4Khz Filter Modification

The TS-870 has a 3KC stock filter (YK-88S2) located on the bottom side. By swaping out this filter for the Inrad 4KC filter (#475), you'll be able to have better sensitivity on receive with less "hiss". On the transmitt, you will gain better fidelity, the lows will be richer, tighter and more robust. The mids and highs seperation are also more noticeable. Furthermore, if you are using rack gear, you can push your EQ's and compressor harder without reaching the threshold of "tearings" as quickly. This is a very simple mod to do. The most difficult part is the removal of the stock filter out of the filter board.

A note on removing the filter board: You definitely want to make a simple sketch as to which jumper goes to where or simply take a digital picture of the thing before you start un-plugging.

So, to start, order from Inrad the so-called 2.1Khz filter kit (they have a link on their website regarding this), tell them that you only want the #475 filter (instead of the 2.1KC filter) for the 8.83 Mhz filter bank.
You won't need to change any filter on the 455 side. This kit comes complete with detail instruction on how to make the change, along with all the necessary parts and color illustrations.
No adjustment to the radio is needed for this modification. Below is a picture of how the 4KC Inrad filter is mounted in the radio with proper coax jumper.

Good luck and lets hear the mellifluous audio out the TS-870

Click HERE to see C131 Mod

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