Are you sure you actually need to modify the ring mixer diodes?
When I got around to looking at one of my (now two) 525D's I noticed
there are a few differences even in the same model run. I've been
meaning to write these up for some time but for now here's one.
Over the life of the 525 (both analogue and digital) there seem to
have been (at least) three different RX mixer designs.
1. In the PDF scan of the original analogue Argosy there are two 1496
mixers on the board and no diode ring. The RX must have used a 1496
RX mixer at some point. I've not seen one of these but it is in the
scanned manual on the Unofficial TenTec pages.
<http://www.qsl.net/tentec/manuals/525.pdf>
2. Mentioned in KW7CD Ham Radio mods article for an analogue Argosy
that has a diode ring mixer with four discrete diodes (see the
description of the mod -- you replace the old diodes with the new
diodes on the board). I've not a picture or circuit diagram of this
design but I presume it's a minor modification between this one and
the next one.
3. In both of my 525D Argosy's I have the ND487C1 Quad Schottky Diode
ring "on a chip" so all 4 diodes are very well matched.
<http://www.qsl.net/tentec/manuals/525d.pdf>
People who have Argosy's could help by removing the top and looking
at the RF/Mixer board.
Does it have two 1496s U1 and U2 (two 14 pin dual in line ICs)?
or one 1496 U1 and a discrete set of diodes between the two small two-
hole toroids?
or one 1496 U1 and California Eastern/NEC ND487C1 a small round 4
legged "transistor-like" device between the two small two-hole toroids?
Not a great datasheet (there are better out there but I can't find it
again).
<http://www.datasheet4u.com/html/N/D/4/ND487_CaliforniaEastern.pdf.html>
The specs are very similar to the HP diodes for both forward and
reverse voltages and switching time. And of course they're all
matched by design :-)
Post the answer and the rigs serial number.
525 01611 ND487C1
525 02497 ND487C1
I also note that there are two different noise blankers for 525s.
<http://www.qsl.net/tentec/manuals/223.pdf>
The 223 and the 223A for Argosy's with serial number greater than 00824.
So I presume there was another design change in the RX at serial 824.
73
N7WIM
On Apr 19, 2007, at 6:46 AM, jmalloy wrote:
> Also: are the diodes mentioned in the KW7CD article still available?
> (They're spec'd as HP 5082-2800 and HP 5082-3081) If not, does anyone
> know of substitutes?
--
N7WIM / G8UDP
Kevin Purcell
kevinpurcell@pobox.com
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