CW filter weirdness

[EP Swynar]

Hi Bob,

That website you referenced is probably THE one stop, go-to source for
anyone in search of filter info on the SB-series...

I am happy to state that, using the original info e-mailed to me by the
retired Heathkit engineer, I did, indeed, successfully construct the
extra-wide SB-310 "clone" AM filter several years ago, for benefit of my
SB-301. I used new crystals custom cut & purchased from JAN Crystals in Fort
Myers, Florida, and was quite surprised at how relatively easy the entire
project was to execute.

The cost for new crystals (then) was comparable to the then "going rate" for
pulled Heath AM filters on eBay --- but I had the added satisfaction of
having made the unit myself.

In retrospect, I should have perhaps experimented with the tuning of the
adjustable centre-tapped inductor before re-assembling the completed filter,
as the unit appears to exhibit a bit of a "dumble hump" when tuning across,
& peaking, AM stations...still, in all, this is VERY small hardship, in
light of how the filter really makes the SB-301 come alive & bright when
receiving AM...

Some final notes: I elected to use the larger-sized, older "SB-300" type SSB
filter in my SB-301 AM filter project...that choice necessitated my
installing the completed filter BENEATH the '301 chassis (it is affixed to
the chassis itself with a dab of silicone sealant, used as an adhesive).

I just thought the larger filter would be physically easier to work with...

Also, if you're contemplating high fidelity AM reception on your SB-300 /
301 receiver by simply replacing any & all IF filters with just a piece of
wire (or otherwise shorting-out whatever you have there), forget it: these
rigs do NOT use "conventional" IF transformers, as such --- the IF alignment
consists of peaking a simple, single L/C combo in each stage of
amplification. Period. In the absence of any crystal filter, the IF strip
simply runs "wide open" --- you'll hear dozens of stations all at the same
time, all across the tuning of the dial..."regular" coupled IF transformers
in  & of themselves afford some measure of selectivity, but this is most
assuredly not that type of receiver. All of the selectivity is achieved
through whatever crystal filter might be in use.

Good luck --- and do try building one of these filters for yourself. They
are NOT as difficult to execute, as they are intimidating...at first,
anyway!

~73~ Eddy VE3CUI - VE3XZ


***********************************


----- Original Message ----- 
From: "Bob Burns" <G3OOU at AOL.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Thursday, February 14, 2008 8:29 AM
Subject: Re: CW filter weirdness


> Hi All
>
> Information on the performance and content of Heath SB series crystal
> filters can be found at:
>
> _http://www.mines.uidaho.edu/~glowbugs/Heathkit%20SB_HW%20Filters.pdf_
> (http://www.mines.uidaho.edu/~glowbugs/Heathkit%20SB_HW%20Filters.pdf)
>
> 73
>
> Bob
>
> G3OOU
> G-QRP  6907
> _http://members.aol.com/rfcburns_ (http://members.aol.com/rfcburns)
>
>
>
>
>
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