[HBR] Re: Miller iron Core IF's Series 612 -- and crystal filters

[Byron Tatum]

Hello All-
    I am documenting measurements on the miller 612 and 512 series 455 khz. 
units { inductance, capacitance, coil spacing, etc.} Also, found answer to 
my question in QST article concerning Loran Blanker { 1963} where author had 
to disect a Miller 612, he describes construction, core size, etc.
----- Original Message ----- 
From: "Walt Hutchens" <waltah at earthlink.net>
To: "HBR Receiver List" <hbr at mailman.qth.net>
Sent: Wednesday, May 17, 2006 6:05 AM
Subject: Re: [HBR] Re: Miller iron Core IF's Series 612 -- and crystal 
filters


> Byron wrote:
>> I spent some time trying to learn the particulars of their construction,
>> such as the difference in coil spacing between the input IF {612-C1} and
>> output IF { 612-C4}. These are the iron core units which brings me to the
>> heart of my question : The IF coils are wound on a form that has a cap 
>> glued
>> on the end. So, I assume there are two iron powder cores secured inside 
>> the
>> form?
>
> This all sounds correct.  However, you can confirm it with one of
> those tiny (very strong) rare earth magnets which will be attracted
> to the coil form if there's an iron core of any kind in there.   Or a
> magnetic compass would also work -- the needle will swing if
> passed near the coil form.
>
> Kees posted:
>> QTY 22 NEW Crystal Filters. 1650 kHz center frequency. These are
>> brand new and in great shape. Simple connection with IN, OUT and
>> SHIELD. Labelled as NETCOM Center Frequency 1650 kHz MDL. 1435
>
> And certainly a bargain at $5 each.   However the bandwidth isn't
> stated.
>
> If you get one of these for an HBR project (and the bandwidth
> proves suited to your planned use) then one could build it as a
> single conversion receiver.   Just put the filter after the 1st mixer
> and use two 1650 kcs IF stages.  Ditch the second conversion and
> the 100/85 kcs IFTs and all that.
>
> I believe the reason the W6TC HBRs were developed as dual
> conversion receivers is that a decent crystal filter would have cost
> you at least a week's pay in 1960 and the extra conversion and
> lower frequency IFTs were cheaper.   Today, the situation is
> reversed if you can find a bargain filter that will work.
>
> (Using a crystal filter requires just a bit more care in layout and
> wiring if you're going to get high ultimate rejection, compared to a
> low IF with multiple transformers.)
>
> In fact, I'll bet you could do a decent filter using 1843 kcs
> microprocessor clock crystals at $1.20 each.   Mouser carries
> them both series and 13 mmf load parallel resonance: those might
> well be far enough apart to make a usable half lattice filter.  Or you
> might be able to use a bunch of either one in a ladder filter -- the
> issue with a ladder would be whether the coupling capacitor values
> would be reasonable with crystals at that frequency for 2-4 kcs of
> bandwidth. Would certainly work for a CW-only HBR, though.
>
> So many projects, so little time ... I'm still struggling with the
> chassis layout for the GC-HBR project.   The main discovery so far
> is that a 10" x 12" chassis isn't have a lot of room for 14 tubes.
>
> I did succeed in sawing off the back 1/3 of a three gang AM/three
> gang FM tuning cap to make a dual 370/dual 30 VFO tuning cap -- 
> the big sections tune the 1400 kcs VFO, the small sections will
> tune the 5.5 Mcs IF.   Three hours of "if you slip, it's trash."
>
> I am having trouble finding enough time to work on the project with
> all the usual work and the spring stuff, too.
>
> Walt
> KJ4KV
>
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