ranges of 480-1,120KHz; 1,100-2,500KHz; 2.5-5.7MHz;
5.3-12.5MHz and 12.3-30MHz.
The crystal filter parameters
can result in a shift of the IF by up to 1.5KHz and will have
a knock-on effect to the centre tuning position of the BFO. Its
possible that ageing of the crystal filter componnents might
increase the discrepancy in the final IF tuning which no doubt
can be compensated for in the settings of the various RF padding
components.
Thankfully, from what I observed,
bringing this receiver back to tip top performance shouldn't
be difficult. In fact the theoretical dial accuracy is quoted
to be better than contemporary standard test equipment so hopefully,
using a modern spectrum analyser and a Rohde & Schwarz signal
generator the end result may be better than when it left the
factory. |
