Modifications for the Kenwood TR-751

Modifications for the Kenwood TR-751
TR851E & TR751E with 9600

Hello, Carl!

I have read one of your messages - you have asked for modifications of TR851.

I am also using TR851E (European Version) and TR751E with my 9600 BD- Modem (G3RUH) with the following modifications:

When you remove the bottom panel, you can see immediately all you need to do the modifications:

        Varicap Diode D21

        IF-Filter CF1
        Discriminator IC2




View from bottom side:

 Power in                                        Antenna
----------------------------------------------------------------------
I                                                                    I
.                                                                    .
.                                                                    .
.                                                                    .
I                                                                    I
I           Quartz                                                   I
I           1       2                                                I
I            -D21-                                                   I
I                           I---I                                  ..I
I                           I...I CF1                                I
I                           I---I                                    I
I                                                                    I
I                                   1                                I
I                  ---------------------                             I
I                  I  IC 2  TA7761P    I                             I
I                  ---------------------                             I
I                  9                                                 I
I                                                                    I
----------------------------------------------------------------------
   Microphone                 Tuning Knob           Volume Contr.

IC 2 Discriminator
PIN 9 of IC 2 ------->- Capacitor (100nF) ------> -RX-Audio G3RUH-Modem

D21 Varicap-Diode
Pin 2 (has no ring!!) --------> TX-Audio G3RUH-Modem

IF-Filter (G3RUH recommands changing)
Replace CF1 ( 55 F ) with CFM 455 D

I thougt that the replacement of CF1 was too difficult for me. So I have asked a good friend to remove the PCB and to replace the filter...no problem, he said, and for him it was really not a problem.

The other modifications I have done by myself .
I have done the same modification to TR751 without changing the IF-Filter, because I only need TR 751 for uplink.

The components on the PC Board are close one to another, but I think that other TX/RX are more problematicly to modify.

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