FT-102 Circuit Modifications
for
High Fidelity AM

by Bill - W3DUQ

 


AF Board
 Part Number Original Value New Value
 C02   .1 mfd  33 mfd
 C03  .001 mfd  remove
 C04  10 mfd  33 mfd
 C06  .0022 mfd  remove
 C07  1 mfd  33 mfd
 C08  1 mfd  33 mfd
 C09  10 mfd  33 mfd
 C10  4.7 mfd  33 mfd
 C17  4.7 mfd  33 mfd
 C19  33 mfd  100 mfd
 C20  4.7 mfd  33 mfd
 C21  4.7 mfd  33 mfd
 C76  .0027 mfd  remove
 C79  .01 mfd  remove
 C116  10 mfd  33 mfd
 C124  33 mfd  100 mfd

 

Note: If you desire to use the phone patch input for external audio feed, put 220k in series with the center conductor going to the patch input jack and a 1k to ground from the input audio side of the phone patch jack.

Also remove C04 (10mfd) from the AF unit to reduce the overall audio gain. I also changed R11 from 2.2k to 15k to set the gain properly for vox operation.

 

 

AM/FM Board
 Part Number Original Value New Value
 C12   10 mfd  33 mfd
 C70  .01 mfd  470 pf
 R03  4.7k Parallel with 180k to set carrier
level for extended positive peak modulation

 

Set both tone controls on the AF board to 50%. Frequency response is essentially flat from 40-6khz and down 3db at 16 khz. If you want it flat to 16 khz, just turn up the treble tone control a bit.

There is a problem with the alc kicking in too early on AM. To fix this, connect a 10k resistor between pins 2 and 3 of P22/J15 on the I-F board. This will raise the point at which the alc kicks in.

 

Back to the Modifications Page

 

  

17 December 2000