"SB" Series AM Filter...PART 2

[Edward Swynar VE3CUI]

 Hi gang...

 Here's part 2 of Jan's communications to me re. the Heathkit line of i.f.
 filters, as were/are employed in the "SB" series of
 receivers/transmitters/transceivers...

 BTW, the "large" size filters all used standard HC-6/U crystals in
 them---the "small" size filters have the "flattened" HC-6/U type crystal
 (same height, cross-width, pin spacing, etc., only not as thick). So as
not
 to bother with drilling/modifying my receiver, my HB filter was attached
to
 the underside of the  SB-301 chassis with a dab of silicone sealant ("RTV"
 sealant); additionally, I employed shelded wire to make the connections to
 the switch wafers.

 ~73~ Eddy VE3CUI - VE3XZ
 -------

Fom: n8lqr at juno.com
To: gswynar at durham.net
Subject: Re: "SB"-Series AM Filter...
Date: January 9, 2000 10:27 PM

Hi Eddy:

Hope you don't mind the delayed response to your e-mail.  I download my
e-mail only every 4 or 5 days.  I use Juno,  which is free,  on a 12 year
old Zenith Data Systems computer.  This way, if I get any viruses I don't
mess up our family computer!

I'll try to answer your questions:

1) What's the difference (if any) *electrically* between the original
larger SB-300 SSB filter & the physically smaller SB-102 sized unit?

The two filters have the same input and output impedance--2 kohms, the
insertion loss is also the same--4 dB.  The bandpass shape factor is
slightly better on all of the smaller filters than on the larger ones. The
insides of the two filters are different.  Electrically the two filters are
interchangeable.  Mechanically you have to drill new mounting holes to
interchange the filters.

 3) Are the *internal* parts that much smaller physically, too? (can I use
standard-size HC-6U crystals inside of an SB-102 style case?).

The first part of this question I don't know.  I don't have the blueprints
for any of the large filters and I have never taken any of them apart.
They were designed before my time at Heath Company.  I started working
there in the spring of 1967 when the SB-301, -401 were coming out.  The
answer to the second part of your question is "yes".

In fact the HC-6/U crystals are what  Heath used in the smaller cases.

 3) What was the size of the 404-314 filter, anyway---SB-300 size, or/
SB-102
size...?

The 404-314 AM filter is in the smaller case size--like the 404-283 SSB
filter.

4) How did Heath arrive at the value of those "0.56-pfd." capacitors? Were
they the result of "trial & error"...? If so, would I have to experiment
with the value of these two capacitors in order that my own choice of
crystals might play properly...?

Yes, the final  values  were arrived at by cut-and-try  for the best
bandpass response.  However all 404-314 filters use the same value
capacitors. In other words, the capacitors are not tweaked for each filter
individually. I think you will have to do the same with your home built
filter because your crystals will most likely have different capacitances
than Heath's. The slug tuned coil adjusts the center frequency of the
bandpass.

I hope to build one of these up from your description into my SB-301
receiver (with the physically smaller filters)---if the design is such that
I have to incorporate the larger outer casing, I have no problem with
drilling extra holes on the '301 chassis to accommodate same.

All four HC-6/U crystals and all associated parts will fit inside the small
case size, so you won't have to drill any new holes in the chassis of your
SB-301.  In fact, don't even mess with the larger case size filters. They
were used only in the  SB-100, -300, and -400.

Here is a list of the large size filters that Heath used:

Part no.     Type     Bandpass, 6 dB--60dB     Used on
404-200     SSB     2.1 kHz     5 kHz              SB-100, 300, 400
404-201     AM        3.5 kHz     14 kHz                 "        "      "

404-202     CW      400 Hz      2.5 kHz                 "         "

Here is a list of the small size filters that Heath used:

Part no.      Model no.    Type     Bandpass, 6 dB--60 dB   Used on
404-283     SBA-310-2  SSB     2.1 kHz    5 kHz            SB-301, 310,
401, 101
404-284-1 SBA-301-2  CW       400 Hz     2 kHz                  "        "
404-285-1 SBA-301-1  AM        3.75 kHz  10 kHz                 "       "
404-314         --------       AM        5 kHz       15 kHz at 50 dB SB-310,
-313 only
404-328     SBA-310-1  SSB     2.1 kHz     7 kHz                SB310,
HW100, 101
404-548         --------       CW       400 Hz     2 kHz        SB-104,
-104A only

Be careful if you ever get a 404-548 CW filter!  It will only work in the
SB-04, -104A  because its center frequency is different than the other CW
filters!

Notice that there are two AM filters:  The 404-285-1 is the "DeLuxe" AM
filter. It was used in the ham rigs.  The 404-314 is the filter that was
used only in the SWL receivers.

I hope I haven't made any mistakes in the above lists.  If you have any
other questions, e-mail me and I will try to help.

Why do you want an AM filter in your SB-301?  Do you use it with any AM
transmitter?  If so, which one?

Jan Maldups, N8LQR
Kalamazoo, Mich.

Sponsored by the City of Tempe 

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