Yes there is a plate current position and it shows a definite rise in current with modulation. There are dual 5U4's in the supply feeding the finals and modulator and I swapped them both out with the same results. I am leaning towards Gary suggestion that there is an impedance mismatch causing excessive current draw. Does anyone have a 5100B or know what the impedance of the primary and secondary should be. I will try another set of caps this evening when I get home there are 2 , 40uf in series on the B+ line. ----- Original Message ----- From: "Gary Schafer" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" <amradio@mailman.qth.net> Sent: Wednesday, October 13, 2004 10:29 AM Subject: Re: [AMRadio] B&W 5100B Modulation Update
> Tom, > > Try a new rectifier tube if you have one and see what you get. > Easy way to check capacitors is to tack a new one in parallel with the > hv filter cap and see if you get any improvement. > > Does the 5100 have a meter position for modulator plate current? If so > what is it doing. > If you have the wrong impedance taps on the mod transformer, the > modulators may be drawing much more current than they should. Too high > an impedance tap into a low impedance final load will make the > modulators draw very heavy current. > > 73 > Gary K4FMX > > > Tom Elmore wrote: > > The caps are the first thing I should have checked and there is a good > > possibility they are dried up except I don't hear any hum in the audio when > > monitoring on the receiver. Also I can make at least 125 watts carrier and > > don't see much of a voltage drop on B+ when I run carrier only. > > > > -Tom > > ----- Original Message ----- > > From: "George Pritchard" <[EMAIL PROTECTED]> > > To: "'Discussion of AM Radio'" <amradio@mailman.qth.net> > > Sent: Wednesday, October 13, 2004 8:46 AM > > Subject: RE: [AMRadio] B&W 5100B Modulation Update > > > > > > Tom, > > It seems to me that the capacitor bank for the 600 volts is not working. > > Look at the B+ with a scope, and you may see the B+ drop at the audio rate. > > A "stiff" capacitor bank will show no audio waveform on the B+. If I'm > > right, the caps are died out. Is there any trace of Hum on the "dead > > carrier"? > > George AB2KC > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Tom Elmore > > Sent: Wednesday, October 13, 2004 12:35 PM > > To: amradio@mailman.qth.net > > Subject: [AMRadio] B&W 5100B Modulation Update > > > > > > Now that I have had some time to troubleshoot the B&W 5100B modulation here > > is what I found. The B+ is around 600 volts with no modulation and I as > > start to modulate and watch the scope when it reaches about 50% modulation > > the B+ drops from 600 to around 400 volts. I changed the final and > > modulator 6146 tubes and see the same results. The original modulation > > transformer has been replaced with a Chicago Standard Transformer > > Corporation # A-3891. When I remove B+ to the final's and terminate the > > modulation secondary into a resistive load of about 6k ohms I still see a > > significant drop in B+ as I start to bring modulation up. I don't have the > > original mod transformer and the manual I have doesn't say what the > > impedance should be. I have tried various other tap settings on the > > transformer secondary and don't see much of an improvement in reducing the > > amount of voltage drop. I wonder if it is possible that this mod transformer > > just will not work with this unit. Anyone have experience with mod > > transformers using 6146's as finals and modulators? > > > > Thank You > > Tom Elmore KA1NVZ > > Anchorage Alaska > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > > > ______________________________________________________________ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net >
