"Gerry" <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- I haven't tried the R-4C mods in the Jan/Feb QEX for two main reasons. One is that the authors don't show any data to back up their claims for improved performance. Maybe they expect the reader to be impressed by their academic credentials listed at the end in order to quash criticism. After all, who would question the judgment of a BSc (Hons1), whatever that is? The other is that some of their assertions and interpretations of devices used are either incomplete or inaccurate. For example, their assumptions regarding the power supply are inaccurate and incomplete. They don't go into much detail and forge ahead with their own ideas. But who am I to question? The audio stage they used is indeed rated for 20 watts but that's in a 22 volt bipolar supply, plus AND minus 22 volts. In the 12V single supply they used it looks more like 2.5 watts, looking at the data sheet. And since the distortion and noise specifications apply only to bipolar supply and the data sheet doesn't show what happens in a single supply, noise and distortion can only be speculated. My experience has been that these two performance aspects increase, sometimes unpredictably when you deviate from the specified application data. I get questions from customers all the time regarding analog reference circuits published on the web with complete parts lists and data. They have a problem and swear up and down they followed directions only to find out they didn't use the referenced components and board layout. Of course, 2.5 watts is still pretty good, so maybe the LM1875 is worth trying, never mind the data sheet. The point is the LM383 (obsolete) aka TDA2002 and TDA2003 (updated TDA2002) should still be the preferred choice. My main point of contention about the authors in the article is they don't show anything to back up their claims. Some of them might be OK, like the SN602 product detector. Others like the so-called power supply and the AGC system: proceed at your own risk. My impression is the article shows a SYSTEM, not a series of improvements that can be incrementally applied. Frankly, I wonder how this article made its way into a respected technical publication like QEX.
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jim Shorney Sent: Sunday, January 22, 2006 7:48 PM To: DrakeList; Jim Pruitt Subject: Re: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C? "Jim Shorney" <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- On Sun, 22 Jan 2006 15:58:17 -0800, Jim Pruitt wrote: >According to the article itself (mods done on a late R4C with 6EJ7 first and >third mixer). Thanks, Jim. Sounds like mostly old stuff, re-done a little. I'm always wary of AGC mods, sice the AGC is so good to begin with and is what makes the R4C so "listenable". I did do the third mixer mod as descibed in Drakemods to my late R4C, and it seems to work as advertised. Otherwise, no other mods as of yet. >I did wonder about the LM1875 audio amp (20 watt). My R4C needs work >(motorboats) and I wanted to do the Sherwood PS4 mod and the audio amp. I >have a Velleman audio amp kit that I was going to use but in reading Bob >Sherwood (NC0B) mods a few decades ago in Ham Radio Magazine made me wonder >how my Velleman audio amp would work since Bob said to be careful about lead >lengths (had to be exact lengths or would oscillate). So the LM1875 audio >amp was the one mod I was considering but did not want to butcher my R4C. 20 watts sounds like massive overkill. I would worry about power supply loading with that monster, unless the gain is limited somehow. I've got one of the Velleman amps. It looks good and works as advertised on the test bench. I think the warnings are scare tactics to make sure that people follow the manufacturer's recommendations as far as component dress and circuit layout - the devices are not tolerant of sloppy construction, but they are stable and robust with a little care. The one change I did make was the capacitance in the feedback circuit to roll off the high end around 3 KHz; this is a hi-fi amp module, and response to 20 KHz in a communications receiver is NOT a good thing. I wouldn't be afraid of trying the Velleman amp, as long as you follow Bob's hookup recommendations. I just haven't gotten the round tuit that I need to put mine in my R4C yet. Thanks again for the info, Jim. I may have to look at the article and see what it says in more detail. 73 Jim -- Jim Shorney -->.<--Put complaints in this box jshorney (at) inebraska.com Ham Radio NU0C Lincoln, NE, USA EN10ps http://incolor.inetnebr.com/jshorney/ ---------------------------------------------------------------------- Submissions: [email protected] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ---------------------------------------------------------------------- ---------------------------------------------------------------------- Submissions: [email protected] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ----------------------------------------------------------------------
