The YK88S-2 was the stock filter on the TS-930 ... It had a bandwidth of 3.0khz which is nice for audio. It is no longer available for the 930 .....BUT the newer TS-870 use's the same filter and it is also labeled as the YK88S-2 ... I guess the bandwidth is the same ?? Check it out with someone that has the 870 service manual John