AVC BFO Switch

These notes are for at least three different versions of the radio. Select the appropriate sub-page below.

The AVC BFO switch its self appears to be the same part in all radios. There are two contacts on the back side of the wafer but since it is crimped to the switch frame, I was not able to photograph that side.

The letters on the terminals are used throughout these pages. F and C are not used.

Note the orientation of wafer in the pictures below is the same. The switch on the left is in the "BFO ON" or fully clockwise position.

From the schematic:

Notes on the AVG node:

• R1 is found in the RF 1 module on the bottom of T9. The wire from outside of the module goes to an otherwise unused terminal on the coil form. It took me an annoying amount of time to figure this out.
• In a similar manner, R7 is found in the RF 2 module on the bottom of T15.
• In the early radios, the wires to R1 and R7 come from a terminal on the unusual double row, eight-position terminal strip. In the later radios, they come from a normal three-position strip right next to the modules¹.

Early (left) and late (right)

For wiring, go to one of the following. SW8-14 doesn't play a role in this issue but it helps determine version.

Very early radio - does not have SW8-14 or SW8-15.

Early radio - has SW8-15, does not have SW8-14².

Late radio - Has SW8-15³.

Footnotes:

1. I only had three radios to check this on and none of them were SX-28A.
2. I don't think I have a schematic that has SW8-15 and does not have SW8-14. I do have two radios that fit that bill.
3. At this point, I'm assuming a late SX-28 and a SX-28A are the same at least as far as the BFO switch goes. There are differences in the general area.

Page: /AVC_BFO_switch/AVC_BFO_switch.shtml

Last modified: Wednesday, 10 Jun 2026