As you will see in the new circuit there is an audio filter to be
made consisting of a LF choke and a couple of capacitors (a Pi
network in fact) It asks for a 1 henry choke which I didn’t have
so I used the primary of an old transistor radio output trans-
former as the choke and adjusted the capacitor to give me a
cut-off at about 3 kHz using an audio generator and an oscillo-
scope.
Once you are happy with the filter put it on one side.
See Figs.13. 14 & 15
Next we have to re-route the existing audio via the BFO on/off switch so moving to the opposite corner of
the set we have V7 and V13 next to each other. Looking at pin 2 of V13 follow the wire (green in my case)
up to the junction of two 100k resistors which are R 41/42. Remove this wire.
Now using either a screened twisted pair cable (I used a bit of Type 1 audio screened cable ) or alterna-
tively a couple of thin screened coax’s, connect pin 2 of V13 to the centre of the empty side of the BFO
switch and the junction of the two 100k resistors to the top contact of the BFO switch (so reinstating the
existing audio routing.)
Whilst we are down in this area it would be prudent to solder the extra 22pf capacitor across the 8pf ca-
pacitor that is at the end of the coax leading to the ex BFO can. NB: 22pf may be to big and give detector
overloading but use this to start with or alternatively a 30 pf trimmer for better adjustment after finish).
See Fig.16 below
Having completed the connections around V7 we now move
to the reinstallation of the now ssb can (ex BFO can)
Replace the two side screws at the top side of the can and slip
the can through the chassis and inspect the new anode feed
isn't touching the chassis. If it is then bend and insulate.
Once happy, replace the two holding screws at the bottom
through the chassis.
Next reconnect the BFO variable capacitor. We now have to extend the feed from the EX BFO switch to
the HT connection on the SSB can using the 3.3k 2 watt resistor and smoothing capacitor ( 10uF is recom-
mended however I used what I had which was an 8uf and it didn't make any difference).
Fig.12.
Fig.13.
Fig.14.
Fig.15.
Fig.16.
