Restoring a RACAL RA-237B Low Frequency Converter – Gerry O’Hara
I purchased and restored a RACAL
RA-117 a couple of years ago.
This radio has been working very
well since the restoration, but I
found that it only received signals
down to around 750kHz, below
which I receive mainly spurii and
noise – not too surprising, as the
receiver is only designed to receive
down to 1MHz at full spec and
below this with ‘reduced
performance’. I knew that a low
frequency (LF) converter was
available for this receiver,
designated the ‘RA-237B’ and
decided to look-out for one of
these to mate with my receiver.
Finding an RA-237B
I had been keeping
an eye on Ebay
and other potential
sources for one of
these (fairly
scarce) units over
the past couple of
years and finally
found one for sale
on Ebay - ‘locally’
here in British
Columbia (actually
in the Okanagan),
which meant I would still be incurring some shipping cost (but not much). I won the auction and
secured the unit for a reasonable cost. On arrival, the unit was well-packed and in pretty good
shape, with a full tube complement and, thankfully, a copy of the RA-237B manual (which is not
readily available for free download on the web).
The RA-237 v the RA-137 v the RA-37 and the ‘B’
The RA-237 unit is a modification of the RA-137 unit which is
designed for the RA-17 receiver, the primary difference
between the two models is the addition of a 2MHz crystal notch filter to help remove remnants
of any 2MHz local oscillator signal due to any imbalance in the balanced mixer in the RA-237,
