[TenTec] OMNI D 546 Series A mods?

[W9CW@aol.com]

I am sure I am repeating this, but here is a quick synopsis of the original 
Omni models:

Omni A (analog display) Series A
Omni D (digital display) Series A

The Series A only had the 2.4kHz SSB xtal filter with active audio CW 
filters.  And, it had the Squelch (this easily determines it's the Series A). 
 

Omni A Series B
Omni D Series B

The addition of a PIN diode switched daugher board above the standard 2.4kHz 
filter for a 1.8kHz and 500kHz filter.  Additionally, the Squelch control was 
replaced by an audio notch filter.  The xtal filter switching, and the 
respective audio filters, were selected by a rotary switch.

Omni C (only available with digital readout)

Independent toggle switch selection of xtal and audio filters.

Obviously, there are other differences as well, including optional or 
built-in WARC freq coverage, RIT/XIT, Fast/Slow QSK selection, etc., but the 
above delineates the major differences.  Board updates and changes also 
occured through the Series changes as well.

I've owned all three types, and currently use the Omni A Series B as my main 
CW rig, in conjunction with cascaded Datong FL-1 and JPS NIR-12 audio 
filters.  This may not be state-of-the-art, but I can work anything I hear.  
I use a 500Hz CW xtal filter in the 1.8kHz slot, and a 250Hz in the 500Hz 
slot with I.F. gain mods to compensate for the insertion loss of the filters. 
 As it is used only for CW, the analog freq readout is perfectly fine for me.

73,
Don W9CW