Fw: "SB"-Series AM Filter...PART 1

[Edward Swynar VE3CUI]

Greetings all!

Like many of you reading this, I'm sure, awhile ago I simply gave up any &
all aspirations of ever finding a reasonably-priced (a.k.a. "cheap"! Hi Hi)
SB-310-style 5-KHz wide AM filter for use in my '301...

Good fortune, however, led me to the electronic doorstep of Jan, N8LQR.
This fact---coupled with the  noble Amateur art of "...tinkering &
experimenting"---inspired me to MAKE MY OWN "cloned" homebrew version of
one of Heath's more rare i.f. filters.

The results, I am most pleased to say, have been wonderfully successful! In
side-by-side tests with two SB-301s---one with the "stock"
communications-quality 3.75-KHz filter, the other with my 5.0-KHz
clone---are obvious: fidelity is much improved with the clone...there is no
"muddiness" in the audio, and I am not inclined to off-set the tuning of
the receiver to improve the response of the highs.

Perhaps best of all, the filter is essentially HOMEBREWED! All you need is
an original "large size" stock Heath SSB filter (similar to those used in
the SB-300 & SB-400), and four crystals. I purchased my new "rocks" from
JAN CRYSTALS in Florida for about $60.00 TOTAL, including shipping---you
may shop around & do even better...

In any event, without further adieu, I am forwarding Jan's original
communications to me on this subject for beneft of all to read. If you'd
rather pay the sixty, or so, bucks & hope that eBay might turn up an
original '310 filter, then go ahead & delete these messages---however,  if
you take pride in rollin' your own,  read on, & invest that $60.00 into
something you & your own two hands can benefit from for years to come!

~73~ Eddy VE3CUI - VE3XZ



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From: n8lqr at juno.com
To: gswynar at MAIL.DURHAM.NET
Subject: Re: "SB"-Series AM Filter...
Date: January 5, 2000 4:02 PM

Hi Eddy:

You got every kind of  response to your question except the one you wanted!

The Heath AM crystal filter, Part no. 404-314 consists of the following
parts:

2 each part no. 404-306 crystals, 3393.7 kHz
2 each part no. 404-307 crystals, 3396.8 kHz
2 each part no. 28-3 phenolic capacitors,  0.56 pF
1 each part no. 20-130 dipped mica capacitor, 12 pF
1 each part no. 40-814 slug tuned, center-tapped coil, 115 uH
1 each part no. 85-157 printed circuit board

I will try to verbally describe the schematic diagram for you:

Starting at the upper left hand corner, the IN terminal,  draw a line
horizontally to the right to the first 3396.8 kHz crystal.  Draw a 0.56 pF
capacitor in parallel with it.  Continue on horizontally to a 3393.7 kHz
crystal.  The other lead of this crystal is the OUT terminal.

Back at the IN terminal, draw a line downward and then to the right to a
3393.7 kHz crystal.  Continue on to a 3396.8 kHz crystal.  Connect the
remaining lead of this crystal to the OUT terminal.  Draw a 0.56 pF
capacitor in parallel with the 3396.8 kHz crystal.