Don, I think the kiwa filters are the best thing since sliced bread! They use an op amp input, into three ceramic filters, picked to give the bandwidth you want, and an op amp output. It runs off 8 to 30 volts, and is about the size of a postage stamp. They come with shielded wires to hook up to the IF and power.
The shape factor seems quite similar to a good mechanical filter, very steep sides. In use, if someone is not wide (splatter), you can tune just off them and cant tell they are there at all. 5kc separation works fine with these filters. I have a 5.5Kc filter in the first homebrew, and got a filter board with switching diodes and two filters on it for the new homebrew. I picked 4.5 and 5.5Kc, 5.5 seems good fidelity, and works very well under most conditions, the 4.5 will be for when things get rough. Comparing the filter to the R390A filters, 4Kc is to narrow, 8 is to wide, but the 5.5 Kiwa filter is just right for me. People with ears that hear over 4kc might want wider filters. You can buy them in .5Kc increments, and they can come with 450 volt input and output caps for tube circuits. You just tack the filter on in the IF, after the mixer and before the first IF transformer. They cost $50.00, a web search on Kiwa will get their web site. They also make LCR meters, preamps, BC filters, and other stuff. A lot of their stuff is to improve various modern receivers. The filters may work so well, because they operate into just what they want to see, not loaded by the circuit, and they are very small and likely shielded well. I think 90% of the reason my receiver works so well is because of these filters. The filters will work in ANYTHING that uses a 455Khz IF frequency. Seems to work great, two high Q tuned circuits before the mixer, very good filter on the mixer output, really limits stuff you don't want from the receiver. I think these filters could really transform any older receivers that use a 455Khz IF frequency, and should try some in the Scott and the SX17, or even the R390A, get rid of 16Kc filter and put in a 5.5 or 6Kc Kiwa. You would then have 4, 5.5 (or 6), and 8 Kc, just the ticket for AM. In the 75S1, in place of the back to back IF cans, a Kiwa would be great, an add on low distortion AM detector, and you have a GREAT receiver in a small package. Even for something like a 75A4, the $50.00 Kiwa filters would cost much less then the mechanical filters, and they come in any bandwidth you want. I think you could solder the wires from the Kiwa filter onto pins you could plug into a mechanical filter socket... Plug and play! http://www.kiwa.com/ Brett N2DTS > > What kind of filter is the Kiwa (crystal, mechanical, > ceramic?), and do you > say they have no insertion loss? What is the skirt > selectivity like? What > bandwidths are available, and where can one purchase them? > > Don
