Hallicrafters WR-600 + NM0S CW Filter Kit

The 1968 Hallicrafters WR-600 (S-120) is nearly ready for use in CW QSOs after realizing Dave Cripe’s (NM0S) filter will provide the needed additional filtering. This video contains a sampling of Monday morning’s CW chatter on 40m. As the video shows, the filter has awesome performance; forget the fact this is a four-tube shortwave receiver built in 1968!
According to the filter assembly manual, it uses "four, two-pole Sallen-Key opamp filters; three low-pass filters, and one high pass filter. Each filter section is fairly low-Q, and the frequencies of resonance are staggered. Cascading these four sections in series creates the optimal filter response." The filter circuit is based on the Dave's May, 1994 article in '73' magazine. The filter kit is still listed for sale at less than $30 on 4sqrp website. The Four States QRP website has link to the magazine article, well worth reading.
The external Beat Frequency Oscillator (BFO) 455 KHz is a Ten-Tec kit module board kit model 1050, no longer in production. Antenna is half wavelength dipole inverted-V fed with homemade twisted-pair transmission line, and the feed point height is 26 feet (8 meters) above ground surface.
My next step is to use the Hallicrafters receiver in a CW QSO!
73 NG9D

[@w3tua]

I built the Hi-Per-Mite filter a few years ago and it is top notch! I'm using now with my old Kenwood TS-570D which has no filters. 73 DE WA5RR

[@AnthonyJones-vk6xq]

Glad to see a new video from you, 4SQRP offer some great kits, sadly for me they seem not to be available in Europe, would love to buy a CW audio filter for my old Tokyo Hy-Power HF-120 as an original cw filter is impossible to find these days ! Best 73 and thanks again for the upload.

[@paulinmt2185]

I have a S-120. Nice "modern" AC/DC SW set, but drift is a big issue on CW (as you illustrated), especially with the narrow filter. The filter really cleans up the audio. Good job riding the Bandspread. I still love my old Hallicrafters rigs. TNX ES VY 73 OC!

[@NG9D]

Hi Paul, Thanks for the comment. I just had an hour-long CW conversation with K5HZ and K9KEU on 80m using the Hallicrafters receiver and really didn't have much issue with drift. The old receiver does however make all received stations sound a little "classic"! Too much fun!! I will post a recording of that QSO to explain ... 73 Lynn

[@gcw2489]

Why do the received signals sound chirpy? Is that caused by the filter, the WR600, loading on the BFO, or a combination of all three? I don't recall that chirpiness on your other recordings. I didn't notice the chirp when you unplugged the filter and ran using the WR600 speaker.

[@NG9D]

Thanks, I noticed that too, and it seemed more pronounced on one station in particular. I’m going to have to listen to that recording again and try and figure out what’s going on. 73 NG9D