Procedure to install 3rd filter for AM mode in Yaesu FT-101 E series
Parts required:

3 - small signal diodes  1N4148  (NTE  519)
2 - germanium diodes   1S1007   (NTE 109)
2 - 250uH RF choke coils
1 - .01 uF ceramic disk capacitor
1 - .047 uF ceramic disk capacitor
1 - 100 ohm ½ watt resistor  (actual 0.2 V drop across it in
use, indicates a much lower power rating will be more
than sufficient)
1 foot of light gauge stranded hookup wire
2 feet of shielded microphone cable
small perfboard ( 1" by 3" min.) with copper pads
small piece dbl. sided tape

and, of course, a Yaesu XF-30B filter, or equivalent
(unfortunately, these aren't cheap, and are currently
running $100+ on eBay.)
Of the Yaesu FT-101E type transceiver's few faults,
the lack of an AM mode filter is my pick for the
hardest to live with.  If you like to listen to SW or the
upper end of the AM broadcast band, the lack of the
filter makes the sound quality leave a little bit to be
desired. There's a modification to replace the CW
filter with an AM filter, but since I intend to use this
mode (eventually), this isn't an option.  I'd heard of
the elusive modification to add a third filter for AM,
but unable to find any 'how-to' information about it.
The only option was to work it out  myself.  Turns
out, it wasn't quite as hard as I expected. Hopefully,
I can explain the procedure simply enough, you can
do it yourself.  
Changes to the mode switch.

My transceiver had been previously modified and then unmodified.  
The wiring was a mess.  I decided to start from scratch, and will
assume your wiring is original, according to Fig. 1a and 1c. In any
case, verify your wiring to their connection points within the
transceiver.  Make notes and sketches.

Pull the power plug, remove the covers, move the speaker assembly
out of the way and remove the mode switch knob and nut/washer.  
Carefully pull switch from out of the panel and lift it up to where you
can get at it easily.

Identify and then detach the following three wires (Fig 1c) from the
mode switch (S2-c), and discard the diode.

1 yellow wire - runs to pin 9 on MJ3 (PB1183).  Grounding pin 9
enables the CW filter.  

1 red wire - runs to pin 7 on MJ-4 (PB1315, audio board)  

1 blue wire - runs to pin 12 on MJ3.  Grounding pin 12 enables the
SSB filter.

Fig. 1a shows the original and Fig. 1b the modified schematic of the
mode switch.
Take three signal diodes and solder to the mode
switch terminals as shown in Fig. 2.  I found it
helpful to twist the leads together and solder, then
cut and bend them into shape before soldering
them to the switch terminals.  I also found it
helpful to bend and double up the leads to form
small tabs to make it easier to solder the wires
onto the T and A terminals.

Solder the  piece of hookup wire to the AM
terminal, and route it down through the radio
towards the panel meter.  Then solder the yellow,
blue and red wires to the points shown in Fig. 2.

Carefully reinstall the mode switch, knob, and then
replace the speaker assembly.   This completes
the changes needed to be made to the mode
Changes to PB-1183 - IF board

Remove PB1183.  Take two pieces of shielded
microphone cable, and solder the center
conductor of one cable to one of the circuit traces
marked on Fig. 3, and the shield to a convenient
ground point.  Do the same with the other cable to
the other trace marked in Fig. 3.  Use caution to
avoid potential shorts from occurring between
cable and circuit board  traces.  Make a note to
identify cables as 'a' and 'b' to use when
connecting to circuit board in Fig. 4 later.  Use a
twist tie to secure cables to mounting screw hole
(not pictured) in upper left corner as viewed in Fig.
3, temporarily, to prevent strain on connections
during handling.  Reinstall PB1183.  Reuse the
twist tie to secure cables to mounting bracket and
replace mounting screws.
Filter wiring

The hardest part of this
project  is making a circuit
board to mount the filter.  I
used a small piece of Radio
Shack perfboard, 1inch by 3
inches and drilled to fit the
terminals on the filter.  I used
tinned wires soldered to the
copper pads as shown by the
dark lines.  They're looped
around the mounting posts on
the filter under the nuts, to
both ground the case and
provide for the filter ground
connections at the top .  It
would have been simpler just
to solder the components
directly to the wires. The 100
ohm resistor was soldered on
this side of the board.
That pretty much does it.  A piece of double sided
tape to mount the filter on metal box just behind the
VFO.  Take a minute to double check your work.  
Hopefully you'll have no issues.  Plug in power cord,
power on the transceiver.  Find a band with some
AM activity and note the exceptional increase in the
higher frequency audio. Check the other mode
positions for proper operation.   Power off, pull the
plug, and replace the covers.


Mike  kc8flu

If you have any questions, comments, suggestions,
email me.  
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