[Collins] T9

[Dr. Gerald N. Johnson]

An IF transformer in place of a single tuned circuit probably increases 
the IF gain while it improves the inherent selectivity and reduces the 
effects of signals leaking past the mechanical filters outside the pass 
band.

There was also the T4 mod applied to the later S-3B/C receivers which 
moved one of the AM IF transformers from the AM filter position to the 
plate of the second mixer to accomplish more of the same while giving 
even better protection keeping DC off the mechanical filters.

In S-3B/C receivers, these mods being factory made would indicate a 
later production which can't be told by serial number since the serial 
numbers were issued at random. Changes in emblem also hint at late 
productions, first the meatball in place of winged, then the Rockwell 
emblem.

There are service bulletins for these mods to the 3B/C, I didn't spot 
them immediately in my Collins data for the 75S-3 but they probably exist.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 5/22/2010 6:50 AM, Master Lee wrote:
> Hello All
>
> Every now and then I see a Collin 75S-3 receiver for sale and there is mention
> of the T9 transformer.
> What is so good about this option?
>
> 73 Lee
>
>