Does anyone have an NESCAF, built or unbuilt? that they would part with? I'd really like to get one for the regen receiver I'm building. firstname.lastname@example.org
73, Jim K4AXF
If you can wait a few weeks, the revised NEScaf may be in stock here. Last rumblings I heard were hopeful about March.
73, Scott N1AIA
There is one on E-bay now.http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370330767909&ssPageNa...
Any update on when the next run of NEScaf might be?
Thanks for the inquiry. At this point, it looks like it may be a few more weeks. Dave, NT1U had redesigned the board to take a surface mount SCAF chip, but we have not done a proto run. Recently, one of our members pointed out another SCAF chip in the original dip-format from another manufacturer. This is supposed to be a drop-in replacxment for the original chip. I have some samples now.
I will be testing this possible replacement soon, and determine if we can just go with another run of the same board. The delay has primarily been due to lack of time on my part. I intend to get back to work on this after the MassCon gathering, this weekend.
As for me I'ld be for the replacable chip if it's as good or better than the original rather than the SMT Chip. Why fool with perfection!Very excitedly awaiting the release of the kit weather SMT or not.
I built a NEScaf last year and it seemed to be working fine. Trying it out again after several months of disuse it now makes a steady, tone at the filter center frequency even with no input. The tone pitch varies with the filter center and gets louder with the width control. With the bandwidth control fully counterclockwise the tone becomes painfully loud. With input applied I can hear the input signal faintly underneath the tone.
Any ideas on debugging?
I'm posting here because the web won't let me make a new topic.
KD8CGH Bob Benedict
Sorry for the delay in replying to you on this- Several of us have been very busy preparing for and attending the MassCon QRP convention this past weekend.
Also sorry to hear you are having trouble with your filter. I have not seen this particular failure mode. Your description sounds like perhaps the clock chip (555) is working properly, and since you DO have audio out, it also sounds like the amp chip is OK.
I think the problem most likely lies in or around the SCAF chip itself, or the wiring associated with it. If you used sockets for the ICs, I would try reseating the chips. Also check for poor solder joints- sometimes they can take a period of time to cause trouble. Another possibility is a broken wire lead to the bandwidth pot.
If you DID use IC sockets, you can remove the SCAF chip, and the tone should go away. You can then check the audio amp by touching the input pin with a screwdriver- you should be able to pick up some AC hum.
With an oscilloscope or freq counter, you could check the output of the 555 clock chip- you should see a signal at 10X the center frequency desired.
If all else fails, you can send the filter to me at my QRZ.com listed address, and I would be happy to look it over for you.
Still working on it . . .