[Hallicrafters] SX71 MOD, a reprise

Wed Mar 8 14:57:12 EST 2006

Phil (and all)

When someone takes the copyrighted work of another without permission, or 
does so with permission, you always credit the source and the author. To do 
otherwise is theft and/or plagerism, depending on whether or not the person 
taking said material 'claims' to be the author. What Gary Brown did was 
wrong and unethical.

Whether it is donated or whether it is not, what is on the HCI web site is 
copyrighted under that entity. If someone wants to reprintn something, they 
need to get permission from the Web Master first.

Gary is just complaining because once again he got caught being dishonest 
and is trying to pass the buck elsewhere.

The HCI policy is clearly stated. If you wish to reprint an item or photo, 
ask the Web Master first. Then credit the source and the author or 
contributor. What is there is for the benefit of all, but we also have an 
obligation to those who donate their work to protect it from theft, misuse 
etc. Not all of what is on the HCI web site is donated! Hence the "Get 
Permission First" policy.

Duane Fischer, W8DBF

----- Original Message ----- 
From: "Philip Atchley" <Beaconeer at sbcglobal.net>
To: "Magoo" <magoo at isp.ca>; <hallicrafters at mailman.qth.net>
Sent: Wednesday, March 08, 2006 10:14 AM
Subject: [Hallicrafters] SX71 MOD, a reprise

> Hi All,
>
> Sheesh, if I'd have realized what a firestorm all this was going to create 
> I would have kept my mouth shut, or rather, my fingers off the keyboard!
>
> Anything that I submit or come up with, whether on my web site or via 
> Email, is for the full benefit of the boatanchor community.  The SX71 
> "mod" (which I first posted in the form of an Email and which was 
> subsequently copied to the HCI site with my approval) that I came up with 
> was 'slightly' more than just the cathode resistor, I also changed the 
> screen bias etc. of the second stage.  Still, all pretty simple stuff. 
> All that the HCI folks did was copy my email to the Web-site and add some 
> advertising pictures to make it interesting.
>
> As far as I'm concerned, the written part that I produced can be printed 
> and may be freely used anywhere so long as there isn't any monetary 
> compensation (though if it's copied to any web-site etc. I'd appreciate 
> credit).  So far as I know, the PICTURES ARE HCI PROPERTY and any needed 
> permission should be definitely be obtained to use them.
>
> Since I originally wrote the article, and only parts of it made it's away 
> "around the circuit",  I'm re-posting a copy here from my own archives. 
> Enjoy!
>
> <Pasted in>
> I decided to take a '2nd' look at the SX-71.  While it played quite well I 
> never felt like it was doing all that a receiver with 3 IF stages should 
> do. Front end seemed sensitive enough, but overall gain and AGC action, 
> while a little better than 'most' receivers with 2 IF's like the 
> Hammarlund HQ-100, Halli SX-110 etc, just didn't seem to really have the 
> "punch".  After I overhauled Don's National NC183D that had 3 IF's and a 
> circuit design quite similar to the SX-71, that opinion was further 
> reinforced.  In that set I had to change a couple resistors (per factory 
> recommendation) to decrease the gain slightly as it was unstable.
>
> So anyway, I sat down with the schematic and tube manual to see if I could 
> determine why it's gain seemed so modest for the tube lineup.  Didn't take 
> me long to spot it.  The 2nd IF stage had it's tube cathode biased very 
> high and an unusually low screen Voltage on the screen grid.  So, I dug 
> out ye old trusty soldering iron and set the cathode resistor and screen 
> Voltage to the same level that the 1st and 3rd IF stages use, which is a 
> normal and expected value.  Voila! Gain and AGC action came up to my 
> expectations.  It won't affect overall sensitivity/noise figure as that is 
> mostly determined by the RF amplifier and first mixer stages.  What it 
> does affect, especially on the higher frequencies is how well the AGC 
> performs and how high you need to turn the volume on the weak stations. 
> Before you always had to 'crank it up' on weak stations on the 17 & 21MHz 
> bands, which is why I nearly always used the Ameco Nuvistor preamp over 15 
> MHz.  The thing really sounds good now and that is without the preamp!
>
> The SX-71 is claimed to be the first double conversion set on the market. 
> They also wanted the selectivity and perhaps a 'little' extra gain that an 
> extra IF amplifier gave them.  I can think of no explanation of why the 
> receiver was purposely 'tamed down' by crippling the 2nd IF and putting 
> coils that are sub par for the BCB band in an otherwise hot set.  Perhaps 
> 3 IF stages were so rare back then that they felt the "little" added boost 
> was sufficient, while now days we are used to all receivers having several 
> AGC controlled stages that give superb AGC action.
>
> <end of article>
>
> 73 de Phil,  KO6BB
> DX begins at the noise floor!
>
> THE BEACONEER'S LAIR:  http://www.geocities.com/ko6bb/
> MY RADIO-LOGS:   http://www.geocities.com/ko6bb/Logs/
> QSL GALLERY:       http://photobucket.com/albums/y123/KO6BB/
> Merced, Central California,    37.3N  120.48W  CM97sh
>
>
> ----- Original Message ----- 
>
>> Let's see if I have this sequence right-
>>
>> Someone discovers that changing a resistor in a stage leads to better 
>> performance and posts this for everyone's benefit.
>>
>> Someone else posts a message indicating that this mod is similar to one 
>> found in a pre-written article. That article is identified with a link 
>> for everyone to see.
>>
>> The author of this earlier article contacts the list administrator to 
>> protest that someone has hijacked his material without giving him credit.
>>
>> Right so far?  OK-so if I discover a mod for a radio and post it for 
>> everyone's benefit, not knowing that someone else has "discovered" this 
>> earlier and written an article on it then I am contravening "copyright" 
>> laws?
>>
>> Horse puckey!!  Let's get real!  I know Americans are a litiginous 
>> society but let's not get carried away here.  This is ham radio, not the 
>> great Blackberry steal.
>>
>> Bill, VE3NH
>
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>
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