Jim, You may have just provided me an answer to an issue I have with a BC779 !
de KA4JVY Mark --- Jim candela <[EMAIL PROTECTED]> wrote: > > Rick, > > I understand your feel for the nostalgia, and passion for pursuing it. > All of us more or less on this group have some common ground here. > > I'd like to relate a story however to make a point. I have an RCA AR-88 > receiver. This 'heavy' boat anchor has multiple chokes, and oil capacitors > in the 250 volt power supply. I don't recall the values, or whether the > first choke was swinging or not, but I do recall the problem. I started a > project to beef up the audio from the receiver. This included extending the > LF response to 50 HZ, and multiple negative feedback paths around the audio > output tube (6K6?). What happened really surprised me. The power available > below 300 hz steadily dropped off, but much steeper than I anticipated. It > turned out that I had over 50 volts P-P ripple on the B+ whenever I cranked > the audio up when listening to AM broadcast 'male' voices. I looked at the > B+ on a scope, and I'll never forget what I saw. The waveform was going up, > and down with the audio, and sometimes exploding in amplitude when a certain > audio pitch was being sent to my loudspeaker. It was kind of like a > automobile driving over speed bumps, and not having any shock absorbers! > > The problem was filter resonance excited by the audio rate draw by the audio > output tube. In the end, a single 100 uf 450V capacitor across the B+ cured > the problem, and I had nice clean bass down to 50 hz as desired. > > As far as resonating a smoothing choke, this is not new stuff, so you might > keep that option on the table. At the following link I have an example of > where I did this with good success. The supply was already choke input, but > the critical inductance was not met, so the regulation was poor, and the > ripple was higher than I wanted. By simply resonating the choke, both > problems were solved. Here is the link: > > http://pages.prodigy.net/jcandela/CE20AQRO/PS.JPG > > Regards, > Jim > JKO > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Rick Brashear > Sent: Thursday, May 04, 2006 9:58 AM > To: Discussion of AM Radio > Subject: Re: [AMRadio] Smoothing Choke > > > Jim, > I appreciate your take on the power supply and agree for the most > part. Even though this particular ART-13 will see little if any CW > operation I would like the supply to be as stable and clean as > reasonably possible. You are absolutely correct about the difference of > availability of capacitors and chokes in today's world versus the days > of W.W.II. I considered using more modern components and at one time > even thought about an all solid state power supply. It would be much > easier and cheaper to construct and less expensive to operate with less > heat. However, the lure of the olden days kept calling me back to > glowing tubes and swinging chokes. So, even though I agree that with > modern technology applied I could have a cleaner, lighter and less > expensive supply, I will likely stay with the old school thinking on > this one. That is IF I can get the ripple to a low enough level so as > not to cause problems on the transmitted signal. > Thanks again for your advice and explanation, you make a very valid > point and one which would serve my project well. > 73, > Rick/K5IZ > > > > Jim candela wrote: > > >Rick, > > > > Sorry but I am going to throw a wrench into this discussion. Those > >swinging choke power supplies, although useful, have been out of favor for > >years... > > > > > > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.385 / Virus Database: 268.5.2/329 - Release Date: 5/2/2006 > > -- > No virus found in this outgoing message. > Checked by AVG Free Edition. > Version: 7.1.385 / Virus Database: 268.5.2/329 - Release Date: 5/2/2006 > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
